Android performance Optimization Four layouts optimize the use of merge tags

Small white: Previously shared the use of Viewstub tags, Android and other ways to optimize the layout?

Small black: <merge/> Tags are used to reduce the level of the view tree to optimize the Android layout. Let's start with an example to illustrate:

First, the master needs a configuration file Activity_main.xml

<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" > < Textview  Android:layout_width= "Wrap_content"  Span class= "indent" > android:layout_height= "Wrap_content"   android:text= "Merge tag uses"/></RELATIVELAYOUT>      

One more simple activity, file name Mainactivity.java

Package com.example.merge; import android.app.Activity; import Android.os.Bundle; super.oncreate (savedinstancestate); Setcontentview (R.layout.activity_main);}}  

Small white: Create the project according to the code above, and use the "DDMS-and-Dump View Hierarchy for UI Automator" tool after running, as follows

Merge before use

Little black: The bottom two layers relativelayout and TextView are the contents of the Activity_main.xml layout, the framelayout above is the top view added by activity Setcontentview. Use the Merge tab below to see the difference

The layout file Activity_main.xml modified as follows:

<merge 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" > < Textview  Android:layout_width= "Wrap_content"  Span class= "indent" > android:layout_height= "Wrap_content"   android:text= "Merge tag uses"/></MERGE>        

Small white: Use the DDMS, Dump View Hierarchy for UI Automator tool, as follows

After the merge is used

Small black: Framelayout below is directly textview, compared with the previous one layer relativelayout and achieve the same effect.

At some point, a custom reusable layout contains too many levels of labels, such as our

For example, if you use <include> to include the above layout, the system automatically ignores the merge level, and the two buttons are placed directly with the include peer

Small white: What is the case for using the merge tag?

Black: One is like the above example, the child view does not need to specify any layout properties for the parent view, in the example TextView just needs to be added directly to the parent view for display on the line.

The other is that if you need to embed a layout (or view) inside the LinearLayout, and the root node of the layout (or view) is also linearlayout, so that there is a layer of unused nesting, it is no doubt that this only slows down the program speed. And at this point, if we use the merge root tag to avoid that problem, the official document Android Layout Tricks #3: Optimize by the example in merging demonstrates this situation.

Small white: <merge/> Label What's the limit?

Black: <merge/> can only be used as the root tag of an XML layout. When you inflate a layout file that begins with <merge/>, you must specify a parent ViewGroup, and you must set Attachtoroot to True.

Black: The merge tag also has some properties to use to view API documentation such as Android:layout_width, android:layout_height, etc.

Android performance Optimization Four layouts optimize the use of the merge label