我似乎无法把握为什么发生这种情况。这code：

I can't seem to grasp why this is happening. This code:

mProgressDialog = ProgressDialog.show(this, "", getString(R.string.loading), true);

工作得很好。然而，这code：

works just fine. However, this code:

mProgressDialog = ProgressDialog.show(getApplicationContext(), "", getString(R.string.loading), true);

抛出以下异常：

throws the following exception:

W/WindowManager(  569): Attempted to add window with non-application token WindowToken{438bee58 token=null}.  Aborting.
D/AndroidRuntime( 2049): Shutting down VM
W/dalvikvm( 2049): threadid=3: thread exiting with uncaught exception (group=0x4001aa28)
E/AndroidRuntime( 2049): Uncaught handler: thread main exiting due to uncaught exception
E/AndroidRuntime( 2049): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tastekid.TasteKid/com.tastekid.TasteKid.YouTube}: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
E/AndroidRuntime( 2049):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
E/AndroidRuntime( 2049):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
E/AndroidRuntime( 2049):    at android.app.ActivityThread.access$2100(ActivityThread.java:116)
E/AndroidRuntime( 2049):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
E/AndroidRuntime( 2049):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 2049):    at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 2049):    at android.app.ActivityThread.main(ActivityThread.java:4203)
E/AndroidRuntime( 2049):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 2049):    at java.lang.reflect.Method.invoke(Method.java:521)
E/AndroidRuntime( 2049):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
E/AndroidRuntime( 2049):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
E/AndroidRuntime( 2049):    at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime( 2049): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
E/AndroidRuntime( 2049):    at android.view.ViewRoot.setView(ViewRoot.java:460)
E/AndroidRuntime( 2049):    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:177)
E/AndroidRuntime( 2049):    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
E/AndroidRuntime( 2049):    at android.app.Dialog.show(Dialog.java:238)
E/AndroidRuntime( 2049):    at android.app.ProgressDialog.show(ProgressDialog.java:107)
E/AndroidRuntime( 2049):    at android.app.ProgressDialog.show(ProgressDialog.java:90)
E/AndroidRuntime( 2049):    at com.tastekid.TasteKid.YouTube.onCreate(YouTube.java:45)
E/AndroidRuntime( 2049):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
E/AndroidRuntime( 2049):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
E/AndroidRuntime( 2049):    ... 11 more

任何想法，为什么发生这种情况？我从的onCreate 方法调用此。

推荐答案

哪个版本的API您使用的？如果我是对的什么问题，然后这是固定的Andr​​oid 1.6（API版本4）。

Which API version are you using? If I'm right about what the problem is then this was fixed in Android 1.6 (API version 4).

它看起来像对象引用 getApplicationContext（）是只返回指向空。我觉得你有类似的一个问题，我在这部分的code。在的onCreate（）正在运行的窗口前实际完成的是建成。这将是一个黑客，但尽量在几百毫秒启动一个新的线程（IIRC：300-400似乎为我工作，但你需要修补），打开你的ProgressDialog并开始其他任何你需要（例如，网络IO）。事情是这样的：

It looks like the object reference that getApplicationContext() is returning just points to null. I think you're having a problem similar to one I had in that some of the code in the onCreate() is being run before the window is actually done being built. This is going to be a hack, but try launching a new Thread in a few hundred milliseconds (IIRC: 300-400 seemed to work for me, but you'll need to tinker) that opens your ProgressDialog and starts anything else you needed (eg. network IO). Something like this:

@Override
public void onCreate(Bundle savedInstanceState) {
    // do all your other stuff here

    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            mProgressDialog = ProgressDialog.show(
               YouTube.this.getApplicationContext(), "",
               YouTube.this.getString(R.string.loading), true);

            // start time consuming background process here
        }
    }, 1000); // starting it in 1 second
}