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);