1、首先将xml布局(layout)转化为bitmap

fun getViewBitmap(layoutId: Int): Bitmap? {
        val view = layoutInflater.inflate(layoutId, null)
        val me = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED)
        view.measure(me, me)
        view.layout(0, 0, view.measuredWidth, view.measuredHeight)
        view.buildDrawingCache()
        return view.drawingCache
    }

2、转为drawable后添加，需要注意，必须给drawable设置gravity，bounds跟密度，否则会影响显示效果，红色99就是添加的view，受这三个参数影响

val viewBitmap = getViewBitmap(R.layout.red_oo)
        val bitmapDrawable = BitmapDrawable(null, viewBitmap).apply {
            setGravity(Gravity.END)
            setBounds(0,0,200,100)
            viewBitmap?.run {
                setTargetDensity(viewBitmap.density)
            }
        }
        findViewById.overlay.add(bitmapDrawable)