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" android:layout_height= "Wrap_content " android:text= "Merge label use"/></relativelayout>
One more simple activity, file name Mainactivity.java
Package Com.example.merge;import Android.app.activity;import Android.os.bundle;public class MainActivity extends Activity { @Override protected void onCreate (Bundle savedinstancestate) { 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" android:layout_height= "Wrap_content " android:text= "Merge label use"/></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, so you can view the API documentation, such asAndroid:layout_width,Android:layout_height, etc.
References:re-using Layouts with <include/>android Layout Tricks #2: Reusing Layoutsinclude and merge tags use examples
Android layout Tricks #3: Optimize by merging "Android Application performance Optimization" 8th. Optimization of graphic performance optimization of the merge source code
for more optimization related articles, see:Android Basic Learning Article Summary"Part III performance optimization
