请教 为什么不能弹出 popupwindow

请问 为什么不能弹出 popupwindow
请问 如下代码，当点击imageview_popwindow 按钮的时候 ，为什么没有在imageview_popwindow 下方出现popupwindow呢？（也就是点击后，没有反应）
 麻烦会的朋友帮忙回复下，谢谢啦

public class TestActivity extends Activity {
。。。
private PopupWindow mPopupWindow;
 private ImageView imageview_popwindow;

 protected void onCreate(Bundle savedInstanceState) {
   
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_first);

   //imageview_popwindow 按钮
  
  imageview_popwindow = (ImageView) findViewById(R.id.imageview_popwindow);

    imageview_popwindow.setOnClickListener( new OnClickListener() {
       public void onClick(View v){
       Log.d(TAG,"yong+oncreate:imageview_popwindow onClick() ");
       getPopupWindowInstance();
       mPopupWindow.showAsDropDown(imageview_popwindow );  //  想在imageview_popwindow   下方弹出 popupwindow
    }
   });
   
    }
    
    private void getPopupWindowInstance() {
      if( mPopupWindow != null) {
        mPopupWindow.dismiss();
     } else {
       initPopupWindow();
    }
 }

 private void initPopupWindow() {
     LayoutInflater layoutInflater = LayoutInflater.from(this);
     View popupWindow = layoutInflater.inflate(R.layout.popup_window, null);   // 布局文件  popup_window.xml 里边有个textview
     mPopupWindow = new PopupWindow(popupWindow,100,130);
   }
------解决思路----------------------
可以弹出来啊

Activity

package app.example.t;

import android.os.Bundle;
import android.app.Activity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.widget.PopupWindow;

public class MainActivity extends Activity {

	private PopupWindow mPopupWindow;
	private ImageView imageview_popwindow;

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		// imageview_popwindow 按钮

		imageview_popwindow = (ImageView) findViewById(R.id.imageview_popwindow);

		imageview_popwindow.setOnClickListener(new OnClickListener() {
			public void onClick(View v) {
				getPopupWindowInstance();
				mPopupWindow.showAsDropDown(imageview_popwindow); // 想在imageview_popwindow
																	// 下方弹出
																	// popupwindow
			}
		});

	}

	private void getPopupWindowInstance() {
		if (mPopupWindow != null) {
			mPopupWindow.dismiss();
		} else {
			initPopupWindow();
		}
	}

	private void initPopupWindow() {
		LayoutInflater layoutInflater = LayoutInflater.from(this);
		View popupWindow = layoutInflater.inflate(R.layout.popup_window, null); // 布局文件
																				// popup_window.xml
																				// 里边有个textview
		mPopupWindow = new PopupWindow(popupWindow, 100, 130);
	}
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ImageView
        android:id="@+id/imageview_popwindow"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:background="#ff33cc" />

</RelativeLayout>

popup_window.xml

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:text="一本正经" >

</TextView>

------解决思路----------------------
点击ImageView前



点击ImageView后



------解决思路----------------------
pwMyPopWindow.setBackgroundDrawable(this.getResources().getDrawable(
R.drawable.patientgroup_selected));// 设置背景图片，不能在布局中设置，要通过代码来设置

设置一下pwMyPopWindow的背景图片，我以前也遇到过，测试好多遍，才测试出给他设置背景图片就可以弹出来了，你试试吧我估计你就是这个问题