android彈出popupwindow時使下層頁面變灰色

點擊彈出popupwindow代碼：

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);
            }
        });

點擊外層消失的代碼：

public OnDismissListener touchoutsidedismiss=new OnDismissListener(){

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

        }
    };