Default effect
Expected effect
Dash line is GridLayoutManger default each item's left
How to implement？You need know blew point.
- Dash line is spanIndex*spanWidth
- item.left= Dash line location+ItemDecoration.left
So through set itemDecoration.left ,we could implement the average effect.
The Code
private class AverageGridItemDecoration : RecyclerView.ItemDecoration() {
override fun getItemOffsets(
outRect: Rect,
view: View,
parent: RecyclerView,
state: RecyclerView.State
) {
super.getItemOffsets(outRect, view, parent, state)
val layoutManager = parent.layoutManager as? GridLayoutManager ?: return
val spanCount = layoutManager.spanCount
val parentWidth = parent.measuredWidth - parent.paddingStart - parent.paddingEnd
val itemWidth = view.resources.getDimension(R.dimen.course_practice_result_item_size)
val spanWidth = parentWidth / spanCount
if (spanCount == 1) return
val spanMargin = (parentWidth - itemWidth * spanCount) / (spanCount - 1)
val spanSizeLookup = layoutManager.spanSizeLookup
for (child in parent) {
val adapterPosition = parent.getChildAdapterPosition(child)
val columnIndex = spanSizeLookup.getSpanIndex(adapterPosition, spanCount)
// Core line:
// left = expect left- default left
outRect.left = ((itemWidth + spanMargin) * columnIndex - spanWidth * columnIndex).toInt()
if (spanSizeLookup.getSpanGroupIndex(adapterPosition, spanCount) > 0) {
outRect.top = dp2px(15f).toInt()
}
}
}
}