Android自定义PopWindow带动画向下弹出效果

package dmpte.mytest;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.widget.PopupWindow;
import android.widget.RelativeLayout;

public class PopWin extends PopupWindow {
 private Context mContext;
 private View view;


 public PopWin(final Context mContext, View.OnClickListener itemsOnClick, int flag) {
  this.mCOntext= mContext;
  this.view = LayoutInflater.from(mContext).inflate(R.layout.view_popwin, null);
  // 设置外部可点击
  this.setOutsideTouchable(true);
  /* 设置弹出窗口特征 */
  // 设置视图
  this.setContentView(this.view);
  // 设置弹出窗体的宽和高
  this.setHeight(RelativeLayout.LayoutParams.WRAP_CONTENT);//高
  this.setWidth(RelativeLayout.LayoutParams.MATCH_PARENT);//宽

  // 设置弹出窗体可点击
  this.setFocusable(true);

  // 设置弹出窗体显示时的动画，从底部向上弹出
  this.setAnimationStyle(R.style.take_photo_anim);
//  mMenuView添加OnTouchListener监听判断获取触屏位置如果在选择框外面则销毁弹出框
  this.view.setOnTouchListener(new View.OnTouchListener() {
   @Override
   public boolean onTouch(View v, MotionEvent event) {
    int height = view.findViewById(R.id.pop_layout).getHeight();
    int y = (int) event.getY();
    if (event.getAction() == MotionEvent.ACTION_DOWN) {
    //Y表示手指点击的位置，屏幕顶端为0，往下一次递增。height是popwin的高度。y > height就表示手指点在popwin的外面，然后关闭popwin
     if (y > height) {
      dismiss();
     }
    }
    return true;
   }

  });

 }

}

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//让背景变暗
 WindowManager.LayoutParams lp = getWindow().getAttributes();
    lp.alpha = 0.7f;
    getWindow().setAttributes(lp);
    //弹出窗体
    PopWin popWin_ = new PopWin(this, null, 0);
    popWin_.showAsDropDown(findViewById(R.id.relativeLayout));
    //监听popwin是否关闭，关闭的话让背景恢复
    popWin_.setOnDismissListener(new PopupWindow.OnDismissListener() {
     @Override
     public void onDismiss() {
      WindowManager.LayoutParams lp = getWindow().getAttributes();
      lp.alpha = 1f;
      getWindow().setAttributes(lp);
  }
});