private void popupWindows(List<String> list){
  //产生背景变暗效果
  WindowManager.LayoutParams lp=getWindow().getAttributes();
  lp.alpha = 0.4f;
  getWindow().setAttributes(lp);

    ......省略号......

  mPopupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {
      @Override
      public void onDismiss() {
        WindowManager.LayoutParams lp = getWindow().getAttributes();
        lp.alpha = 1f;
        getWindow().setAttributes(lp);
      }
    });

   ......省略号......

}

<!-- popup蒙板 -->
<LinearLayout
  android:id="@+id/ll_popup_hide"
  android:layout_width="match_parent"
  android:background="@color/hide_bg"
  android:orientation="vertical"
  android:layout_height="match_parent">
</LinearLayout>

<color name="hide_bg">#88323232</color>

ll_popup_hide.setVisibility(View.VISIBLE); //显示蒙板
ll_popup_hide.setVisibility(View.INVISIBLE); //隐藏蒙板