recyclerView grid 模式的分割线绘制

GridItemDecoration.kt

private class StaggeredGridItemDecoration(
    context: Context,
    orientation: Int,
    private val spanCount: Int
) : RecyclerView.ItemDecoration() {
    companion object {
        const val HORIZONTAL = LinearLayout.HORIZONTAL
        const val VERTICAL = LinearLayout.VERTICAL
        const val STAGGEREDGRID = 31
        private val TAG = "DividerItem"
        private val ATTRS = intArrayOf(android.R.attr.listDivider)
    }

    private var mDivider: Drawable? = null

    /**
     * Current orientation. Either [.HORIZONTAL] or [.VERTICAL].
     */
    private var mOrientation: Int = 0

    private val mBounds = Rect()

    init {
        val a = context.obtainStyledAttributes(ATTRS)
        mDivider = a.getDrawable(0)
        if (mDivider == null) {
            Log.w(
                TAG,
                "@android:attr/listDivider was not set in the theme used for this "
                        + "DividerItemDecoration. Please set that attribute all call setDrawable()"
            )
        }
        a.recycle()
        setOrientation(orientation)
    }

    /**
     * Sets the orientation for this divider. This should be called if
     * [RecyclerView.LayoutManager] changes orientation.
     *
     * @param orientation [.HORIZONTAL] or [.VERTICAL]
     */
    fun setOrientation(orientation: Int) {
        require(
            !(orientation != HORIZONTAL
                    && orientation != VERTICAL
                    && orientation != STAGGEREDGRID)
        ) { "Invalid orientation. It should be either HORIZONTAL or VERTICAL" }
        mOrientation = orientation
    }

    /**
     * Sets the [Drawable] for this divider.
     *
     * @param drawable Drawable that should be used as a divider.
     */
    fun setDrawable(drawable: Drawable) {
        mDivider = drawable
    }

    /**
     * @return the [Drawable] for this divider.
     */
    fun getDrawable(): Drawable? {
        return mDivider
    }

    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        if (parent.layoutManager == null || mDivider == null) {
            return
        }
        when (mOrientation) {

            VERTICAL -> {
                drawVertical(c, parent)
            }
            HORIZONTAL -> {
                drawHorizontal(c, parent)
            }
            STAGGEREDGRID -> {
                drawMulti(c, parent)
            }

        }
    }

    private fun drawMulti(canvas: Canvas, parent: RecyclerView) {
        drawVertical(canvas, parent)
        drawHorizontal(canvas, parent)
    }

    private fun drawVertical(canvas: Canvas, parent: RecyclerView) {
        canvas.save()
        var left: Int
        val right: Int

        var itemRight = 0

        if (parent.clipToPadding) {
            left = parent.paddingLeft
            right = parent.width - parent.paddingRight
            canvas.clipRect(
                left, parent.paddingTop, right,
                parent.height - parent.paddingBottom
            )
        } else {
            @Suppress("UNUSED_VALUE")
            left = 0
            right = parent.width
        }

        val childCount = parent.childCount
        LogUtils.e("child count = $childCount")
        for (i in 0 until childCount) {
            var count = ((i + 1) % spanCount)
            count = if (count == 0) spanCount else count
            // LogUtils.w("$i , $count")
            itemRight = count * right / spanCount
            left = (count - 1) * right / spanCount
            val child = parent.getChildAt(i)
            parent.getDecoratedBoundsWithMargins(child, mBounds)
            val bottom = mBounds.bottom + child.translationY.roundToInt()
            val top = bottom - mDivider!!.intrinsicHeight
            mDivider!!.setBounds(left, top, itemRight, bottom)
            mDivider!!.draw(canvas)
        }
        canvas.restore()
    }

    private fun drawHorizontal(canvas: Canvas, parent: RecyclerView) {
        canvas.save()
        var top: Int
        val bottom: Int

        var itemHeight = 0
        if (parent.clipToPadding) {
            top = parent.paddingTop
            bottom = parent.height - parent.paddingBottom
            canvas.clipRect(
                parent.paddingLeft, top,
                parent.width - parent.paddingRight, bottom
            )
        } else {
            top = 0
            bottom = parent.height
        }

        val childCount = parent.childCount
        LogUtils.e("child count = $childCount")

        var line = 0
        val totalLine = childCount / spanCount + if (childCount % spanCount > 0) 1 else 0
        for (i in 0 until childCount) {
            if ((i + 1) % (spanCount) == 1) {
                line += 1
            }
            itemHeight = bottom * line / totalLine
            top = bottom * (line - 1) / totalLine
            LogUtils.w("$i , $line , $itemHeight")
            val child = parent.getChildAt(i)
            parent.layoutManager!!.getDecoratedBoundsWithMargins(child, mBounds)
            val right = mBounds.right + child.translationX.roundToInt()
            val left = right - mDivider!!.intrinsicWidth
            mDivider!!.setBounds(left, top, right, itemHeight)
            mDivider!!.draw(canvas)
        }
        canvas.restore()
    }

    override fun getItemOffsets(
        outRect: Rect, view: View, parent: RecyclerView,
        state: RecyclerView.State
    ) {
        if (mDivider == null) {
            outRect.set(0, 0, 0, 0)
            return
        }
        when (mOrientation) {
            VERTICAL -> {
                outRect.set(0, 0, 0, mDivider!!.intrinsicHeight)
            }
            HORIZONTAL -> {
                outRect.set(0, 0, mDivider!!.intrinsicWidth, 0)
            }
            STAGGEREDGRID -> {
                outRect.set(0, 0, mDivider!!.intrinsicWidth, mDivider!!.intrinsicHeight)
            }
        }
    }
}

调用也很简单，就是要加一个 spanCount:Int 参数。

recyclerView.addItemDecoration(
            StaggeredGridItemDecoration(
                this,
                StaggeredGridItemDecoration.STAGGEREDGRID,
                4
            )
        )