无法显示警报对话框

Question

我无法显示警报对话框。一切都是正确的，直到我设置方法 dialog.show()，然后我无法打开我的应用程序。没有这个方法一切都很好。

我声明了两个全局对象：

AlertDialog.Builder builder;
AlertDialog dialog;

然后在 MainActivity 中，我通过builder构建一个对话框并创建它。

builder = new AlertDialog.Builder(this.getApplicationContext());
        builder.setMessage("We're sorry, but on Your device accelerometer isn't available")
        .setCancelable(false)
        .setPositiveButton("OK", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) 
            {
                MainActivity.this.finish();
            }
        });

        dialog = builder.create();

到目前为止，一切正常，没有任何异常，但是当我想显示对话框时，出现了一些异常，我无法运行此应用程序：

dialog.show();  //this method doesn't work and causes problems

我做错了什么？

编辑： 例外：

06-26 20:49:03.540: D/dalvikvm(4085): GC_FOR_ALLOC freed 38K, 8% free 2499K/2712K, paused 42ms, total 45ms
06-26 20:49:03.580: I/dalvikvm-heap(4085): Grow heap (frag case) to 6.146MB for 3712016-byte allocation
06-26 20:49:03.700: D/dalvikvm(4085): GC_FOR_ALLOC freed 2K, 4% free 6121K/6340K, paused 112ms, total 112ms
06-26 20:49:03.770: D/dalvikvm(4085): GC_CONCURRENT freed <1K, 4% free 6121K/6340K, paused 6ms+16ms, total 71ms
06-26 20:49:04.460: D/gralloc_goldfish(4085): Emulator without GPU emulation detected.
06-26 20:49:42.030: E/Trace(4138): error opening trace file: No such file or directory (2)
06-26 20:49:42.900: D/dalvikvm(4138): GC_FOR_ALLOC freed 41K, 8% free 2499K/2716K, paused 66ms, total 68ms
06-26 20:49:42.940: I/dalvikvm-heap(4138): Grow heap (frag case) to 6.146MB for 3712016-byte allocation
06-26 20:49:43.050: D/dalvikvm(4138): GC_FOR_ALLOC freed 2K, 4% free 6121K/6344K, paused 107ms, total 107ms
06-26 20:49:43.120: D/dalvikvm(4138): GC_CONCURRENT freed <1K, 4% free 6121K/6344K, paused 5ms+5ms, total 70ms
06-26 20:49:43.540: D/dalvikvm(4138): GC_FOR_ALLOC freed 3638K, 53% free 3483K/7300K, paused 36ms, total 37ms
06-26 20:49:43.621: D/AndroidRuntime(4138): Shutting down VM
06-26 20:49:43.630: W/dalvikvm(4138): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
06-26 20:49:43.640: E/AndroidRuntime(4138): FATAL EXCEPTION: main
06-26 20:49:43.640: E/AndroidRuntime(4138): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.accelerometertest/com.example.accelerometertest.MainActivity}: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.os.Looper.loop(Looper.java:137)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread.main(ActivityThread.java:5041)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at java.lang.reflect.Method.invokeNative(Native Method)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at java.lang.reflect.Method.invoke(Method.java:511)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at dalvik.system.NativeStart.main(Native Method)
06-26 20:49:43.640: E/AndroidRuntime(4138): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.view.ViewRootImpl.setView(ViewRootImpl.java:571)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:246)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.Dialog.show(Dialog.java:281)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at com.example.accelerometertest.MainActivity.onCreate(MainActivity.java:67)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.Activity.performCreate(Activity.java:5104)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-26 20:49:43.640: E/AndroidRuntime(4138):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
06-26 20:49:43.640: E/AndroidRuntime(4138):     ... 11 more

Answer 1

改变

 builder = new AlertDialog.Builder(this.getApplicationContext());

到（只要this是你的 MainActivity ）

 builder = new AlertDialog.Builder(this);