Android 性能优化 三 布局优化ViewStub标签的使用

<LinearLayout 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:orientation="horizontal" >

    <Button
        android:id="@+id/show_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="显示"/>
   
    <ViewStub
        android:id="@+id/viewstub"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout="@layout/sub_layout"
        />
   
    <Button
        android:id="@+id/hide_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="隐藏"/>
   
</LinearLayout>

<TextView  xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/textview"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:text="ViewStub中包含的TextVeiw"/>

package com.example.viewstub;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewStub;
import android.view.View.OnClickListener;

public class MainActivity extends Activity {

     @Override
     protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
         
          final ViewStub viewStub = (ViewStub) findViewById(R.id.viewstub);
         
          View showButton = findViewById(R.id.show_button);
          showButton.setOnClickListener(new OnClickListener() {
              
               @Override
               public void onClick(View v) {
                    viewStub.inflate();
               }
          });
         
          View hideButton = findViewById(R.id.hide_button);
          hideButton.setOnClickListener(new OnClickListener() {
              
               @Override
               public void onClick(View v) {
                    viewStub.setVisibility(View.GONE);
               }
          });
     }
}

java.lang.IllegalStateException: ViewStub must have a non-null ViewGroup viewParent
     at android.view.ViewStub.inflate(ViewStub.java:287)
     at com.example.viewstub.MainActivity$1.onClick(MainActivity.java:23)
     at android.view.View.performClick(View.java:4475)
     at android.view.View$PerformClick.run(View.java:18786)
     at android.os.Handler.handleCallback(Handler.java:730)
     at android.os.Handler.dispatchMessage(Handler.java:92)
     at android.os.Looper.loop(Looper.java:176)
     at android.app.ActivityThread.main(ActivityThread.java:5419)
     at java.lang.reflect.Method.invokeNative(Native Method)
     at java.lang.reflect.Method.invoke(Method.java:525)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
     at dalvik.system.NativeStart.main(Native Method)