Android 7.0+ popwindow的适配

 override fun showAsDropDown(anchor: View?) {
        if (Build.VERSION.SDK_INT >= 24) {
            val rect = Rect()
            anchor!!.getWindowVisibleDisplayFrame(rect)
            val h = anchor.resources.displayMetrics.heightPixels - rect.bottom
            height = h
        }
        super.showAsDropDown(anchor)
    }