flexbox-layout
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Scroll view sluggish and jittery
- [x] I have searched existing issues and confirmed this is not a duplicate
Issues and steps to reproduce
I use FlexboxLayoutManager with RecyclerView.Adapter to show short texts of roughly 4x20 on the screen at any time. To isolate the issue from data loading, I tested with a static set of items about 1000 loaded. As I scroll down, new items are shown from below and older items go out from the top. When I scroll fast, the views become very sluggish and jittery with abrupt stops in between. Interestingly, the sluggishness only seems to happen when I scroll down (scrolling up appears much better), even scrolling down again after having scrolled back up.
I have a RecyclerView within a LinearLayout, as
<LinearLayout
android:id="@+id/activity_words"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/words_list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="start"
android:scrollbars="vertical"
android:verticalSpacing="10dp" >
</androidx.recyclerview.widget.RecyclerView>
</LinearLayout>
Each item for the RecyclerView is defined as:
<LinearLayout
android:id="@+id/lauout"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="@dimen/list_padding">
<TextView
android:id="@+id/term"
android:text="@{word.term}"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="start"
android:textSize="@dimen/title_size"
android:minWidth="50dp"
android:paddingLeft="5dp"
android:paddingRight="5dp"
android:textStyle="normal|bold"/>
</LinearLayout>
In Java code,
FlexboxLayoutManager layoutManager = new FlexboxLayoutManager(this);
layoutManager.setFlexDirection(FlexDirection.ROW);
layoutManager.setJustifyContent(JustifyContent.FLEX_START);
layoutManager.setItemPrefetchEnabled(true);
binding.wordsList.setLayoutManager(layoutManager);
adapter.setTermSize(25f);
binding.wordsList.setAdapter(adapter);
Expected behavior
I expect to see smoother scrolling
As I browsed through the code, without fully comprehending it, I found something I can't explain. In FlexboxLayoutManager.java, view cache is cleared while scrolling:
@Override
public int scrollVerticallyBy(int dy, RecyclerView.Recycler recycler,
RecyclerView.State state) {
if (isMainAxisDirectionHorizontal() ||
(mFlexWrap == FlexWrap.NOWRAP && !isMainAxisDirectionHorizontal())) {
int scrolled = handleScrollingMainOrientation(dy, recycler, state);
mViewCache.clear();
return scrolled;
} else {
int scrolled = handleScrollingSubOrientation(dy);
mAnchorInfo.mPerpendicularCoordinate += scrolled;
mSubOrientationHelper.offsetChildren(-scrolled);
return scrolled;
}
}
I commented out the line mViewCache.clear();
in my local copy, then things appear drastically improved for me, at least scrolling down again becomes very smooth, though I don't know yet if it would cause other problems.
Version of the flexbox library
3.0.0