Develop Reference

How can I center a linear layout to the middle of its parent?

I am in the process of writing my first full Android app, and I want to center a linear layout so that the layout itself is centered, not just the content inside of the layout. I have seen through old posts that android:layout_gravity is used to do this, but as I enter that into my activity's XML, there are no suggestions, and nothing happens when fully entered.
Am I not supposed to use a linear layout to achieve this? Am I supposed to make its size match_parent and just constrain the sizes of all of its children? My idea for the layout was to constrain the size of the linear layout, center it, and have all of its children's horizontal size match_parent.
Here is my activity's XML for reference:
<?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="com.frc5113.combustiblescouting.MainActivity">
<LinearLayout
android:layout_width="140dp"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Team Number" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="Color" />
</LinearLayout>

Your root layout is a ConstraintLayout. I don't think that supports the attribute layout_gravity. You should either use LinearLayout or use constraints relative to your root view as described here.

Try this, it makes your containt horizontal & vertical center simultaneously:
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.frc5113.combustiblescouting.MainActivity"
android:orientation="vertical"
android:gravity="center">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Team Number" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:hint="Color" />
</LinearLayout>

using android:gravity="center" on the LinearLayout will center it's childs not itself.
There would be the android:layout_gravity attribute which is telling the parent how this child wants to be layed out. But this needs to be supported by the Containers' LayoutParams (which is true for e.g. FrameLayout, LinearLayout...)
But Constraintlayout does not support this kind of child gravity.
Here you need to set Constraints on the child (in your case the LinearLayout) in order to place it properly.
Therefore if you want to center the LinearLayout (which would somehow be obsolete as you could center it's childs directly in the ConstraintLayout)
you can achieve this like the following:
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="140dp"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="vertical"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent">
<!-- content -->
</LinearLayout>
</android.support.constraint.ConstraintLayout>

Adding layout to a scrollview gets eaten up

I have a layout something like this:
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginBottom="10dp"
android:background="#ff303f"
android:id="#+id/layout">
<ImageView
android:id="#+id/picture"
android:layout_width="300dp"
android:layout_height="300dp"
android:layout_centerInParent="true"/>
<Button
android:id="#+id/cancel"
android:layout_width="45dp"
android:layout_height="45dp"
android:layout_alignRight="#id/picture"
android:background="#drawable/cross_out"/>
</RelativeLayout>
I inflate it using the usual layout inflator service, set up some functionality to the button and an image to the imageview (all images are of same size and aspect ratio).
After that, I add this view to my fragment's layout which is nothing but a ScrollView which is a parent, it has a child linear layout that I call 'map' and simply add it to the map.
Expected : The added layouts should get added properly and I can scroll through it.
Actual : If more than 2 are added, the first one gets eaten up. I can see it half or sometimes it is completely eaten up. :\
Any idea whats going on here? Thanks a lot for your time.
EDIT:
Here's the layout file I add the inflated layout into:
<?xml version="1.0" encoding="utf-8"?>
<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/scrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#f6ff45">
<LinearLayout
android:id="#+id/map"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#43ff44"
android:orientation="vertical"
android:layout_margin="10dp"
android:layout_gravity="center"
android:layout_marginTop="15dp">
</LinearLayout>
</ScrollView>
I also forgot to mention that after adding 3 or more of these layouts, I realized there's unnecessary empty space in the end. :\

If you have some android:layout_gravity or gravity property in your ScrollView, that may be the reason. Try deleting it, or make it center_horizontal.

Try this code for your layout file;
<?xml version="1.0" encoding="utf-8"?>
<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/scrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#f6ff45">
<LinearLayout
android:id="#+id/map"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#43ff44"
android:orientation="vertical"
android:layout_margin="10dp"
android:layout_gravity="center"
android:layout_marginTop="15dp">
</LinearLayout>
</ScrollView>
As I mentioned before, android:layout_gravity="center"in this LinearLayout causes this problem. Because it doesn't only horizontally center but also verticelly center the contents. It means when they are longer than the available height, the center part will appear. I only changed it into android:layout_gravity="center_horizontal" and the problem is fixed.

Center ListView horizontally

As easy as it seems to be, as stubbornly this ListView won't center itself (or it's content within - doesn't matter to me).
This is activity layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.drobiazko.den.mobineon.MainActivity"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center_horizontal"
android:background="#drawable/bg">
<RelativeLayout android:id="#+id/clock_container"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<!--<RelativeLayout android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#android:color/holo_blue_dark">-->
<com.drobiazko.den.mobineon.ListViewRowsHeight
android:id="#+id/listview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:overScrollMode="never"
android:scrollbars="none"
android:divider="#null"
android:listSelector="#android:color/transparent"
android:persistentDrawingCache="scrolling|animation"
android:background="#android:color/holo_green_dark" />
<!--</RelativeLayout>-->
</LinearLayout>
This is ListView's item layout:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageView android:id="#+id/btn_icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="#style/custom_btn_icon" />
<TextView android:id="#+id/btn_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="#style/custom_btn_name" />
<TextView android:id="#+id/btn_count"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="#style/custom_btn_count" />
</RelativeLayout>
I've tried everything (including simplifying layout to max), but it still won't go.
Funny that the first relative layout clock_container - centers like a charm, due to parent LinearLayout's android:gravity="center_horizontal". Why won't ListView?
Added later:
Inspired by FOliveira's answer, I've done some investigation and found that:
everything works fine, parent LinearLayout has android:gravity="center_horizontal" and centers his children respectfully. The reason for ListView's children are left-aligned is that ListView takes all possible width despite his android:layout_width="wrap_content" attribute.
Anyone knows why is that?

First of all , i would remove the first linear layout and stay only with the relative layout as the parent.
After having the relative layout as the main parent , set the CENTER_IN_PARENT attribute to true.
The mistake you are making is that you are setting the gravity of Linear Layout child to center horizontal, which is correct, but the only children being affected by this option is the Relative layout itself.

Linear and Relative Layout in Android

I want to show a button bar at the end of my activity. I created a layout named: batton_bar_ref.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:background="#drawable/shape_blue_light_horizental_gradiant_notrounded"
android:gravity="center"
android:orientation="vertical"
android:paddingBottom="10dip"
android:paddingTop="10dip" >
<Button
android:id="#+id/pay_button"
android:layout_width="100dip"
android:layout_height="50dip"
android:text="#string/pay"
android:textSize="16sp"
android:textStyle="bold" >
</Button>
</LinearLayout>
</RelativeLayout>
And add it with <include layout="#layout/button_bar_ref"/> to another layout.
It is showing a warning message :
This LinearLayout layout or its RelativeLayout parent is useless; transfer the background attribute to the other view.
Could you let me know how can I fix it?
Addenda :
button bar should be at the end of screen.
Note that Linear layout has a background.

It is just suggestion to optimize your layout by removing tags that are not required. In your case since you do not have any children under RelativeLayout other than LinearLayout, this particular layout is not really correctly designed.
First you can ignore this warning, and once you have successfully designed the layout file in which you are planning to include this layout file, you will realize that one of the layouts declared in this file can be eliminated.

Remove the relative layout.
<?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="wrap_content"
android:layout_alignParentBottom="true"
android:background="#drawable/shape_blue_light_horizental_gradiant_notrounded"
android:gravity="center"
android:orientation="vertical"
android:paddingBottom="10dip"
android:paddingTop="10dip" >
<Button
android:id="#+id/pay_button"
android:layout_width="100dip"
android:layout_height="50dip"
android:text="#string/pay"
android:textSize="16sp"
android:textStyle="bold" >
</Button>
</LinearLayout>

try removing the RelativeLayout tag from the xml file

This warning is triggered, when a Layout has only one child that is also a Layout. In this case one of both can be removed without any problems. It is recommended to remove these redundant layouts as they reduce the overall performance of the UI.
In your case there is no use of RelativeLayout. There will be no change if you remove this. So this warning is showing. But this is just a warning. There is no harm in using this

Please use bellow code fix your issue.
<?xml version="1.0" encoding="utf-8"?>
<Button
android:id="#+id/pay_button"
android:layout_width="100dip"
android:layout_height="50dip"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:gravity="center"
android:text="#string/pay"
android:textSize="16sp"
android:textStyle="bold" >
</Button>

Have ways for remain previous layout in all pages?

I want to create an application that have 5 buttons in bottom of page, when user clicks
on the any button, the page will changes but 5buttons remain in bottom of page. now i create
this program but when i call setContentView() in other class becuase i call other layout,
buttons removed. have ways for remain 5buttons? or i should create 5buttons again in 5layout?
Thanks
Cheers

Easiest and Simple way is to make a layout having 5 buttons and it in all your layout files
Example
<include layout="#layout/titlebar"/>
Or another way is to use fragments so tht only fragments with change keeping other of your layout stuff same
Edit
OR Use the <merge> Tag
The <merge /> tag helps eliminate redundant view groups in your view hierarchy when including one layout within another. For example, if your main layout is a vertical LinearLayout in which two consecutive views can be re-used in multiple layouts, then the re-usable layout in which you place the two views requires its own root view. However, using another LinearLayout as the root for the re-usable layout would result in a vertical LinearLayout inside a vertical LinearLayout. The nested LinearLayout serves no real purpose other than to slow down your UI performance.
To avoid including such a redundant view group, you can instead use the element as the root view for the re-usable layout. For example:
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/add"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/delete"/>
</merge>
Now, when you include this layout in another layout (using the tag), the system ignores the element and places the two buttons directly in the layout, in place of the tag.
Please go through this link to gain more information about Reusing layouts

From what I can gather, I think you are looking for tabs instead of Buttons. Take a look at this.

Thanks for answer. I read developer link and i add merge and include tag to xml file but the program has errors. Why?
MainActivity.xml
<?xml version="1.0" encoding="utf-8"?>
<include layout="#layout/location"/>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<WebView
android:id="#+id/web_view"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1.0" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#color/background"
android:gravity="bottom"
android:orientation="horizontal" >
<Button
android:id="#+id/button_home"
style="?android:attr/borderlessButtonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableTop="#drawable/home_icon"
android:text="#string/button_home"
android:textColor="#color/text_home" />
<Button
android:id="#+id/button_product"
style="?android:attr/borderlessButtonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableTop="#drawable/product_icon"
android:onClick="Product"
android:text="#string/button_product"
android:textColor="#color/text_product" />
<Button
android:id="#+id/button_places"
style="?android:attr/borderlessButtonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableTop="#drawable/places_icon"
android:onClick="Places"
android:text="#string/button_places"
android:textColor="#color/text_places" />
<Button
android:id="#+id/button_rewards"
style="?android:attr/borderlessButtonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableTop="#drawable/rewards_icon"
android:onClick="Rewards"
android:text="#string/button_rewards"
android:textColor="#color/text_rewards" />
<Button
android:id="#+id/button_more"
style="?android:attr/borderlessButtonStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableTop="#drawable/more_icon"
android:onClick="More"
android:text="#string/button_more"
android:textColor="#color/text_more" />
</LinearLayout>
</LinearLayout>
location.xml
<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView>
<com.google.android.maps.MapView
android:id="#+id/mapView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clickable="true"
android:apiKey="0cPRv243zM1_S3ydsNg8MJP9_6BfCp642jOhPvQ"/>
<LinearLayout
android:id="#+id/zoom"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"/>
</LinearLayout>
</merge>
what is incorrect?
Thank you