ViewAnimator導致NullPointerException

Question

嘿，我想使用ViewAnimator，我可能缺少一些基本的東西。 這是我有：

 va = new ViewAnimator(this); 
    va.setInAnimation(inFromLeftAnimation()); 
    va.setOutAnimation(outToRightAnimation()); 

    RelativeLayout stage = (RelativeLayout)findViewById(R.layout.american_stage); 
    va.addView(stage,0); 


    setContentView(va); 

凡inFromLeftAnimation和outToRightAnimation公正處理動畫和完美的作品。 而且ofcourse該文件確實存在...... 我得到這個日誌：

07-13 15:45:14.515: E/AndroidRuntime(564): java.lang.RuntimeException: Unable to start activity ComponentInfo{shibby.webhunt/shibby.webhunt.ArcadeModeActivity}: java.lang.NullPointerException 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.os.Looper.loop(Looper.java:123) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread.main(ActivityThread.java:4627) 
07-13 15:45:14.515: E/AndroidRuntime(564): at java.lang.reflect.Method.invokeNative(Native Method) 
07-13 15:45:14.515: E/AndroidRuntime(564): at java.lang.reflect.Method.invoke(Method.java:521) 
07-13 15:45:14.515: E/AndroidRuntime(564): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
07-13 15:45:14.515: E/AndroidRuntime(564): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
07-13 15:45:14.515: E/AndroidRuntime(564): at dalvik.system.NativeStart.main(Native Method) 
07-13 15:45:14.515: E/AndroidRuntime(564): Caused by: java.lang.NullPointerException 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.view.ViewGroup.addView(ViewGroup.java:1815) 
07-13 15:45:14.515: E/AndroidRuntime(564): at shibby.webhunt.ArcadeModeActivity.onCreate(ArcadeModeActivity.java:25) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 

，我不知道爲什麼。 是否不可能使用XML文件作爲視圖？我是否必須自己創建視圖？

Answer 1

07-13 15:45:14.515: E/AndroidRuntime(564): Caused by: java.lang.NullPointerException 
07-13 15:45:14.515: E/AndroidRuntime(564): at android.view.ViewGroup.addView(ViewGroup.java:1815) 

它看起來像你想添加視圖（RelativeLayout stage）是空的，我不相信你可以加載findViewById（）佈局：

findViewById(R.layout.american_stage); 

如果你想開在american_stage.xml不可見的佈局，使用LayoutInflater：

LayoutInflater layoutInflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE); 
stage = layoutInflater.inflate(R.layout.american_stage, null); 

或者如果你試圖加載已經顯現RelativeLayou T：

1）給出的RelativeLayout的的ID american_stage

<RelativeLayout 
    android:id="@+id/american_stage" 
    ... 

2），並使用：

findViewById(R.id.american_stage);