Android中使用ViewStub提高布局性能

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<?xml version="1.0" encoding="utf-8"?>
<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"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.droidyue.viewstubsample.MainActivity">

<Button
android:id="@+id/clickMe"
android:text="Hello World!"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>

<ViewStub
android:id="@+id/myViewStub"
android:inflatedId="@+id/myInflatedViewId"
android:layout="@layout/include_merge"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/clickMe"
/>
</RelativeLayout>

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ViewStub myViewStub = (ViewStub)findViewById(R.id.myViewStub);
if (myViewStub != null) {
myViewStub.inflate();
//或者是下面的形式加载
//myViewStub.setVisibility(View.VISIBLE);
}

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<merge xmlns:android="http://schemas.android.com/apk/res/android">

<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Yes"/>

<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="No"/>

</merge>

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E AndroidRuntime: android.view.InflateException: Binary XML file line #1: <merge /> can be used only with a valid ViewGroup root and attachToRoot=true
E AndroidRuntime:         at android.view.LayoutInflater.inflate(LayoutInflater.java:551)
E AndroidRuntime:         at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
E AndroidRuntime:         at android.view.ViewStub.inflate(ViewStub.java:259)
E AndroidRuntime:         at com.droidyue.viewstubsample.MainActivity$1.onClick(MainActivity.java:20)
E AndroidRuntime:         at android.view.View.performClick(View.java:5697)
E AndroidRuntime:         at android.widget.TextView.performClick(TextView.java:10815)
E AndroidRuntime:         at android.view.View$PerformClick.run(View.java:22526)
E AndroidRuntime:         at android.os.Handler.handleCallback(Handler.java:739)
E AndroidRuntime:         at android.os.Handler.dispatchMessage(Handler.java:95)
E AndroidRuntime:         at android.os.Looper.loop(Looper.java:158)
E AndroidRuntime:         at android.app.ActivityThread.main(ActivityThread.java:7237)
E AndroidRuntime:         at java.lang.reflect.Method.invoke(Native Method)
E AndroidRuntime:         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
E AndroidRuntime:         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
E AndroidRuntime: Caused by: android.view.InflateException: <merge /> can be used only with a valid ViewGroup root and attachToRoot=true
E AndroidRuntime:         at android.view.LayoutInflater.inflate(LayoutInflater.java:491)
E AndroidRuntime:         ... 13 more

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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<include layout="@layout/merge_layout"/>
</LinearLayout>

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/**
* When visibility is set to {@link #VISIBLE} or {@link #INVISIBLE},
* {@link #inflate()} is invoked and this StubbedView is replaced in its parent
* by the inflated layout resource.
*
* @param visibility One of {@link #VISIBLE}, {@link #INVISIBLE}, or {@link #GONE}.
*
* @see #inflate()
*/
@Override
public void setVisibility(int visibility) {
if (mInflatedViewRef != null) {
View view = mInflatedViewRef.get();
if (view != null) {
view.setVisibility(visibility);
} else {
throw new IllegalStateException("setVisibility called on un-referenced view");
}
} else {
super.setVisibility(visibility);
if (visibility == VISIBLE || visibility == INVISIBLE) {
inflate();
}
}
}

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/**
* Inflates the layout resource identified by {@link #getLayoutResource()}
* and replaces this StubbedView in its parent by the inflated layout resource.
*
* @return The inflated layout resource.
*
*/
public View inflate() {
final ViewParent viewParent = getParent();

if (viewParent != null && viewParent instanceof ViewGroup) {
if (mLayoutResource != 0) {
final ViewGroup parent = (ViewGroup) viewParent;
final LayoutInflater factory = LayoutInflater.from(mContext);
final View view = factory.inflate(mLayoutResource, parent,
false);

if (mInflatedId != NO_ID) {
view.setId(mInflatedId);
}

final int index = parent.indexOfChild(this);
parent.removeViewInLayout(this);

final ViewGroup.LayoutParams layoutParams = getLayoutParams();
if (layoutParams != null) {
parent.addView(view, index, layoutParams);
} else {
parent.addView(view, index);
}

mInflatedViewRef = new WeakReference<View>(view);

if (mInflateListener != null) {
mInflateListener.onInflate(this, view);
}

return view;
} else {
throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
}
} else {
throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
}
}