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canScrollHorizontally() crashes if the RecyclerView is not attached to the Window

See original GitHub issue

We have this use case where we might call recyclerView.smoothScrollToPosition on a view that has been removed from its container. In that case, we get the following crash:

        Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getWidth()' on a null object reference
        at com.google.android.flexbox.FlexboxLayoutManager.canScrollHorizontally(FlexboxLayoutManager.java:1900)
        at com.google.android.flexbox.FlexboxLayoutManager.getChildWidthMeasureSpec(FlexboxLayoutManager.java:483)
        at com.google.android.flexbox.FlexboxHelper.calculateFlexLines(FlexboxHelper.java:458)
        at com.google.android.flexbox.FlexboxHelper.calculateHorizontalFlexLines(FlexboxHelper.java:243)
        at com.google.android.flexbox.FlexboxLayoutManager.updateFlexLines(FlexboxLayoutManager.java:955)
        at com.google.android.flexbox.FlexboxLayoutManager.onLayoutChildren(FlexboxLayoutManager.java:731)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3924)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3641)
        at androidx.recyclerview.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1858)
        at androidx.recyclerview.widget.RecyclerView$ViewFlinger.run(RecyclerView.java:5044)

Sample code to reproduce the issue => https://github.com/martinbonnin/FlexboxTest. It mainly boils down to:

        val recyclerView = RecyclerView(this)
        recyclerView.layoutManager =  FlexboxLayoutManager(this)
        recyclerView.adapter = object: RecyclerView.Adapter<RecyclerView.ViewHolder>() {
            [....]
        }
        recyclerView.smoothScrollToPosition(500)

I understand scrolling on a non-visible View is not the most useful thing to do but I would still expect the LayoutManager to handle this case gracefully ?

Issue Analytics

State:
Created 5 years ago
Reactions:1
Comments:6 (2 by maintainers)

Top GitHub Comments

2reactions

KryptKodecommented, Apr 19, 2019

A workaround is to clone the library and perform a check on line 1901 @Override public boolean canScrollHorizontally() { if (mFlexWrap == FlexWrap.NOWRAP) { return isMainAxisDirectionHorizontal(); } else { return !isMainAxisDirectionHorizontal() || getWidth() > (mParent != null ? mParent.getWidth() : 0); } } I created a PR for the fix here

0reactions

martinbonnincommented, Feb 14, 2019

@bgorkowy I workaround’d the issue for now

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