Samuel SuslaandFacebook GitHub Bot
43b2c6dd85
Summary:
Changelog: [Internal]
# Problem
## Step 1
JS clones a node that has size {100, 100} and changes props that cause the node to increase size to {200, 200}. JS holds pointer to this node.
Now, the size (stored in LayoutableShadowNode.layoutMetrics_) changes after Yoga layout is triggered.
However, the node gets cloned inside State Reconciliation before Yoga layout phase. The JS pointer points to a node with size {100, 100}, not to a node with size {200, 200}.
## Step 2
Again, JS clones node (with old reference, therefore gets old layoutMetrics_ with size {100, 100}) and it changes props that cause the node to decrease its size back to {100, 100}.
We go all the way to Yoga layout and looking for nodes that have been affected by the node. The node, affected by the layout because it went from {200, 200} to {100, 100}, will be evaluated as not affected. This causes onLayout event to not be fired.
# Fix
We can safely remove the frame equality check (please see below). This can be done because we already check for equality before dispatching onLayout. It happens here:
https://www.internalfb.com/intern/diffusion/FBS/browsefile/master/xplat/js/react-native-github/ReactCommon/react/renderer/components/view/ViewEventEmitter.cpp?commit=881853eb0c42625fd0812bd2652bf36fcbd614ee&lines=43
As far as I know, `affectedNodes` isn't used for anything else besides dispatching onLayout.
# Discussion
This problem manifests itself only when a node has two different sizes that it flips between. To better understand this, please watch the video in Test plan labelled "before". Notice how the text has 2 different values that it flips between.
Here is a code that was affected by it https://fburl.com/diffusion/3hwo0iy5
If you inspect it closely, you will notice that it depends on `onLayout` to return correct value to calculate offset from left.
Reviewed By: JoshuaGross
Differential Revision: D22999891
fbshipit-source-id: e2d0f5771c1bf3cd788e5e9da0155c92e33fb84e
React Native
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