I have followed this Stack Overflow post to create a recyclerview with viewpager behavior.
Works fine but I need to trigger the scroll to next item when user lift the finger of the screen. Right now only snap to next item when it's 50% visible.
UPDATE WITH SOLUTION
The Crysxd response was the key. To detect the snap direction I added this code at the top of the findTargetSnapPosition function:
if (velocityY < 0)
snapToPrevious = true
else
snapToNext = true
There's no way around a custom SnapHelper. Here is a class you can copy to your project.
class ControllableSnapHelper(val onSnapped: ((Int) -> Unit)? = null) : LinearSnapHelper() {
var snappedPosition = 0
private var snapToNext = false
private var snapToPrevious = false
var recyclerView: RecyclerView? = null
override fun attachToRecyclerView(recyclerView: RecyclerView?) {
super.attachToRecyclerView(recyclerView)
this.recyclerView = recyclerView
}
override fun findTargetSnapPosition(layoutManager: RecyclerView.LayoutManager, velocityX: Int, velocityY: Int): Int {
if (snapToNext) {
snapToNext = false
snappedPosition = Math.min(recyclerView?.adapter?.itemCount ?: 0, snappedPosition + 1)
} else if (snapToPrevious) {
snapToPrevious = false
snappedPosition = Math.max(0, snappedPosition - 1)
} else {
snappedPosition = super.findTargetSnapPosition(layoutManager, velocityX, velocityY)
}
onSnapped?.invoke(snappedPosition)
return snappedPosition
}
fun snapToNext() {
snapToNext = true
onFling(Int.MAX_VALUE, Int.MAX_VALUE)
}
fun snapToPrevious() {
snapToPrevious = true
onFling(Int.MAX_VALUE, Int.MAX_VALUE)
}
}
You can replace LinearSnapHelper with PagerSnapHelper as well. Simply call snapToNext() or snapToPrevious(). I also implemented a callback which is passed in the constructor.
We simply overwrite the findTargetSnapPosition(...) method. This method can return any position and the SnapHelper implementation will then compute the scroll animation to get there. The functions snapToNext() and snapToPrevious() simply set a boolean which tells us to snap to the next or previous view the next time findTargetSnapPosition(...) is called. It would also be very simple to add a snapTo(index: Int) function. After setting the boolean, we need to start the snap progress. To do so, we call onFling(...) which would be called when the user moved the RecyclerView. We need to pass in a value which exceeds the minimum velocity set by SnapHelper, so we just use Int.MAX_VALUE. As we never call super.findTargetSnapPosition(...), the actual velocity used by PagerSnapHelper doesn't matter.
