Android RecyclerView 吸顶效果(二)

请先阅读​​Android RecyclerView 吸顶效果(一)​​,推荐参考第一篇文章的方案来实现,这里只是帖一下第二种方案的代码,简单的介绍一下ItemDecoration

实现效果:

ItemDecoration

太懒了,截个图,如有侵权,请告知,会进行删除!

主要代码

StickyItemDecoration

class StickyItemDecoration(val context: Context, val mList: MutableList<Bean> = mutableListOf()) :
    RecyclerView.ItemDecoration() {

    private var paint: Paint? = null
    private var textPaint: Paint = Paint()
    private var dividerHeight: Float = dp2Px(50).toFloat()

    init {
        paint = Paint()
        paint?.setColor(context.resources.getColor(R.color.colorAccent))
        paint?.style = Paint.Style.FILL

        textPaint?.setColor(context.resources.getColor(R.color.FF333333))
        textPaint?.style = Paint.Style.FILL
        textPaint?.textSize = sp2Px(14).toFloat()
    }

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)
        val position = parent.getChildAdapterPosition(view)
        if (isGroupFirst(position)) {
            outRect.top = dividerHeight.toInt()
        } else {
            outRect.top = 0
        }
    }

    override fun onDraw(canvas: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        super.onDraw(canvas, parent, state)
        val childCount = parent.childCount
        for (i in 0 until childCount) {
            val childView = parent.getChildAt(i)
            val childAdapterPos = parent.getChildAdapterPosition(childView)
            val groupName = getGroupName(childAdapterPos)
            val left = childView.paddingLeft
            val right = childView.paddingRight
            paint?.let {
                if (isGroupFirst(childAdapterPos)) {
                    val top = childView.top - dividerHeight
                    val bottom = childView.top.toFloat()
                    canvas.drawRect(left.toFloat(), top, (childView.width - right).toFloat(), bottom, it)
                    groupName ?: return
                    val baseLine = (top + bottom) / 2f - (textPaint.descent() + textPaint.ascent()) / 2f
                    canvas.drawText(groupName, left + dp2Px(10).toFloat(), baseLine, textPaint)
                }
            }
        }
    }

    override fun onDrawOver(canvas: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        super.onDrawOver(canvas, parent, state)
        val firstVisiblePos = (parent.layoutManager as LinearLayoutManager).findFirstVisibleItemPosition()
        // 这里必须获取itemView 不能通过parent.getChildAt的方式，原因是getChildAt的方式会出现top准确的情况
        val view = parent.findViewHolderForAdapterPosition(firstVisiblePos)?.itemView
        view ?: return
        val top = parent.paddingTop
        val left = parent.paddingLeft
        val right = parent.width - view.paddingRight
        paint?.let {
            if (isGroupFirst(firstVisiblePos)) {
                val bottom = Math.min(dividerHeight, view.bottom.toFloat())
                canvas.drawRect(left.toFloat(), top + view.top - dividerHeight, right.toFloat(), top + bottom, it)
                val baseLine = ((top + bottom) - (textPaint.ascent() + textPaint.descent())) / 2f
                canvas.drawText(getGroupName(firstVisiblePos)!!, left + dp2Px(10).toFloat(), baseLine, textPaint)
            } else {
                canvas.drawRect(left.toFloat(), top.toFloat(), right.toFloat(), top.toFloat() + dividerHeight, it)
                val baseLine = ((top + top + dividerHeight) - (textPaint.ascent() + textPaint.descent())) / 2f
                canvas.drawText(getGroupName(firstVisiblePos)!!, left + dp2Px(10).toFloat(), baseLine, textPaint)
            }
        }
    }

    private fun getGroupName(position: Int): String? {
        return mList[position].groupName
    }

    private fun isGroupFirst(position: Int): Boolean {
        return if (position == 0) {
            true
        } else {
            val lastGroupName = mList[position - 1].groupName
            val currentGroupName = mList[position].groupName
            lastGroupName != currentGroupName
        }
    }

    private fun dp2Px(dpValue: Int): Int {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dpValue.toFloat(), context.resources.displayMetrics).toInt()
    }

    private fun sp2Px(spValue: Int): Int {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, spValue.toFloat(), context.resources.displayMetrics).toInt()
    }
}

数据

class Bean(val text: String, val groupName: String)

Activity

class SimpleActivity : AppCompatActivity() {
    private val beanList = mutableListOf<Bean>()
    private var recyclerView: RecyclerView? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_sample_2)
        initData()
        initRecyclerView()
    }

    private fun initRecyclerView() {
        recyclerView = findViewById(R.id.recyclerView)
        recyclerView?.adapter = SampleAdapter2(beanList)
        recyclerView?.layoutManager = LinearLayoutManager(this)
        recyclerView?.layoutParams?.width = ViewGroup.LayoutParams.MATCH_PARENT
        recyclerView?.layoutParams?.height = ViewGroup.LayoutParams.WRAP_CONTENT
        recyclerView?.addItemDecoration(StickyItemDecoration(this, beanList))
    }

    private fun initData() {
        for (i in 0..5) {
            beanList.add(Bean("第一组 ${i + 1} 号", "第一组"))
        }
        for (i in 0..5) {
            beanList.add(Bean("第二组 ${i + 1} 号", "第二组"))
        }
        for (i in 0..5) {
            beanList.add(Bean("第三组 ${i + 1} 号", "第三组"))
        }
        for (i in 0..5) {
            beanList.add(Bean("第四组 ${i + 1} 号", "第四组"))
        }
        for (i in 0..5) {
            beanList.add(Bean("第五组 ${i + 1} 号", "第五组"))
        }
    }
}

Adapter

class SampleAdapter2(var data: MutableList<Bean>? = mutableListOf()) : RecyclerView.Adapter<Holder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): Holder {
        return Holder(LayoutInflater.from(parent.context).inflate(R.layout.item, parent, false))
    }

    override fun getItemCount(): Int {
        return data?.size ?: 0
    }

    override fun onBindViewHolder(holder: Holder, position: Int) {
        holder.bindData(data?.get(position)?.text)
    }
}

class Holder(view: View) : RecyclerView.ViewHolder(view) {
    private var textView: TextView? = null

    init {
        textView = view.findViewById(R.id.tv)
    }

    fun bindData(s: String?) {
        s ?: return
        textView?.text = s
    }
}