Android中常見android.view.WindowManager$BadTokenException錯誤

項目中有時會出現如下的問題：

new AlertDialog.Builder(activity).setTitle(getResources().getString(R.string.testspeed_prompt))
                            .setCancelable(false)
                            .setMessage( getResources().getString(R.string.testspeed_networknotgood))
                            .setPositiveButton( getResources().getString(R.string.testspeed_postive),
                                    new DialogInterface.OnClickListener() {

                                        @Override
                                        public void onClick(DialogInterface dialog,
                                                int which) {
                                            dialog.dismiss();
                                            networkStatus = NetWorkUtil
                                                    .getNetworkStatus(context);
                                            changeUIByNetworkType(networkStatus);
                                        }
                                    }).show();

在彈出對話框時意外閃退，錯誤日誌如下：

android.view.WindowManager$BadTokenException: Unable to add window -- token android.os.BinderProxy@41c1d6f0 is not valid; is your activity running?
	at android.view.ViewRootImpl.setView(ViewRootImpl.java:518)
	at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:301)
	at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:215)
	at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:140)
	at android.view.Window$LocalWindowManager.addView(Window.java:537)
	at android.app.Dialog.show(Dialog.java:278)
	at android.app.AlertDialog$Builder.show(AlertDialog.java:932)
	at com.quickbird.speedtest.gui.activity.TestSpeedActivity$MainHandler.handleMessage(TestSpeedActivity.java:351)
	at android.os.Handler.dispatchMessage(Handler.java:99)
	at android.os.Looper.loop(Looper.java:137)
	at android.app.ActivityThread.main(ActivityThread.java:4439)
	at java.lang.reflect.Method.invokeNative(Native Method)
	at java.lang.reflect.Method.invoke(Method.java:511)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:787)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554)
	at dalvik.system.NativeStart.main(Native Method)

分析日誌原因是 一個activity在運行時纔可以添加窗體，因此可以這樣：

 Activity activity = TestSpeedActivity.this;
                while (activity.getParent() != null) {
                    activity = activity.getParent();
                }
                try {
                    new AlertDialog.Builder(activity).setTitle(getResources().getString(R.string.testspeed_prompt))
                            .setCancelable(false)
                            .setMessage( getResources().getString(R.string.testspeed_networknotgood))
                            .setPositiveButton( getResources().getString(R.string.testspeed_postive),
                                    new DialogInterface.OnClickListener() {

                                        @Override
                                        public void onClick(DialogInterface dialog,
                                                int which) {
                                            dialog.dismiss();
                                        }
                                    }).show();
                } catch (Exception e) {
                    DebugUtil.e("AlertDialog  Exception:" + e.getMessage());
                }