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Web: value={0} with a negative minimumValue renders the thumb at the minimum

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@huytdps13400 已經在處理了。

開始於 2026年10月3日。

  • #829 來自 @huytdps13400 —— 未關閉

評估

難度
2/5
預估耗時
1-3 小時
新手友好度
78/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
活躍
技術堆疊
react-native, typescript
領域
frontend, web-dev

研究方向

從 package/src/RNCSliderNativeComponent.web.tsx 開始，特別查看第 81 行附近的初始狀態，以及第 163-171 行附近的重新同步 effect。重現提供的負最小值範例，然後確認明確指定的值 value={0} 會以零呈現，而非受控情況不會意外重設。

由索引模型根據 Issue 內容生成。

描述

Environment

  • @react-native-community/slider: 5.2.1 (also present on main at the time of writing)
  • Platform: web (react-native-web 0.21.2)
  • react: 19.2.3 · react-native: 0.86.3 · Expo SDK 57
  • New architecture: yes (Expo newArchEnabled is unconditional in SDK 57) — but this is a web-only code path, so the architecture is not relevant

Description

On web, a slider rendered with value={0} and a negative minimumValue paints its thumb at the minimum instead of at zero.

The value itself is fine — onValueChange reports correctly, and every number the app derives from the slider is right. Only the thumb position is wrong, and it stays wrong until the user drags it, at which point it starts behaving. So the failure looks like a rendering quirk rather than a state bug, which makes it easy to dismiss.

It is quite easy to hit in practice: any bipolar control that rests at zero does. Mine is a turntable-style pitch fader (-8 … +8, resting at 0), which means it was wrong on every load.

Reproducible Demo

import Slider from '@react-native-community/slider';

// Thumb renders hard left. Expected: centred.
<Slider minimumValue={-8} maximumValue={8} value={0} />

// Both of these are fine, which isolates it to the value being exactly zero
// against a negative minimum:
<Slider minimumValue={-8} maximumValue={8} value={0.1} />
<Slider minimumValue={0}  maximumValue={16} value={8} />

Cause

Two things combine, both in package/src/RNCSliderNativeComponent.web.tsx.

1. The initial state is seeded with || (L81):

const [value, setValue] = React.useState(initialValue || minimumValue);

0 is falsy, so value={0} seeds the internal state at minimumValue rather than at 0.

This cannot be fixed with ?? alone, because value is already defaulted at the destructure (L55):

value: initialValue = 0,

so by the time that line runs, "no value prop" and value={0} are indistinguishable — both are 0.

2. The resync effect cannot recover it (L163-L171):

const lastInitialValue = React.useRef<number>(0);
// ...
if (initialValue !== lastInitialValue.current) {
  lastInitialValue.current = initialValue;
  const newValue = updateValue(initialValue);
  animationValues.val.setValue(newValue);
}

The ref starts at 0, so for initialValue === 0 the guard evaluates 0 !== 0 — false. The effect never runs and the wrong initial state is never corrected.

I appreciate the guard is deliberate; the comment above it explains that it exists because initialValue gets defaulted to 0 by Slider, and without it the value resets constantly when the slider is uncontrolled. Any fix wants to keep that property.

Suggested fix

Distinguish "no value prop" from value={0} by not defaulting at the destructure, and track the same distinction in the ref:

value: initialValue,                                    // no ` = 0`
// ...
const [value, setValue] = React.useState(initialValue ?? minimumValue);
const lastInitialValue = React.useRef<number | undefined>(initialValue);
// ...
if (initialValue !== undefined && initialValue !== lastInitialValue.current) {
  lastInitialValue.current = initialValue;
  const newValue = updateValue(initialValue);
  animationValues.val.setValue(newValue);
}

That keeps the uncontrolled case from being reset (the effect still does nothing when no value is passed) while letting an explicit value={0} through.

I have not sent a PR since the change touches the uncontrolled path and you will have a clearer view than I do of what that should do; happy to open one if the approach looks right.

Workaround

For anyone hitting this before it is fixed: shift the domain so zero is not the resting value, and convert at the boundary.

// fader units 0 … 2R, presented as -R … +R
<Slider
  minimumValue={0}
  maximumValue={range * 2}
  value={pitch + range}
  onValueChange={(v) => setPitch(v - range)}
/>

The only value that still lands on 0 is the control fully down, where minimumValue is also 0, so the falsy branch produces the correct result anyway.

主要語言
TypeScript
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3 天 4 小時
30 天內合併 PR
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環境準備

從這裡開始

  1. 先讀完整個 Issue，再讀專案的貢獻指南。
  2. 在 Issue 下留言說明你要接手 —— 這能避免兩個人做同樣的事。
  3. Fork 儲存庫，在一個分支上完成修改。
  4. 送出 Pull Request，並在描述裡引用這個 Issue 編號。

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