Skip to content

Improve SizedBox's docs #187208

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
auto-submit merged 1 commit into from
May 28, 2026
+33 −9
Merged

Improve SizedBox's docs #187208

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 33 additions & 9 deletions packages/flutter/lib/src/widgets/basic.dart
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2678,14 +2678,10 @@ class CustomMultiChildLayout extends MultiChildRenderObjectWidget {

/// A box with a specified size.
///
/// If given a child, this widget forces it to have a specific width and/or height.
/// These values will be ignored if this widget's parent does not permit them.
/// For example, this happens if the parent is the screen (forces the child to
/// be the same size as the parent), or another [SizedBox] (forces its child to
/// have a specific width and/or height). This can be remedied by wrapping the
/// child [SizedBox] in a widget that does permit it to be any size up to the
/// size of the parent, such as [Center] or [Align].
/// {@youtube 560 315 https://www.youtube.com/watch?v=EHPu_DzRfqA}
///
/// If given a child, this widget will try to size its child as close to the
/// specified [height] and [width] as possible given the parent's constraints.
/// If either the width or height is null, this widget will try to size itself to
/// match the child's size in that dimension. If the child's size depends on the
/// size of its parent, the height and width must be provided.
Expand All @@ -2698,8 +2694,6 @@ class CustomMultiChildLayout extends MultiChildRenderObjectWidget {
/// sizes itself to fit the parent. It is equivalent to setting [width] and
/// [height] to [double.infinity].
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=EHPu_DzRfqA}
///
/// {@tool snippet}
///
/// This snippet makes the child widget (a [Card] with some [Text]) have the
Expand All @@ -2714,6 +2708,36 @@ class CustomMultiChildLayout extends MultiChildRenderObjectWidget {
/// ```
/// {@end-tool}
///
/// ## Troubleshooting
///
/// ### Why is my [SizedBox] ignored?
///
/// In Flutter's layout protocol constraints go down, and sizes go up.
/// A widget must respect the constraints passed by its parent. This can cause a
/// [SizedBox]'s values to be ignored:
///
/// {@tool snippet}
///
/// This snippet makes the [ColoredBox] size 200x200. The 100x100 size is
/// ignored because it is incompatible with its parent constraints of exactly
/// 200x200:
///
/// ```dart
/// const SizedBox(
/// width: 200.0,
/// height: 200.0,
/// child: SizedBox( // Ignored!
/// width: 100.0,
/// height: 100.0,
/// child: ColoredBox(color: Colors.green),
Comment thread
loic-sharma marked this conversation as resolved.
/// ),
/// )
/// ```
/// {@end-tool}
///
/// This can be fixed by wrapping the child [SizedBox] in a widget that lets
/// it be any size up to the size of the parent, such as [Center] or [Align].
///
/// See also:
///
/// * [ConstrainedBox], a more generic version of this class that takes
Expand Down
Loading