[ConditionalDivider] an recyclerview for LinearLayoutManager which support conditional drawing #divider #conditional #recyclerview #android

ConditionalDivider.kt

/**
 * ConditionalDivider is a [RecyclerView.ItemDecoration] that can be used as a divider
 * between items of a [LinearLayoutManager]. It supports both [.HORIZONTAL] and
 * [.VERTICAL] orientations.
 *
 * <pre>
 * dividerItemDecoration = new DividerItemDecoration(recyclerView.getContext(),
 * mLayoutManager.getOrientation());
 * recyclerView.addItemDecoration(dividerItemDecoration);
</pre> *
 */
class ConditionalDivider
/**
 * Creates a divider [RecyclerView.ItemDecoration] that can be used with a
 * [LinearLayoutManager].
 *
 * @param context Current context, it will be used to access resources.
 * @param orientation Divider orientation. Should be [.HORIZONTAL] or [.VERTICAL].
 */
    (context: Context, orientation: Int = LinearLayout.VERTICAL) : RecyclerView.ItemDecoration() {

    var conditionToShowDivider: ((itemPosition: Int) -> Boolean)? = null

    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) {
        if (orientation != HORIZONTAL && orientation != VERTICAL) {
            throw IllegalArgumentException(
                "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) {
        if (drawable == null) {
            throw IllegalArgumentException("Drawable cannot be null.")
        }
        mDivider = drawable
    }

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

        if (mOrientation == VERTICAL) {
            drawVertical(c, parent)
        } else {
            drawHorizontal(c, parent)
        }
    }

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

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

        val childCount = parent.childCount
        for (i in 0 until childCount) {
            if (conditionToShowDivider==null || conditionToShowDivider?.invoke(i)==true) {
                val child = parent.getChildAt(i)
                parent.getDecoratedBoundsWithMargins(child, mBounds)
                val bottom = mBounds.bottom + Math.round(child.translationY)
                val top = bottom - mDivider!!.intrinsicHeight
                mDivider?.setBounds(left, top, right, bottom)
                mDivider?.draw(canvas)
            }
        }
        canvas.restore()
    }

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

        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
        for (i in 0 until childCount) {
            if (conditionToShowDivider==null || conditionToShowDivider?.invoke(i)==true) {
                val child = parent.getChildAt(i)
                parent.layoutManager?.getDecoratedBoundsWithMargins(child, mBounds)
                val right = mBounds.right + Math.round(child.translationX)
                val left = right - mDivider!!.intrinsicWidth
                mDivider?.setBounds(left, top, right, bottom)
                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
        }
        if (mOrientation == VERTICAL) {
            outRect.set(0, 0, 0, mDivider!!.intrinsicHeight)
        } else {
            outRect.set(0, 0, mDivider!!.intrinsicWidth, 0)
        }
    }

    companion object {
        val HORIZONTAL = LinearLayout.HORIZONTAL
        val VERTICAL = LinearLayout.VERTICAL

        private val TAG = "DividerItem"
        private val ATTRS = intArrayOf(android.R.attr.listDivider)
    }
}