[bvaughn]

Pixel-based constraints (e.g. minSize="200px") are converted to percentages using the group size that the group's ResizeObserver last measured. If the group was resized and an imperative method ran before that observer did (e.g. from an application's own ResizeObserver), the layout was validated against the old size's constraints. The clamped result was then saved as the requested layout, so it stayed wrong after the observer ran.

The fix:

• Moved the ResizeObserver's sync step into a new syncAxisStateToCurrentSize() helper. It measures the group, recalculates the pixel-based constraints, and re-derives the layout from the requested layout. It returns the new state without saving it.
• The observer and the imperative methods above now use the helper. Imperative methods sync before validating, and save the synced state and their own change together, so onLayoutChange fires once per call.
• calculateItemConstraints() accepts an already-measured size, so each sync measures the panels once.

Behavior changes:

• An imperative call on a group that has grown since its observer last ran now sees the current size.
• If a group was hidden at mount and becomes visible before its observer runs, setLayout() now applies the layout instead of ignoring it.
• Panel.resize() on a hidden group now uses the last measured size instead of dividing by zero.

Note

Each imperative call now reads the panels' offsetWidth/offsetHeight once. This can make the browser recalculate layout if a change is pending.

Fixes #770

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Project	Deployment	Actions	Updated
react-resizable-panels	Ready	Preview	Oct 20, 2026 10:48pm UTC