问题 Android PopupWindow可以显示另一个PopupWindow吗？

Android PopupWindow可以显示另一个PopupWindow吗？ 可以在同一时间打开多少PopupWindow？只有一个？

第一个PopupWindow正常显示。但是在按钮点击（在第一个PopupWindow内容视图中）我有一个例外：

08-13 16:28:38.682: ERROR/AndroidRuntime(11760): FATAL EXCEPTION: main
        android.view.WindowManager$BadTokenException: Unable to add window -- token android.view.ViewRootImpl$W@41286250 is not valid; is your activity running?
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:600)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:313)
        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.widget.PopupWindow.invokePopup(PopupWindow.java:992)
        at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:901)
        at org.example.qberticus.quickactions.BetterPopupWindow.showLikePopDownMenu(BetterPopupWindow.java:159)
        at org.example.qberticus.quickactions.BetterPopupWindow.showLikePopDownMenu(BetterPopupWindow.java:129)
        at name.antonsmirnov.android.popup.ui.MainActivity$1$1.run(MainActivity.java:44)
        at android.app.Activity.runOnUiThread(Activity.java:4170)
        at name.antonsmirnov.android.popup.ui.MainActivity$1.onClick(MainActivity.java:42)
        at android.view.View.performClick(View.java:3558)
        at android.view.View$PerformClick.run(View.java:14157)
        at android.os.Handler.handleCallback(Handler.java:605)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4514)
        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:790)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
        at dalvik.system.NativeStart.main(Native Method)

代码是：

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);
    bindControls();
    initControls();
}

private Button button;

private void bindControls() {
    button = (Button) findViewById(R.id.button);
}

private void initControls() {
    initButton(button);
}

private void initButton(final Button button) {
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            final BetterPopupWindow window = new BetterPopupWindow(button);

            View popupview = createPopupView();
            window.setContentView(popupview);
            runOnUiThread(new Runnable() {
                public void run() {
                    window.showLikePopDownMenu();
                }
            });
        }
    });
}

private View createPopupView() {
    View v = LayoutInflater.from(MainActivity.this).inflate(R.layout.window, null);
    Button popupButton = (Button) v.findViewById(R.id.popupbutton);
    initButton(popupButton);
    return v;
}