title: can't show alert dialog
body: <p>I can't show alert dialog. Everything is right until I set the method dialog.show(), then I can't open my application. Without this method everything is fine.</p>
  
  <p>I declared two global objects:</p>
  
  <pre><code>AlertDialog.Builder builder;
  AlertDialog dialog;
  </code></pre>
  
  <p>Then in MainActivity, I build a dialog by builder and create it.</p>
  
  <pre><code>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();
  </code></pre>
  
  <p>To this moment everything works and there's no any exceptions, but when I want to show the dialog, some exceptions appear and I can't run this application:</p>
  
  <pre><code>dialog.show();  //this method doesn't work and causes problems
  </code></pre>
  
  <p>What did I do wrong?</p>
  
  <p>EDIT:
  Exceptions:</p>
  
  <pre><code>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 &lt;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 &lt;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
  </code></pre>