Why SwipeRefreshLayout dont work, when first model is hidden.

I use Epoxy to manage RecycleView inside SwipeRefreshLayout, like below:

 <android.support.v4.widget.SwipeRefreshLayout
      android:id="@+id/srLayout"
      android:layout_width="match_parent"
      android:layout_height="match_parent">

      <android.support.v7.widget.RecyclerView
          android:id="@+id/rvList"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/>
  </android.support.v4.widget.SwipeRefreshLayout>

It is weird when I hide first model of RecycleView by EpoxyModel.hide(), SwipeRefreshLayout doesn’t work anymore. I create a TestProject, https://github.com/fanxu123/EpoxyTest, specially for demonstration. Please help, thanks.

[SamThompson]

I was able to track the bug down to LinearLayoutManager.

Before showing the refresh spinner, SwipeRefreshLayout makes a check to whether or not RecyclerView can be scrolled in the negative direction:

        // from SwipeRefreshLayout#onNestedScroll
        final int dy = dyUnconsumed + mParentOffsetInWindow[1];
        if (dy < 0 && !canChildScrollUp()) {  // <-- evaluates to false and never shows the spinner 
                                              // b/c canChildScrollUp() == true
            mTotalUnconsumed += Math.abs(dy);
            moveSpinner(mTotalUnconsumed);
        }

the conditional dy < 0 && !canChildScrollUp() evaluates to false. Tracing canChildScrollUp(), it eventually leads us to this code in LinearLayoutManager:

    private int computeScrollOffset(RecyclerView.State state) {
        if (getChildCount() == 0) {
            return 0;
        }
        ensureLayoutState();
        return ScrollbarHelper.computeScrollOffset(state, mOrientationHelper,
                findFirstVisibleChildClosestToStart(!mSmoothScrollbarEnabled, true),
                findFirstVisibleChildClosestToEnd(!mSmoothScrollbarEnabled, true),
                this, mSmoothScrollbarEnabled, mShouldReverseLayout);
    }

The call to findFirstVisibleChildClosestToStart will return the first non-hidden item (since the height of a hidden item is 0dp and isn’t considered visible by the layout manager). However, because there is still technically an item before the first non-hidden item, the layout manager still considers the RecyclerView scrollable in the negative direction due to this math:

// final return in ScrollbarHelper#computeScrollOffset
return Math.round(itemsBefore * avgSizePerRow + (orientation.getStartAfterPadding()
                - orientation.getDecoratedStart(startChild)))

Let me know if that explanation is unclear and I can do my best to clarify. I can imagine a similar thing is happening in #61

[SiarheiSm]

workaround:

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.recyclerview.widget.RecyclerView
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </FrameLayout>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>