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fix: eliminate HeaderBase layout flicker with useLayoutEffect #25929

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georgewrmarshall wants to merge 2 commits into from
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fix: eliminate HeaderBase layout flicker with useLayoutEffect #25929

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b3b8877
fix: eliminate HeaderBase layout flicker with useLayoutEffect
georgewrmarshall Feb 10, 2026
09b9bc1
fix: add onLayout fallback to HeaderBase measurement
georgewrmarshall Feb 10, 2026
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62 changes: 52 additions & 10 deletions app/component-library/components/HeaderBase/HeaderBase.tsx
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
// Third party dependencies.
import React, { useCallback, useState } from 'react';
import React, { useRef, useState, useLayoutEffect, useCallback } from 'react';
import { View, LayoutChangeEvent } from 'react-native';

// External dependencies.
Expand Down Expand Up @@ -42,17 +42,11 @@ const HeaderBase: React.FC<HeaderBaseProps> = ({
const tw = useTailwind();
const insets = useSafeAreaInsets();

const startAccessoryRef = useRef<View>(null);
const endAccessoryRef = useRef<View>(null);
const [startAccessoryWidth, setStartAccessoryWidth] = useState(0);
const [endAccessoryWidth, setEndAccessoryWidth] = useState(0);

const handleStartAccessoryLayout = useCallback((e: LayoutChangeEvent) => {
setStartAccessoryWidth(e.nativeEvent.layout.width);
}, []);

const handleEndAccessoryLayout = useCallback((e: LayoutChangeEvent) => {
setEndAccessoryWidth(e.nativeEvent.layout.width);
}, []);

// Determine alignment and text variant based on variant prop
const isLeftAligned = variant === HeaderBaseVariant.Display;
const textVariant = HEADERBASE_VARIANT_TEXT_VARIANTS[variant];
Expand All @@ -63,6 +57,53 @@ const HeaderBase: React.FC<HeaderBaseProps> = ({
endAccessory || (endButtonIconProps && endButtonIconProps.length > 0);
const hasAnyAccessory = hasStartContent || hasEndContent;

// Attempt synchronous measurement on mount/updates to reduce flicker
useLayoutEffect(() => {
if (startAccessoryRef.current) {
startAccessoryRef.current.measure((_x, _y, width, _height) => {
if (width > 0 && width !== startAccessoryWidth) {
setStartAccessoryWidth(width);
}
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@cursor cursor Bot Feb 10, 2026

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Guard width > 0 prevents resetting stale accessory widths

High Severity

The width > 0 guard in both the measure() callback and the onLayout fallback prevents accessory widths from ever resetting to zero. In Compact variant, when one accessory is removed while the other remains, the wrapper still renders (for centering) but contains no children, resulting in a width-0 layout event. The guard blocks this update, so startAccessoryWidth or endAccessoryWidth retains its stale non-zero value. This causes accessoryWrapperWidth via Math.max to use an incorrect measurement, misaligning the title. The previous code had no such guard and unconditionally called setStartAccessoryWidth(e.nativeEvent.layout.width), correctly handling the zero-width case.

Additional Locations (1)

Fix in Cursor Fix in Web

});
}

if (endAccessoryRef.current) {
endAccessoryRef.current.measure((_x, _y, width, _height) => {
if (width > 0 && width !== endAccessoryWidth) {
setEndAccessoryWidth(width);
}
});
}
}, [
startAccessory,
startButtonIconProps,
endAccessory,
endButtonIconProps,
startAccessoryWidth,
endAccessoryWidth,
]);
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@cursor cursor Bot Feb 10, 2026

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State values in useLayoutEffect deps cause extra cycles

Medium Severity

Including startAccessoryWidth and endAccessoryWidth (state values) in the useLayoutEffect dependency array causes the effect to re-run every time a measurement updates the state. Each width change triggers another measure() call that finds the value unchanged and does nothing. The reference pattern in useFeedScrollManager.ts deliberately excludes state from its useLayoutEffect deps to avoid this redundant cycle. Removing these two state entries from the array would eliminate the unnecessary re-execution.

Fix in Cursor Fix in Web


// Fallback onLayout callbacks for when measure() returns 0 or content changes
const handleStartAccessoryLayout = useCallback(
(event: LayoutChangeEvent) => {
const { width } = event.nativeEvent.layout;
if (width > 0 && width !== startAccessoryWidth) {
setStartAccessoryWidth(width);
}
},
[startAccessoryWidth],
);

const handleEndAccessoryLayout = useCallback(
(event: LayoutChangeEvent) => {
const { width } = event.nativeEvent.layout;
if (width > 0 && width !== endAccessoryWidth) {
setEndAccessoryWidth(width);
}
},
[endAccessoryWidth],
);

// For Compact: render both wrappers if any accessory exists (for centering)
// For Display: only render wrappers if their respective accessory exists
const shouldRenderStartWrapper = isLeftAligned
Expand Down Expand Up @@ -150,7 +191,7 @@ const HeaderBase: React.FC<HeaderBaseProps> = ({
}
{...startAccessoryWrapperProps}
>
<View onLayout={handleStartAccessoryLayout}>
<View ref={startAccessoryRef} onLayout={handleStartAccessoryLayout}>
{renderStartContent()}
</View>
</View>
Expand Down Expand Up @@ -182,6 +223,7 @@ const HeaderBase: React.FC<HeaderBaseProps> = ({
{...endAccessoryWrapperProps}
>
<View
ref={endAccessoryRef}
onLayout={handleEndAccessoryLayout}
style={
hasMultipleEndButtons ? tw.style('flex-row gap-2') : undefined
Expand Down
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