android CoordinatorLayout滑动标题背景渐

监听事件

barLay.addOnOffsetChangedListener(this)

override fun onOffsetChanged(appBarLayout: AppBarLayout?, verticalOffset: Int) {
        Log.e("height", verticalOffset.toString())
        val verticalHeight = abs(verticalOffset)
        val collHeight = rlCollLay.height
        if (verticalHeight >= collHeight - 5 ){
            tvAcTitle.text = "个人主页"
        }else{
            tvAcTitle.text = ""
        }
        //这个就是关键方法了，大家可根据实际需要进行编写
        if (verticalOffset < 0){
            when (verticalHeight) {
                in 0..10 -> {//最好多写一点儿，避免出现问题
                    coordLay.setBackgroundColor(ContextCompat.getColor(this,R.color.transparent))
                }
                in 1..collHeight -> {
                    val scale: Float = verticalOffset.toFloat() / collHeight
                    val alpha = 255 * (1 - scale)
                    coordLay.setBackgroundColor(Color.argb(alpha.toInt(), 255, 255, 255))
                }
                else ->{
                    coordLay.setBackgroundColor(ContextCompat.getColor(this,R.color.transparent))
                }
            }
        }
       //追加一个判断，避免存在一点儿朦层效果
       if (verticalHeight in 0..10){
            coordLay.setBackgroundColor(ContextCompat.getColor(this,R.color.transparent))
        }
    }