android使用PopupWindow实现页面点击顶部弹出下拉菜单

public class MainActivity extends Activity implements OnClickListener { 
  private PopupWindow popupwindow; 
  private Button button; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    button = (Button) findViewById(R.id.button1); 
    button.setOnClickListener(this); 
  } 
  @Override 
  public void onClick(View v) { 
    switch (v.getId()) { 
    case R.id.button1: 
      if (popupwindow != null&&popupwindow.isShowing()) { 
        popupwindow.dismiss(); 
        return; 
      } else { 
        initmPopupWindowView(); 
        popupwindow.showAsDropDown(v, 0, 5); 
      } 
      break; 
    default: 
      break; 
    } 
  } 
  public void initmPopupWindowView() { 
    // // 获取自定义布局文件pop.xml的视图 
    View customView = getLayoutInflater().inflate(R.layout.popview_item, 
        null, false); 
    // 创建PopupWindow实例,200,150分别是宽度和高度 
    popupwindow = new PopupWindow(customView, 250, 280); 
    // 设置动画效果 [R.style.AnimationFade 是自己事先定义好的] 
    popupwindow.setAnimationStyle(R.style.AnimationFade); 
    // 自定义view添加触摸事件 
    customView.setOnTouchListener(new OnTouchListener() { 
      @Override 
      public boolean onTouch(View v, MotionEvent event) { 
        if (popupwindow != null && popupwindow.isShowing()) { 
          popupwindow.dismiss(); 
          popupwindow = null; 
        } 
        return false; 
      } 
    }); 
    /** 在这里可以实现自定义视图的功能 */ 
    Button btton2 = (Button) customView.findViewById(R.id.button2); 
    Button btton3 = (Button) customView.findViewById(R.id.button3); 
    Button btton4 = (Button) customView.findViewById(R.id.button4); 
    btton2.setOnClickListener(this); 
    btton3.setOnClickListener(this); 
    btton4.setOnClickListener(this); 
  } 
} 

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<&＃63;xml version="1.0" encoding="UTF-8"&＃63;>