Android multiple buttons alignment

Android multiple buttons alignment - android

I'm testing Android Studio and I'm trying to write a simple calculator just to test it andl learn Android.
What I'd like to achieve is something like this:
and I'd like to have this behavior with every device, either portrait or landscape.
What I've though is to make everything relative to the string "Result is 0:", so something like this:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="org.mennini.mycalc.MainActivity$PlaceholderFragment">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Sum is: 0"
android:id="#+id/textView"
android:onClick="onButtonClick"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="8"
android:id="#+id/button"
android:layout_marginTop="40dp"
android:layout_below="#+id/textView"
android:layout_centerHorizontal="true"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="7"
android:id="#+id/button2"
android:layout_alignTop="#+id/button"
android:layout_toLeftOf="#+id/button"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="9"
android:id="#+id/button3"
android:layout_alignTop="#+id/button"
android:layout_toRightOf="#+id/button"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="5"
android:id="#+id/button4"
android:layout_below="#+id/button"
android:layout_toRightOf="#+id/button2"
android:layout_marginTop="19dp"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="4"
android:id="#+id/button5"
android:layout_alignTop="#+id/button4"
android:layout_toLeftOf="#+id/button4"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="6"
android:id="#+id/button6"
android:layout_alignTop="#+id/button4"
android:layout_toRightOf="#+id/button4"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="2"
android:id="#+id/button7"
android:layout_below="#+id/button4"
android:layout_toRightOf="#+id/button5"
android:layout_marginTop="19dp"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="1"
android:id="#+id/button8"
android:layout_alignTop="#+id/button7"
android:layout_toLeftOf="#+id/button7"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="3"
android:id="#+id/button9"
android:layout_alignTop="#+id/button7"
android:layout_toRightOf="#+id/button7"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:id="#+id/button10"
android:layout_below="#+id/button7"
android:layout_alignLeft="#+id/button8"
android:layout_alignStart="#+id/button8"
android:layout_marginTop="19dp"
android:layout_toLeftOf="#+id/button9"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="."
android:id="#+id/button11"
android:layout_alignTop="#+id/button10"
android:layout_toRightOf="#+id/button10"
android:onClick="onButtonClick" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="C"
android:id="#+id/button12"
android:layout_below="#+id/button10"
android:layout_centerHorizontal="true"
android:layout_marginTop="30dp"
android:onClick="onButtonClick" />
With an off number of columns is easy, but how can I deal with an even number, such in the example?
More, with Android Studio I've tried to use Table Layout and Grid Layout, but I haven't understood how to set a grid with specific number of rows and cols, i.e. a 5 rows x 4 columns grid, i.e. I can drag a GridLayout and set the number of rows and columns, but as I drag over it some controls, say a Button, I see underneath a green grid with a lot more cells than expected, so my intention to draw button on my 5x4 grid and have the grid itself horizontally centered gets frustrated.
Finally (thanks for reading up to here) the question: how can I deal with this situation? Is my idea of using all buttons relative to textview good or stupid?
Is my idea of using a GridLayout a good or stupid idea?
In which smart way can I deal with this problem????
Thanks a lot

you can use linearLayout and give needed weight.
here is my code which I gave 1/5=0.2 weight for each row and 1/4=0.25 for each column.
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
>
<TextView
android:id="#+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:onClick="onButtonClick"
android:text="Sum is: 0"
android:textAppearance="?android:attr/textAppearanceLarge"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="300dp"
android:layout_marginTop="32dp"
android:orientation="horizontal"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView">
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.5"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:orientation="horizontal">
<Button
android:id="#+id/button14"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="+" />
<Button
android:id="#+id/button15"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="-" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:orientation="horizontal">
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="7" />
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="8" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:orientation="horizontal">
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="4" />
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="5" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:orientation="horizontal">
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="1" />
<Button
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:text="2" />
</LinearLayout>
<Button
android:id="#+id/button17"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="0" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:orientation="vertical">
<Button
android:id="#+id/button6"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="*" />
<Button
android:id="#+id/button7"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="9" />
<Button
android:id="#+id/button8"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="6" />
<Button
android:id="#+id/button9"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="3" />
<Button
android:id="#+id/button10"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="." />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:orientation="vertical">
<Button
android:id="#+id/button4"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.2"
android:text="/" />
<Button
android:id="#+id/button5"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.8"
android:text="Enter"
android:textSize="12sp"/>
</LinearLayout>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

Have you ever thought about using TableLayout?

you can thought about Linear Layout with vertical orientation for first three columns (each row added to individual linear layout with Horizontal orientation, which means that you need for four linear layouts, then all added to first layout which Linear Layout with vertical orientation), then add the first Linear layout and the last column (which added first to another vertical layout) to another linear layout with Horizontal orientation!
Here also you can find good example:
http://mrbool.com/how-to-create-a-calculator-app-for-android/28100
Also here full xml code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/plus"
android:text="+"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/min"
android:text="-"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/mul"
android:text="*"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/seven"
android:text="7"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/eight"
android:text="8"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/nine"
android:text="9"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/four"
android:text="4"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/five"
android:text="5"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/six"
android:text="6"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/one"
android:text="1"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/two"
android:text="2"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/three"
android:text="3"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/one"
android:text="1"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/two"
android:text="2"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/three"
android:text="3"
/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/zero"
android:layout_weight="2"
android:text="0"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/dot"
android:text="."
/>
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/slash"
android:text="/"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "#+id/enter"
android:layout_weight="2"
android:text="Enter"
/>
</LinearLayout>
</LinearLayout>
regards #Sandman42,

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:paddingBottom="#dimen/activity_vertical_margin" android:paddingLeft="#dimen/activity_horizontal_margin" android:paddingRight="#dimen/activity_horizontal_margin" android:paddingTop="#dimen/activity_vertical_margin" tools:context=".Home" android:background="#fff" > <EditText android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="#string/disp" android:id = "#+id/display" android:hint="#string/dispHint" /> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="center" android:gravity="center" android:paddingTop="20dp"> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/seven" android:text="#string/seven" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/eight" android:text="#string/eight" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/nine" android:text="#string/nine" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/div" android:text="#string/div" /> </LinearLayout> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="center" android:gravity="center" android:paddingTop="20dp"> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/four" android:text="#string/four" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/five" android:text="#string/five" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/six" android:text="#string/six" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/mul" android:text="#string/mul" /> </LinearLayout> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="center" android:gravity="center" android:paddingTop="20dp"> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/one" android:text="#string/one" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/two" android:text="#string/two" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/three" android:text="#string/three" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/sub" android:text="#string/sub" /> </LinearLayout> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="center" android:gravity="center" android:paddingTop="20dp"> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/cancel" android:text="#string/cancel" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/zero" android:text="#string/zero" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/equal" android:text="#string/equal" /> <Button android:layout_width="55dp" android:layout_height="wrap_content" android:id = "#+id/add" android:text="#string/add" /> </LinearLayout> </LinearLayout>

Related

How to make a numpad similar layout in android

How do i make the numpad layout as shown in the uploaded picture.
This is my current code which would not show anything in the design view. I used this code previously on other views which work but this time it does not work and none of the buttons were visible at all in the design view.And also how do i make the 0 button as it is in the picture. This is my 2nd time asking questions in stackoverflow so do let me know if my questions are not clear and also english is not my first language. Thank you in advanced!
Edit: I have to make this layout through xml coding and not the usual thing
where the users click on the textview and the numpad of the phone
shows up. I hope this clarify the doubts of my question. I have to
make the clear, cancel and exit button as well.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:weightSum="4"
android:layout_weight="4"
android:background="#drawable/background"
tools:context=".insert_amount">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="250dp">
<VideoView
android:id="#+id/videoview1"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</LinearLayout>
<TextView
android:id="#+id/textview1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Player"
android:textSize="30dp"
android:layout_marginTop="10dp"
android:layout_gravity="center_horizontal"
android:textColor="#color/white"
/>
<TextView
android:id="#+id/textview2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Display ID"
android:textSize="30dp"
android:textStyle="bold"
android:layout_marginTop="20dp"
android:layout_gravity="center_horizontal"
/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#drawable/content_box"
android:layout_marginTop="10dp"
android:layout_marginStart="50dp"
android:layout_marginEnd="50dp"
android:orientation="vertical">
<ImageView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:src="#drawable/in"
android:layout_gravity="center_horizontal"
android:layout_marginTop="50dp"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Top Up Amount (IN)"
android:textSize="30dp"
android:layout_marginTop="10dp"
android:gravity="center_horizontal"
/>
<TextView
android:id="#+id/textviewnumber"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:hint="0.00"
android:textSize="40dp"
android:textStyle="bold"
android:gravity="center"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:weightSum="4"
android:orientation="horizontal">
<Button
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_weight="1"
android:background="#drawable/login_signoutbutton"
android:layout_height="fill_parent"
android:text="1"
/>
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="fill_parent"
android:background="#drawable/login_signoutbutton"
android:text="2"
/>'
<Button
android:id="#+id/button3"
android:layout_width="0dp"
android:layout_weight="1"
android:background="#drawable/login_signoutbutton"
android:layout_height="fill_parent"
android:text="3"
/>
<ImageButton
android:id="#+id/buttonclear"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="fill_parent"
android:paddingLeft="20dp"
android:paddingRight="20dp"
android:scaleType="fitCenter"
android:background="#drawable/login_signoutbutton"
android:src="#drawable/clear_button"
android:layout_margin="20dp"
/>

Try this
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="#style/ThemeOverlay.AppCompat.Light">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="Player"
android:textColor="#FFFFFF" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="12345679"
android:textColor="#FFFFFF" />
</LinearLayout>
</android.support.v7.widget.Toolbar>
<ImageView
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:src="#drawable/kid_goku" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="10dp"
android:text="Top up Amount" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:hint="Top up Amount" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="20dp"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:orientation="horizontal">
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="1" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="4" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="7" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="2" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="5" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="8" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="0" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="3" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="6" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="2dp"
android:layout_marginHorizontal="2dp"
android:layout_weight="1"
android:text="9" />
</LinearLayout>
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.5"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="40dp"
android:layout_marginHorizontal="2dp"
android:layout_marginTop="8dp"
android:layout_weight="1"
android:background="#9b5006"
android:drawableLeft="#drawable/ic_camera"
android:text="Clear"
android:textColor="#FFFFFF"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="35dp"
android:layout_marginHorizontal="2dp"
android:layout_marginTop="15dp"
android:layout_weight="1"
android:background="#9b5006"
android:drawableLeft="#drawable/ic_camera"
android:text="Cancel"
android:textColor="#FFFFFF"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="35dp"
android:layout_marginHorizontal="2dp"
android:layout_marginTop="12dp"
android:layout_weight="1"
android:background="#9b5006"
android:drawableLeft="#drawable/ic_camera"
android:text="Next"
android:textColor="#FFFFFF" />
</LinearLayout>
</LinearLayout>
</LinearLayout>
</LinearLayout>
OUTPUT

Your layout height exceeding the device display. You have to use ScrollView here. Also for making the number keypad using GridLayout link will be better choice and you can easily get '0' button position using this view.

Android: Place 4 buttons on RelativeLayout

I am trying to place 4 buttons to fill all the relative layout.. I want each button have width and height till the center of the RelativeLayout (with about 2dp space between them).. I don't think that I can explain it very good, so I have made an image and here is the code I have made... Any ideas?? Thank you!! The view right now is:
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="TextView"
android:textAlignment="center"
android:textSize="30sp"
android:layout_marginTop="10dp"
android:id="#+id/textView" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="#+id/textView"
android:layout_centerHorizontal="true"
android:layout_marginTop="35dp"
android:layout_marginBottom="10dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:id="#+id/relativeLayout"
android:weightSum="1">
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/button"/>
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/button2"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"/>
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/button3"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/button4"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>

Try this code. I used two linear layouts instead of one relative layout
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="match_parent">
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:text="TextView"
android:textAlignment="center"
android:textSize="30sp" />
<LinearLayout
android:orientation="horizontal"
android:id="#+id/relativeLayout"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1">
<Button
android:id="#+id/button"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:text="Button" />
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:text="Button" />
</LinearLayout>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
>
<Button
android:id="#+id/button3"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:text="Button" />
<Button
android:id="#+id/button4"
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="match_parent"
android:text="Button" />
</LinearLayout>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:layout_marginTop="10dp"
android:text="TextView"
android:textAlignment="center"
android:textSize="30sp" />
<LinearLayout
android:id="#+id/relativeLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:orientation="horizontal">
<Button
android:id="#+id/button"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:padding="5dp"
android:text="Button" />
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:padding="5dp"
android:text="Button" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:orientation="horizontal">
<Button
android:id="#+id/button3"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:padding="5dp"
android:text="Button" />
<Button
android:id="#+id/button4"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:padding="5dp"
android:text="Button" />
</LinearLayout>
</LinearLayout>
</LinearLayout>

Android Linear Layout Suggestion

How do I get buttons to lay on the screen most optimally distributed and centered on the screen as follows:
The nearest I am able to get is this:
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:orientation="horizontal"
>
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_weight="1"
android:text="Button1" />
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button2" />
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button3" />
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button4" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:text="Button5"
android:layout_weight="1"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button6"
android:layout_weight="1"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button7"
android:layout_weight="1"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Button8"
android:layout_weight="1"/>
</LinearLayout>

Use a relativeLayout for the 3 linearLayouts.
To place the 3 linears below eachother use:
android:layout_below="#+id/linearLayout1"
and
android:layout_below="#+id/linearLayout2"
To center the linears use:
android:layout_centerInParent="true"
android:layout_gravity="center_vertical"
That will give you something like this:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<LinearLayout
android:id="#+id/linearLayout2"
android:layout_below="#+id/linearLayout1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:layout_gravity="center_vertical" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button5" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button6" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button7" />
</LinearLayout>
<LinearLayout
android:id="#+id/linearLayout3"
android:layout_below="#+id/linearLayout2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:layout_gravity="center_vertical" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button8" />
</LinearLayout>
<LinearLayout
android:id="#+id/linearLayout1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button1" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button2" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button3" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Button4" />
</LinearLayout>
Unfortunately it is not showing the last line which is </RelativeLayout>

emulator output different from layout view in android

In the layout view my calculator program looks like this
But when I run my program, it looks like this
Why is this happening?
This is the layout file code:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="#+id/button0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:text="#string/button_0"
android:onClick="onClkBn0" />
<Button
android:id="#+id/button_dot"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button0"
android:layout_alignParentBottom="true"
android:layout_toRightOf="#+id/button0"
android:text="#string/button_dot"
android:onClick="onClkBnDot"/>
<Button
android:id="#+id/button_res"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button0"
android:layout_alignParentBottom="true"
android:layout_toRightOf="#+id/button_dot"
android:text="#string/button_res"
android:onClick="onClkBnRes"/>
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_above="#+id/button0"
android:text="#string/button_1"
android:onClick="onClkBn1"/>
<Button
android:id="#+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button1"
android:layout_alignBottom="#+id/button1"
android:layout_toRightOf="#+id/button1"
android:layout_above="#+id/button_dot"
android:text="#string/button_2"
android:onClick="onClkBn2"/>
<Button
android:id="#+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/button2"
android:layout_toRightOf="#+id/button2"
android:layout_above="#+id/button_res"
android:text="#string/button_3"
android:onClick="onClkBn3"/>
<Button
android:id="#+id/button4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/button1"
android:layout_alignLeft="#+id/button1"
android:text="#string/button_4"
android:onClick="onClkBn4"/>
<Button
android:id="#+id/button5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/button4"
android:layout_alignLeft="#+id/button2"
android:text="#string/button_5"
android:onClick="onClkBn5"/>
<Button
android:id="#+id/button6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/button5"
android:layout_alignLeft="#+id/button3"
android:text="#string/button_6"
android:onClick="onClkBn6"/>
<Button
android:id="#+id/button7"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/button4"
android:layout_alignLeft="#+id/button4"
android:text="#string/button_7"
android:onClick="onClkBn7"/>
<Button
android:id="#+id/button8"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button7"
android:layout_alignBottom="#+id/button7"
android:layout_toRightOf="#+id/button4"
android:text="#string/button_8"
android:onClick="onClkBn8"/>
<Button
android:id="#+id/button9"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/button6"
android:layout_alignLeft="#+id/button6"
android:text="#string/button_9"
android:onClick="onClkBn9"/>
<Button
android:id="#+id/button_plus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button_res"
android:layout_alignBottom="#+id/button_res"
android:layout_toRightOf="#+id/button_res"
android:text="#string/button_plus"
android:onClick="onClkBnPlus"/>
<Button
android:id="#+id/button_minus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/button_plus"
android:layout_alignLeft="#+id/button_plus"
android:text="#string/button_minus"
android:onClick="onClkBnMinus"/>
<Button
android:id="#+id/button_mul"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/button_minus"
android:layout_below="#+id/button9"
android:text="#string/button_mult"
android:onClick="onClkBnMult"/>
<Button
android:id="#+id/button_div"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/button9"
android:layout_alignLeft="#+id/button_mul"
android:text="#string/button_div"
android:onClick="onClkBnDiv"/>
<Button
android:id="#+id/button_can"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="#+id/button_div"
android:layout_centerVertical="true"
android:text="#string/button_cancel"
android:onClick="onClkBnCan"/>
<TextView
android:id="#+id/mantissa"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/button_can"
android:layout_alignParentLeft="true"
android:gravity="right"
android:text="#string/mantissa_default"
android:textIsSelectable="true"
android:textSize="30.0sp" />
<Button
android:id="#+id/button_off"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/mantissa"
android:layout_above = "#+id/button9"
android:layout_alignLeft="#+id/button9"
android:layout_toRightOf="#+id/button_can"
android:onClick="onClkBnOff"
android:text="#string/button_off" />
</RelativeLayout>

Your emulator is doing what you ask. This code :
android:layout_centerVertical="true"
puts the "c" button in the middle of the view, vertically. Then your mantissa view sits atop that view because of this:
android:layout_above="#+id/button_can"
Your off button is coerced into stretching from the mantissa view down to button_9 because of these lines:
android:layout_below="#+id/mantissa"
android:layout_above = "#+id/button9"
Here is one solution that should work for you:
<Button
android:id="#+id/button_can"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="#id/button_div"
android:layout_above="#id/button_div"
android:text="#string/button_cancel"
android:onClick="onClkBnCan"/>
<TextView
android:id="#+id/mantissa"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="#id/button_can"
android:layout_alignParentLeft="true"
android:gravity="right"
android:text="#string/mantissa_default"
android:textIsSelectable="true"
android:textSize="30.0sp" />
<Button
android:id="#+id/button_off"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above = "#id/button9"
android:layout_alignLeft="#id/button9"
android:layout_toRightOf="#id/button_can"
android:onClick="onClkBnOff"
android:text="#string/button_off" />
Also, you should only use the + in strings like "#+id/button9" on the first use of that label. Subsequent references for it would be "#id/button9"

I think you should better use a couple of LinearLayout to get the aspect you want.
Thanks to android:layout_weight you will be able to have the same layout aspect on several screen sizes and density.
Here is a code example showing what you want, the way you want on several screen sizes/devices density:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:id="#+id/mantissa"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:gravity="right"
android:text="#string/mantissa_default"
android:textIsSelectable="true"
android:textSize="30.0sp" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentBottom="true"
android:layout_below="#+id/mantissa"
android:orientation="vertical" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.25"
android:orientation="horizontal" >
<View
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25" />
<View
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25" />
<Button
android:id="#+id/button_off"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnOff"
android:text="#string/button_off" />
<Button
android:id="#+id/button_can"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnCan"
android:text="#string/button_cancel" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.25"
android:orientation="horizontal" >
<Button
android:id="#+id/button7"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn7"
android:text="#string/button_7" />
<Button
android:id="#+id/button8"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn8"
android:text="#string/button_8" />
<Button
android:id="#+id/button9"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn9"
android:text="#string/button_9" />
<Button
android:id="#+id/button_div"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnDiv"
android:text="#string/button_div" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.25"
android:orientation="horizontal" >
<Button
android:id="#+id/button4"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn4"
android:text="#string/button_4" />
<Button
android:id="#+id/button5"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn5"
android:text="#string/button_5" />
<Button
android:id="#+id/button6"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn6"
android:text="#string/button_6" />
<Button
android:id="#+id/button_mul"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnMult"
android:text="#string/button_mult" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.25"
android:orientation="horizontal" >
<Button
android:id="#+id/button1"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_above="#+id/button0"
android:layout_weight="0.25"
android:onClick="onClkBn1"
android:text="#string/button_1" />
<Button
android:id="#+id/button2"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_above="#+id/button_dot"
android:layout_weight="0.25"
android:onClick="onClkBn2"
android:text="#string/button_2" />
<Button
android:id="#+id/button3"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn3"
android:text="#string/button_3" />
<Button
android:id="#+id/button_minus"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnMinus"
android:text="#string/button_minus" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.25"
android:orientation="horizontal" >
<Button
android:id="#+id/button0"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBn0"
android:text="#string/button_0"/>
<Button
android:id="#+id/button_dot"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnDot"
android:text="#string/button_dot" />
<Button
android:id="#+id/button_res"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnRes"
android:text="#string/button_res"/>
<Button
android:id="#+id/button_plus"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="0.25"
android:onClick="onClkBnPlus"
android:text="#string/button_plus" />
</LinearLayout>
</LinearLayout>
</RelativeLayout>

How to stretch the component to match the width of parent components in Android layout?

Below is the layout I designed.
Here is my code:
<LinearLayout
android:id="#+id/digitRow1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="#string/login_button_1" />
<Button
android:id="#+id/button2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="#string/login_button_2" />
<Button
android:id="#+id/button3"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="#string/login_button_3" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_4" />
<Button
android:id="#+id/button5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_5" />
<Button
android:id="#+id/button6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_6" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button7"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_7" />
<Button
android:id="#+id/button8"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_8" />
<Button
android:id="#+id/button9"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_9" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/buttonClear"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_clear" />
<Button
android:id="#+id/button0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_0" />
<Button
android:id="#+id/buttonBack"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_back" />
</LinearLayout>
<LinearLayout
android:id="#+id/buttonRow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:orientation="horizontal"
android:padding="5dp" >
<Button
android:id="#+id/buttonChange"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_dhange" />
<Button
android:id="#+id/buttonDisable"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/login_button_disable" />
</LinearLayout>
The problem is that I want to stretch the bottom two buttons, "Change" and "Back", to match the width of the buttons above.

You can use weight on both of them, like this:
<LinearLayout
android:id="#+id/buttonRow"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:orientation="horizontal"
android:padding="5dp" >
<Button
android:id="#+id/buttonChange"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="#string/login_button_dhange" />
<Button
android:id="#+id/buttonDisable"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="#string/login_button_disable" />

You probably want something like the code below.
I used a hard coded button width, but you probably want to put this in dimen.xml and reference it. I centered everything with gravity.
I tried this with weights as well, but the re-sizing is funny. As your screen gets wider the buttons get two wide.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:gravity="center_horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:id="#+id/digitRow1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button1"
android:layout_width="100dp"
android:layout_height="match_parent"
android:text="1" />
<Button
android:id="#+id/button2"
android:layout_width="100dp"
android:layout_height="match_parent"
android:text="2" />
<Button
android:id="#+id/button3"
android:layout_width="100dp"
android:layout_height="match_parent"
android:text="3" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button4"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="4" />
<Button
android:id="#+id/button5"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="5" />
<Button
android:id="#+id/button6"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="6" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/button7"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="7" />
<Button
android:id="#+id/button8"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="8" />
<Button
android:id="#+id/button9"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="9" />
</LinearLayout>
<LinearLayout
android:id="#+id/digitRow4"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="horizontal" >
<Button
android:id="#+id/buttonClear"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="Clear" />
<Button
android:id="#+id/button0"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="0" />
<Button
android:id="#+id/buttonBack"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="Back" />
</LinearLayout>
<LinearLayout
android:id="#+id/buttonRow"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:orientation="horizontal"
android:padding="5dp"
android:gravity="center_horizontal"
>
<Button
android:id="#+id/buttonChange"
android:layout_width="150dp"
android:layout_height="wrap_content"
android:text="Change" />
<Button
android:id="#+id/buttonDisable"
android:layout_width="150dp"
android:layout_height="wrap_content"
android:text="Disable" />
</LinearLayout>

Try to use weight like below. Also use margins to tweak the positions of the buttons.
<LinearLayout
android:id="#+id/buttonRow"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:orientation="horizontal"
android:padding="5dp" >
<Button
android:id="#+id/buttonChange"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="#string/login_button_dhange" />
<Button
android:id="#+id/buttonDisable"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="#string/login_button_disable" />

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

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