Android ViewAnimator导致NullPointerException

嘿，我正在尝试使用ViewAnimator，我可能缺少一些基本的东西。 这就是我所拥有的：

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

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


    setContentView(va);

其中，InfoRomLeftAnimation和outToRightAnimation只处理动画，效果非常好。 当然，这个文件确实存在。。。 我得到这个日志：

   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)

我不知道为什么。 是否无法将XML文件用作视图？我必须自己构建视图吗

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)

看起来您试图添加的视图（

RelativeLayout stage

）为空，我认为您无法使用findViewById（）加载布局：

如果试图在american_stage.xml中打开不可见的布局，请使用LayoutInflater：

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

或如果您试图加载已可见的RelativeLayout：

1） 在id

american\u stage

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

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

findViewById(R.id.american_stage);