Android仿微信、qq点击右上角加号弹出操作框

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto">
  <item
    android:id="@+id/btn_msg"
    android:icon="@drawable/ic_notifications_none"
    android:title="消息"
    app:showAsAction="ifRoom" />
</menu>

@Override
  public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_index_msg, menu);
    return super.onCreateOptionsMenu(menu);

  }

@Override
  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
      case R.id.btn_msg:
        View popupView = IndexActivity.this.getLayoutInflater().inflate(R.layout.popupwindow, null);
        final PopupWindow window = new PopupWindow(popupView, 300, 220);
        ListView lv_msg = (ListView) popupView.findViewById(R.id.lv_msg);
        MsgAdapter msgAdapter = new MsgAdapter(context, msgBeans);
        lv_msg.setAdapter(msgAdapter);
        lv_msg.setOnItemClickListener(new AdapterView.OnItemClickListener() {
          @Override
          public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            if (window.isShowing()) {
              window.dismiss();
            }
            switch (position) {
              case 0:
                if (myApplication.isOnline()) {
                  NoticeMainActivity.startActivity(IndexActivity.this);
                } else {
                  Toast.makeText(IndexActivity.this, "离线状态不能使用此功能", Toast.LENGTH_SHORT).show();
                }
                break;
              case 1:
                if (myApplication.isOnline()) {
                  TaskMainActivity.startActivity(IndexActivity.this);
                } else {
                  Toast.makeText(IndexActivity.this, "离线状态不能使用此功能", Toast.LENGTH_SHORT).show();
                }
                break;
              default:
                break;
            }
          }
        });
        window.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#F8F8F8")));
        window.setFocusable(true);
        window.setOutsideTouchable(true);

        window.update();

        //设置显示位置

        window.showAsDropDown(msgView, 0, 0);//msgView就是我们menu中的btn_msg
        break;
      default:
        break;
    }
    return super.onOptionsItemSelected(item);
  }

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical">
  <ListView
    android:id="@+id/lv_msg"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:divider="@null"
    android:scrollbars="none" />
</LinearLayout>