I have a FragmentStateAdapter that is attached to new ViewPager2. In the previous ViewPager implementation there were number of ways to implement endless/infinite scroll. How to do so in ViewPager2?
Thanks in advance.
I have a FragmentStateAdapter that is attached to new ViewPager2. In the previous ViewPager implementation there were number of ways to implement endless/infinite scroll. How to do so in ViewPager2?
Thanks in advance.
This is what I came up with:
class EndlessScrollAdapter internal constructor(
fm: FragmentManager,
lifeCycle: Lifecycle
) : FragmentStateAdapter(fm, lifeCycle) {
private val items = mutableListOf<YourModel>()
val firstElementPosition = Int.MAX_VALUE / 2
fun updateList(list: List<YourModel>) {
items.apply {
clear()
addAll(list)
}
notifyDataSetChanged()
}
override fun getItemCount(): Int = if (items.isNotEmpty()) Int.MAX_VALUE else 0
override fun createFragment(position: Int): Fragment = YourPagerFragment(
items[position.rem(items.size)])
}
In Activity or Fragment we need to call:
viewPager2.adapter = endlessScrollAdapter
endlessScrollAdapter.apply {
updateList(yourModelList)
viewPager2.setCurrentItem(this.firstElementPosition, false)
}
Literally it's not endless but from the user perspective it is, as he will never reach to the edge. The lenght of ViewPager2 is Int.MAX_VALUE
, the start position is Int.MAX_VALUE/2
so user can scroll foward and backwards.
I am quite new to android and I passed the whole day reading all posts I could find about this problem. I also have a FragmentStateAdapter with 3 Fragments attached to a viewPager2.
My solution was to override the OnPageChangeCallback
event. Here, I saved in 2 local variables the state and the currentPosition; then, in the onPageScrolled
, I added a control to understand:
If all these conditions were true and I was on the first page, then I would set the next page to be the last and vice versa.
Here is my code. I used 0 and 2 because I have 3 Fragments.
viewPager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback()
{
private int myState;
private int currentPosition;
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
{
if (myState == ViewPager2.SCROLL_STATE_DRAGGING && currentPosition == position && currentPosition == 0)
viewPager2.setCurrentItem(2);
else if (myState == ViewPager2.SCROLL_STATE_DRAGGING && currentPosition == position && currentPosition == 2)
viewPager2.setCurrentItem(0);
super.onPageScrolled(position, positionOffset, positionOffsetPixels);
}
@Override
public void onPageSelected(int position)
{
currentPosition = position;
super.onPageSelected(position);
}
@Override
public void onPageScrollStateChanged(int state)
{
myState = state;
super.onPageScrollStateChanged(state);
}
});
you should return first or last position of view_pager when scrolling finished.
see this issue - Changing ViewPager to enable infinite page scrolling
Define a class extending ViewPager2.OnPageChangeCallback :
class ViewPager2PageChangeCallback(private val listener: (Int) -> Unit) :
ViewPager2.OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
super.onPageSelected(position)
when (position) {
0 -> listener.invoke(5). // 0th element is a fake element in your list. When 0th element is opened(from 1 to 0) automatically open last element(5th index)
6 -> listener.invoke(1). // 6th element is a fake element in your list. When 6th element is opened(from 5 to 6) automatically open first element(1th index)
}
}
}
Then create an instance from it in your activity.
onCreate(){
viewPager2PageChangeCallback = ViewPager2PageChangeCallback {
viewPager2.post {
viewPager2.setCurrentItem(it, false)
}
}
viewPager2.registerOnPageChangeCallback(viewPager2PageChangeCallback)
}
Unregister from it when activity is destroyed.
override fun onDestroy() {
super.onDestroy()
viewPager2.unregisterOnPageChangeCallback(viewPager2PageChangeCallback)
}