Too late for an answer, but maybe this will help someone.
I struggled with the same issue and couldn't find an acceptable solution.
Solved by following:
- First, you need to override onMeasure from the RecyclerView to save the largest element height:
class CustomRecycleView(ctx: Context, attrs: AttributeSet) : RecyclerView(ctx, attrs) {
private var biggestHeight: Int = 0
override fun onMeasure(widthSpec: Int, heightSpec: Int) {
for (i in 0 until childCount) {
val child = getChildAt(i)
child.measure(widthSpec, MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED))
val h = child.measuredHeight
if (h > biggestHeight) biggestHeight = h
}
super.onMeasure(widthSpec, MeasureSpec.makeMeasureSpec(biggestHeight, MeasureSpec.EXACTLY))
}
}
In you layout replace RecycleView with this CustomRecycleView:
onMeasure is called when a new element in the list is visible, and if the element is the highest, then we save this value. For example: if the first element has lowest height but lates has highest then at start RecycleView will be have height match to first element but after scrolling it will stay match to highest.
If you don't need to make RecycleView height match to highest item at start then you can stop here.
- To do this at the beginning, you must make a hack (based on @MidasLefko suggestion):
To find out initially what the height of the highest element will be, you need to add a scroll mechanism to the end and the beginning. I did it as follows:
private fun initRecycleView(items: ArrayList<Object>) {
val adapter = Adapter()
rv.visibility = View.INVISIBLE
rv.vadapter = adapter
rv.layoutManager = LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false)
rv.setHasFixedSize(true)
rv.smoothScrollToPosition(pinnedPosts.size)
Handler().postDelayed({
rv.smoothScrollToPosition(0)
}, 300)
Handler().postDelayed({
rv.visibility = View.VISIBLE
}, 700)
}
Set the visibility of Recycle view to INVISIBLE and after 700 milliseconds to VISIBLE to make this process invisible for user. Also, scrolling to start is performed with a delay of 300 milliseconds, because without some delay it can work incorrectly. In my case, this is needed for a list of 3 elements, and these delays is optimal for me.
Also remember to remove all Handler callbacks in onStop ()
The gray area is visible viewport.