The merge tag

The merge tag allows you to avoid an unnecessary use of nested layouts when you use the include tag.
Consider the following example that consists of 3 files .xml as layout:

• activity_main.xml
  
  XHTML

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="row 1" /> <include layout="@layout/merge_1_level"/> </LinearLayout>

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  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical" >       <TextView         android:id="@+id/textView1"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="row 1" />       <include layout="@layout/merge_1_level"/>      </LinearLayout>

  
  this file .xml creates a vertical LinearLayout with a TextView inside and the contents of the file merge_1_level.xml using the include tag
• merge_1_level.xml
  
  XHTML

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/textView2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="row 2" /> <include layout="@layout/merge_2_level" /> </LinearLayout>

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  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical" >       <TextView         android:id="@+id/textView2"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="row 2" />       <include layout="@layout/merge_2_level" />   </LinearLayout>

  
  This file adds another TextView and the contents of the file merge_2_level.xm using the include tag
• merge_2_level.xml
  
  XHTML

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/textView3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="row 3" /> </LinearLayout>

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  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical" >       <TextView         android:id="@+id/textView3"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="row 3" />   </LinearLayout>

  
  this file adds the last TextView

The final result in the emulator is as follows:

The resulting layout is equivalent to:

As you can see the nested LinearLayouts are useless and redundant, to optimize the code you can use the merge tag in the included files: merge_1_level.xml and merge_2_level.xml

• merge_1_level.xml
  
  XHTML

  <merge xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" > <TextView android:id="@+id/textView2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="row 2" /> <include layout="@layout/merge_2_level" /> </merge>

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  <merge xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent" >       <TextView         android:id="@+id/textView2"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="row 2" />       <include layout="@layout/merge_2_level" />   </merge>

• merge_2_level.xml
  
  XHTML

  <merge xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" > <TextView android:id="@+id/textView3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="row 3" /> </merge>

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  <merge xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent" >       <TextView         android:id="@+id/textView3"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="row 3" />   </merge>

In this way the resulting layout is equivalent to: