android PopupWindow无法从自定义操作栏打开

Question

NewChatThroughNotification extends BaseActivity
    super.onCreate(savedInstanceState);
    /* setContentView(R.layout.notification_chat); */
    setContentView(R.layout.activitychat);
    setUpActionBar();

private void setUpActionBar() {
        ActionBar mActionBar = getSupportActionBar();
        mActionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
        mActionBar.setCustomView(R.layout.chat_custom_actionbar);
        mActionBar.getCustomView().findViewById(R.id.headerLayout)
                .setOnClickListener(this);
        mActionBar.getCustomView().findViewById(R.id.imgAttachment)
                .setOnClickListener(this);
    }


case R.id.imgAttachment:
            System.out.println( "!!!!attachment called....");
            showChatMenuDialog();

private void showChatMenuDialog() {
        System.out.println("MENU CALLED");
        LayoutInflater layoutInflater = (LayoutInflater) getBaseContext()
                .getSystemService(LAYOUT_INFLATER_SERVICE);
        View popupView = layoutInflater.inflate(
                R.layout.attachment_popup, null);
        final PopupWindow popupWindow = new PopupWindow(popupView,
                LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        popupWindow.showAsDropDown(imgAttachment, 30, 30);

Logcat：

1-11 16:40:59.936: W/dalvikvm(24579): threadid=1: calling UncaughtExceptionHandler
11-11 16:40:59.937: E/AndroidRuntime(24579): FATAL EXCEPTION: main
11-11 16:40:59.937: E/AndroidRuntime(24579): Process: com.addonwebsolution.yarg, PID: 24579
11-11 16:40:59.937: E/AndroidRuntime(24579): java.lang.NullPointerException
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.widget.PopupWindow.registerForScrollChanged(PopupWindow.java:1663)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:958)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:933)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at com.addonwebsolution.yarg.NewChatThroughNotification.showChatMenuDialog(NewChatThroughNotification.java:147)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at com.addonwebsolution.yarg.NewChatThroughNotification.onClick(NewChatThroughNotification.java:81)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.view.View.performClick(View.java:4562)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.view.View$PerformClick.run(View.java:18918)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.os.Handler.handleCallback(Handler.java:808)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.os.Handler.dispatchMessage(Handler.java:103)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.os.Looper.loop(Looper.java:193)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at android.app.ActivityThread.main(ActivityThread.java:5388)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at java.lang.reflect.Method.invokeNative(Native Method)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at java.lang.reflect.Method.invoke(Method.java:515)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:655)
11-11 16:40:59.937: E/AndroidRuntime(24579):    at dalvik.system.NativeStart.main(Native Method)