popWindow位置适配

/**
 *
 * @param pw     popupWindow
 * @param anchor v
 * @param xoff   x轴偏移
 * @param yoff   y轴偏移
 */
public static void showAsDropDown(final PopupWindow pw, final View anchor, final int xoff, final int yoff) {
    if (Build.VERSION.SDK_INT >= 24) {
        Rect visibleFrame = new Rect();
        anchor.getGlobalVisibleRect(visibleFrame);
        int height = anchor.getResources().getDisplayMetrics().heightPixels -                 
            visibleFrame.bottom;
        pw.setHeight(height);
        pw.showAsDropDown(anchor, xoff, yoff);
    } else {
        pw.showAsDropDown(anchor, xoff, yoff);
    }
}