Android使用popUpWindow带遮罩层的弹出框

public class MainActivity extends Activity {
 private RelativeLayout layout;
 private Button btn;
 private boolean isFold=true; // 判断是否显示
 private PopupWindow taxWindow; // 弹出框
 private TextView tv=null; // 遮罩层
 
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    layout=(RelativeLayout)findViewById(R.id.layout);
    btn=(Button)findViewById(R.id.btn);
    btn.setOnClickListener(new View.OnClickListener(){
     @Override
     public void onClick(View v){
     if(isFold){
      isFold=false;
        showTaxDetail(v);
      tv=new TextView(MainActivity.this);
        tv.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,ViewGroup.LayoutParams.FILL_PARENT));
        tv.setBackgroundColor(Color.parseColor("#66000000"));
        tv.setClickable(true);
        tv.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
   isFold=true;
       taxWindow.dismiss();
       layout.removeView(tv);
   }
  });
        layout.addView(tv);
     }
     else{
      isFold=true;
      taxWindow.dismiss();
      layout.removeView(tv);
     }
     }
    });
  }
  
  private void showTaxDetail(View view){
   LayoutInflater inflater=LayoutInflater.from(this);
   // 加载弹出框的布局
   View contentView=inflater.inflate(R.layout.ewj_tax_detail, null);
   contentView.measure(0,0);
   taxWindow=new PopupWindow(contentView,contentView.getMeasuredWidth(),contentView.getMeasuredHeight(),true);
   //taxWindow.setBackgroundDrawable(getResources().getDrawable(R.drawable.ic_launcher));
   //taxWindow.setOutsideTouchable(true);
   taxWindow.setFocusable(false);
   int[] location = new int[2]; 
   // 得到按钮控件的坐标，便于定位弹出框位置
    btn.getLocationInWindow(location);
    int taxWindowWidth=taxWindow.getContentView().getMeasuredWidth();
    int screenWidth = getWindowManager().getDefaultDisplay().getWidth(); 
    taxWindow.showAtLocation(btn,Gravity.NO_GRAVITY,(screenWidth-taxWindowWidth)/2,location[1]+95);
  }
}

taxWindow.showAsDropDown(anchor, xOffset, yOffset);