android弹出popupwindow时使下层页面变灰色

点击弹出popupwindow代码：

 findViewById(R.id.btn).setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View arg0) {
                 // TODO Auto-generated method stub
                 lp=getWindow().getAttributes();
                 lp.alpha=0.3f;
                 getWindow().setAttributes(lp);

                 sharepopup=new ShareSelectPopupWindow(MainActivity.this,shareitemonClick);
                 sharepopup.setOnDismissListener(touchoutsidedismiss);
                 sharepopup.showAtLocation(findViewById(R.id.shopdetailparent), Gravity.BOTTOM|Gravity.CENTER_HORIZONTAL, 0, 0);
             }
         });

点击外层消失的代码：

 public OnDismissListener touchoutsidedismiss=new OnDismissListener(){

         @Override
         public void onDismiss() {
             // TODO Auto-generated method stub
           lp.alpha=1.0f;
           getWindow().setAttributes(lp);

         }
     };