SizedBox class

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.

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.

If not given a child, SizedBox will try to size itself as close to the specified height and width as possible given the parent's constraints. If height or width is null or unspecified, it will be treated as zero.

The SizedBox.expand constructor can be used to make a SizedBox that sizes itself to fit the parent. It is equivalent to setting width and height to double.infinity.

const SizedBox(
  width: 200.0,
  height: 300.0,
  child: Card(child: Text('Hello World!')),
)

See also:

• ConstrainedBox, a more generic version of this class that takes arbitrary BoxConstraints instead of an explicit width and height.
• UnconstrainedBox, a container that tries to let its child draw without constraints.
• FractionallySizedBox, a widget that sizes its child to a fraction of the total available space.
• AspectRatio, a widget that attempts to fit within the parent's constraints while also sizing its child to match a given aspect ratio.
• FittedBox, which sizes and positions its child widget to fit the parent according to a given BoxFit discipline.
• The catalog of layout widgets.
• Understanding constraints, an in-depth article about layout in Flutter.