react / react/react-native

`alignContent: stretch` doesn't actually stretch rows in a `flexWrap: wrap` layout

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描述

Description

I'm seeing a big discrepency between react native web and iOS/Android for the behavior of alignContent: stretch for views with flexWrap: wrap and flexDirection: column. I noticed the discrepency when I tried to set the alignSelf property of an individual element inside the flex container.

On web, alignContent: stretch works as expected. Each row becomes tall enough that I can align elements individually within their respective row using alignSelf

But on iOS and Android, alignSelf initially seems to have no effect. This is because, even though alignContent: stretch is set, the implicit row containers don't actually stretch out to their full height. Rows begin in their expected positions, but the height of each row is implicitly fit to contents instead of stretching. This means my elements can't align themselves properly — they have nowhere to go, their container is too restricted.

An almost-workaround I found, for example, is to add an empty view inside the flex container that has the desired height of a row — that makes the row stretch out enough so that other elements are visibly aligned correctly. But this isn't a real option for me — first of all, it breaks any layout that depends on the number  I can't guarantee the height or number of any particular element, as I need to build very generically.

Steps to reproduce

See expo snack
In general, I believe:

  1. Create a flex container with "flexDirection": "row", "flexWrap": "wrap", "alignContent": "stretch"
  2. Add a child with "alignSelf": "flex-end", or `"alignSelf": "center"
  3. Observe that alignSelf changes the element's position on web, as expect, but has no effect on ios/android
React Native Version

0.76.3

Affected Platforms

Runtime - iOS, Runtime - Android

Output of npx @react-native-community/cli info
System:
  OS: macOS 14.7.1
  CPU: (8) arm64 Apple M2
  Memory: 154.44 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.14.0
    path: ~/.nvm/versions/node/v22.14.0/bin/node
  Yarn: Not Found
  npm:
    version: 10.9.2
    path: ~/.nvm/versions/node/v22.14.0/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.15.2
    path: /opt/homebrew/lib/ruby/gems/3.3.0/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.1
      - iOS 18.1
      - macOS 15.1
      - tvOS 18.1
      - visionOS 2.1
      - watchOS 11.1
  Android SDK:
    API Levels:
      - "34"
      - "35"
    Build Tools:
      - 33.0.1
      - 34.0.0
      - 35.0.0
    System Images:
      - android-35 | ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2024.2 AI-242.23339.11.2421.12700392
  Xcode:
    version: 16.1/16B40
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.3.6
    path: /opt/homebrew/opt/ruby/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.6
    wanted: 0.76.6
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found
Stacktrace or Logs
N/A — layout bug
Reproducer

https://snack.expo.dev/OT-sH48w22h3vDCqD6nra?platform=ios

Screenshots and Videos

Web (Expected Behavior)
Image

Mobile (Rows are too short, can't align properly)
Image

贡献指南

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从这里开始

  1. 先读完整个 Issue,再读项目的贡献指南。
  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库,在一个分支上完成修改。
  4. 提交 Pull Request,并在描述里引用这个 Issue 编号。

调研方向

从链接的 Expo Snack 复现示例开始,比较使用 alignContent: stretch 的自动换行 flex 容器以及使用 alignSelf 的子元素在 Web、iOS 和 Android 上的结果。完成的标准是原生平台拉伸隐式行,使 alignSelf 能够像在 Web 上一样在每一行中定位子元素。

由索引模型根据 Issue 内容生成。

评估

技术栈
react-native
领域
mobile
Issue 类型
缺陷
难度
4/5
预计耗时
3-5 天
活跃度
活跃
描述清晰度
基本清楚
新手友好度
45/100

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