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Nick GerlemanandFacebook GitHub Bot
a6bc77cd94
Summary: When `getItemLayout` is not supplied, VirtualizedList doesn't know the measurements for its child items ahead of time. It caches most recent cell measurements so that an item which is virtualized away is associated with its correct height. VirtualizedList will not consume space for an item it has not yet rendered/knows measurements for. This also means an initially created list will only take up the height of its `initialNumToRender()`. This can cause scroll jumping for the scenario of nested VirtualizedLists of the same orientation, since a virtualized away child list will shrink (compared to the spacer), then re-expand, once returned to. There is logic in the VirtualizedList constructor to load cached frame metrics based on supplied listKey, to enable reloading most recent state. Though locally it seems to be reading the context too early in the lifecycle (compared to other successful checks during componentDidMount, render). It was moved from `componentDidMount` to `constructor` as part of the initial change (https://www.internalfb.com/diff/D6330846 (https://github.com/facebook/react-native/commit/2668dc8e1be7bf93e65ca2e11c87cbeef3310c3e)?dst_version_fbid=131968984136932&transaction_fbid=1578362385612542), and I think has likely been unreliable or dead since. Restoring state was the only usage of a durable key for nested lists beyond their lifetime. So removing the dead code lets us remove the need for a `listKey`, which has been error-prone. This still leaves the problem present since inception, but there may be alternate solutions like scroll anchoring. Changelog: [Internal][Removed] - Remove dead code for restoring state to nested VirtualizedList Reviewed By: ryancat Differential Revision: D39466678 fbshipit-source-id: fc2f39802e5cdf9b920974333be64c74211b99a9