diff --git a/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountingManager.java b/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountingManager.java index 7d89e34ebf7..e48192e8963 100644 --- a/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountingManager.java +++ b/ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/MountingManager.java @@ -244,18 +244,36 @@ public class MountingManager { ViewGroupManager viewGroupManager = getViewGroupManager(viewState); - if (viewGroupManager.getChildCount(parentView) <= index) { + try { + viewGroupManager.removeViewAt(parentView, index); + } catch (RuntimeException e) { + // Note: `getChildCount` may not always be accurate! + // We don't currently have a good explanation other than, in situations where you + // would empirically expect to see childCount > 0, the childCount is reported as 0. + // This is likely due to a ViewManager overriding getChildCount or some other methods + // in a way that is strictly incorrect, but potentially only visible here. + // The failure mode is actually that in `removeViewAt`, a NullPointerException is + // thrown when we try to perform an operation on a View that doesn't exist, and + // is therefore null. + // We try to add some extra diagnostics here, but we always try to remove the View + // from the hierarchy first because detecting by looking at childCount will not work. + // + // Note that the lesson here is that `getChildCount` is not /required/ to adhere to + // any invariants. If you add 9 children to a parent, the `getChildCount` of the parent + // may not be equal to 9. This apparently causes no issues with Android and is common + // enough that we shouldn't try to change this invariant, without a lot of thought. + int childCount = viewGroupManager.getChildCount(parentView); + throw new IllegalStateException( "Cannot remove child at index " + index + " from parent ViewGroup [" + parentView.getId() + "], only " - + parentView.getChildCount() - + " children in parent"); + + childCount + + " children in parent. Warning: childCount may be incorrect!", + e); } - - viewGroupManager.removeViewAt(parentView, index); } @UiThread