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Fix double detach of kept-alive children in RenderTwoDimensionalViewport - #194917
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A kept-alive child lives in both `_children` and `_keepAliveBucket`, so `attach` and `detach` visited it twice and tripped the `_owner != null` assertion (e.g. a TableView inside a ListView with a selected cell scrolled away). Fixes flutter#194718
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October 21, 2026 04:18
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This pull request modifies RenderTwoDimensionalViewport to de-duplicate children present in both _children and _keepAliveBucket maps before calling attach or detach on them. Additionally, a regression test has been added to verify that kept-alive children are not detached twice when the viewport is removed. I have no further feedback to provide.
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A kept-alive child of
RenderTwoDimensionalViewportis present in both_childrenand_keepAliveBucket(_cacheKeepAlivesadds it to the bucket without removing it from_children).attachanddetachlooped over both maps, so such a child was attached/detached twice, tripping the_owner != nullassertion inRenderObject.detach(e.g. aTableViewinside aListViewwith a selected cell scrolled away, or any cell usingAutomaticKeepAliveClientMixin).This de-duplicates the children in
attachanddetach. Removing the child from_childrenin_cacheKeepAliveswas tried first but breaks existing keep-alive tests, since other code relies on it staying there.Fixes #194718
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