Develop Reference

Positionning a image to the top of screen with ContraintLayout

i looking to align to the top of screen a simple image with ConstraintLayout. I just tried:
<ImageView
android:id="#+id/imagecookie"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="#drawable/before_cookie"
app:layout_constraintTop_toBottomOf="parent" />
The pict is positionning in the middle of screen.
Any help?
Thanks

You're setting the top of your ImageView to the bottom of the parent (ConstraintLayout), you need to set it to the top
EDIT Sample with the whole layout
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:background="#color/colorPrimary"
tools:context=".MainActivity">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#mipmap/ic_launcher"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Result

Thank for you time and help but it still not positioned at the top of screen.
i put my picture at the top of the screen (and middle horizontal) with:
<ImageView
android:id="#+id/imagecookie"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/suzuki"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />

How to anchor a Button on a View in the center

I'm trying to accomplish the following:
enter image description here
The gray part is the background of the activity and the white part is a horizontal LinearLayout. I want to create the spinner overlapping the top border of the LinearLayout but everything I can do is put it inside the layout or on top of it. Is there a way to accomplish this? or a workaround?

We can use ConstraintLayout for this. We need to use combinations of two properties
layout_constraintTop_toBottomOf
layout_constraintBottom_toBottomOf
This will center the Button or any other View
Example:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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">
<View
android:id="#+id/topView"
android:layout_width="match_parent"
android:layout_height="100dp"
android:background="#android:color/holo_orange_dark"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
android:orientation="horizontal" />
<View
android:id="#+id/bottomView"
android:layout_width="match_parent"
android:layout_height="100dp"
app:layout_constraintTop_toBottomOf="#id/topView"
android:background="#android:color/holo_green_light"
android:orientation="horizontal" />
<com.google.android.material.button.MaterialButton
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintTop_toBottomOf="#id/topView" // this
app:layout_constraintBottom_toBottomOf="#id/topView" // and this is important, it aligns the view to the top view
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
Result:

Is there a way to center an element while enforcing it stays on screen in Android?

For the sake of simplicity, let's say I've got two text views A and B. A is a set size with a set margin between it and the parent. B is a variable size.
The goal is to position B centered below A if it fits but not have B go off the screen.
Here's the xml I've currently got for the two elements:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".MainActivity">
<TextView
android:id="#+id/element_A"
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_marginTop="12dp"
android:layout_marginEnd="12dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:text="elem_A"/>
<TextView
android:id="#+id/element_B"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="#id/element_A"
app:layout_constraintEnd_toEndOf="#id/element_A"
app:layout_constraintTop_toBottomOf="#id/element_A"
android:text="sml"/>
</androidx.constraintlayout.widget.ConstraintLayout>
The image below shows three figures: left is what I'm seeing when element B is small enough (great), middle is what I'm seeing when element B is too big (not good), and right is what I want to see when element B is too big.
As it turns out, switching from ConstraintLayout to LinearLayout actually fixes this problem. I'm still curious if this is possible using ConstraintLayout but for now I'll just use LinearLayout.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
android:layout_marginTop="12dp"
android:layout_marginEnd="12dp"
android:layout_gravity="end"
tools:context=".MainActivity">
<TextView
android:id="#+id/element_A"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="end"
android:gravity="end"
android:layout_weight="1"
android:text="elem_A"/>
<TextView
android:id="#+id/element_B"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:layout_weight="1"
android:text="much much longer element B"/>
</LinearLayout>

First create LinearLayout and set orientation to horizontal And again you need to create child LinearLayout and wrap both text feilds into it and set it's layout_gravity to right also set orientation to vertical. After that you need to distribute weight of LinearLayout into both of text feilds equally and also set gravity and layout_gravity to center for both text feilds . Tip :- don't use hard-coded values,instead use match_parent / wrap_content for all elements.

I have made changes to your code, cop-paste all code to your xml file...
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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"
tools:context=".MainActivity">
<TextView
android:id="#+id/element_A"
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_marginTop="32dp"
android:text="elem_A"
android:textAlignment="center"
app:layout_constraintEnd_toEndOf="#+id/element_B"
app:layout_constraintStart_toStartOf="#+id/element_B"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/element_B"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="32dp"
android:text="sml"
android:textAlignment="center"
app:layout_constraintEnd_toEndOf="parent"
tools:layout_editor_absoluteY="88dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

Constraint Layout does'nt constraint nested elements of other layouts

I'm trying to create a layout of a list which starts on the bottom of a button and it's 3/4 of screen's width.
Just like this:
First, I used nested Linear layouts a horizonal and a vertical one, but then I read here that Constraint layouts are more responsive and I was impressed and gave it a try.
So, I tried to replace the outer layout to a constraint layout but now, I can't constraint the list to start at the bottom of the button and it starts at top of the screen.
I tried to see what would happen if I replaced the whole linear layout with a button just to see that the attributes are correctly implemented and it worked, so I understood that the Constraint layout does'nt effect the sons of the Linear layout although it should be effecting the whole layout (as I see it).
my code is the following:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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"
tools:context=".MainActivity">
<ImageButton
android:id="#+id/settings_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="#FFFFFF"
android:src="#drawable/ic_menu_black_32dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<LinearLayout
android:id="#+id/list_linear_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="4"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toStartOf="#+id/settings_button"
app:layout_constraintTop_toBottomOf="#+id/settings_button">
<ListView
android:id="#+id/listview"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="3" />
</LinearLayout>
</android.support.constraint.ConstraintLayout>
My current layout looks like this:
I really appriciate the helpers!

You need to change layout height of linear layout to 0dp, I will put here the layout for you. Also consider migrating to androidx :)
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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">
<ImageButton
android:id="#+id/settings_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="#FFFFFF"
android:src="#drawable/ic_menu_black_32dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<LinearLayout
android:id="#+id/list_linear_layout"
android:layout_width="match_parent"
android:layout_height="0dp"
android:weightSum="4"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/settings_button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/settings_button">
<ListView
android:id="#+id/listview"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="3" />
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

I think, that using match_parent as width or height of child and adding any constraint is wrong here.
Edited xml (change margins if you want):
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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"
tools:context=".MainActivity">
<ImageButton
android:id="#+id/settings_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="24dp"
android:layout_marginTop="24dp"
android:backgroundTint="#FFFFFF"
android:src="#drawable/ic_menu_black_32dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<LinearLayout
android:id="#+id/list_linear_layout"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="24dp"
app:layout_constrainedWidth="true"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="#+id/settings_button"
app:layout_constraintTop_toBottomOf="#+id/settings_button"
app:layout_constraintWidth_percent="0.75">
<ListView
android:id="#+id/listview"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="3"/>
</LinearLayout>

Android layout place a layout in the middle of another two layouts

Hello I have to create the UI like bellow,(picture attached) using regular Android layouts. I got header, footer and middle areas along with a image view.
According to the picture : Area A and Area C is similar height (20% of screen) and image view should be placed always in the middle of Area B and Area C.
My current xml code is like this
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
>
<LinearLayout
android:id="#+id/show_contact_bottomArea"
android:layout_width="match_parent"
android:layout_height="120dp"
android:orientation="vertical"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true">
</LinearLayout>
<LinearLayout
android:id="#+id/show_contact_middleArea"
android:layout_width="match_parent"
android:layout_height="150dp"
android:orientation="vertical"
android:background="#color/grayContact"
android:layout_below="#+id/show_contact_headerArea"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_above="#+id/show_contact_bottomArea">
</LinearLayout>
<LinearLayout
android:id="#+id/show_contact_headerArea"
android:layout_width="match_parent"
android:layout_height="120dp"
android:orientation="vertical"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"></LinearLayout>
<ImageView
android:layout_width="150dp"
android:layout_height="150dp"
app:srcCompat="#drawable/common_google_signin_btn_icon_dark_focused"
android:id="#+id/imageView2"
android:layout_marginBottom="40dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
I gave
marginBottom="40dp"
for image view to push it upwards, which is not a good practice. what is the best way to place the image view in the center of Area B's and Area C's border.
Also currently I gave
android:layout_height="120dp"
for Area A & Area B's height but ideally both should be 20%(each) of the screen, how to achieve that also?

You can give weights 20 % to each A and C. This way they will occupy 20% of top and bottom respectively. Assign rest 60% of height to B.
For imageView, you can place entire layout in Coordinate layout and assign anchor to footer.
Her is code snippet
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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">
<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:weightSum="10">
<LinearLayout
android:id="#+id/show_contact_bottomArea"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_weight="2"
android:background="#color/primary_light"
android:orientation="vertical">
</LinearLayout>
<LinearLayout
android:id="#+id/show_contact_middleArea"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_above="#+id/show_contact_bottomArea"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="#+id/show_contact_headerArea"
android:layout_weight="6"
android:background="#color/holo_blue_light"
android:orientation="vertical">
</LinearLayout>
<LinearLayout
android:id="#+id/show_contact_headerArea"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_weight="2"
android:background="#color/primary"
android:orientation="vertical"></LinearLayout>
</LinearLayout>
<ImageView
android:id="#+id/imageView2"
android:layout_width="150dp"
android:layout_height="150dp"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="40dp"
app:layout_anchor="#+id/show_contact_headerArea"
app:layout_anchorGravity="center_horizontal|top"
app:srcCompat="#drawable/header_record" />
</android.support.design.widget.CoordinatorLayout>
Result :- I have colored different section with different color code.

use weight for giving exact portion of Area and Frame Layout
for eg:
weight sum =4 have to give in parent Linear layout
Area A give 1
Area b give 2
Area c give 1
After Area B add image View with top -(height you want to appear in B's portion)