PreferredSize class Null safety
A widget with a preferred size.
This widget does not impose any constraints on its child, and it doesn't affect the child's layout in any way. It just advertises a preferred size which can be used by the parent.
Parents like Scaffold use PreferredSizeWidget to require that their
children implement that interface. To give a preferred size to an arbitrary
widget so that it can be used in a child property of that type, this
widget, PreferredSize, can be used.
Widgets like AppBar implement a PreferredSizeWidget, so that this PreferredSize widget is not necessary for them.
This sample shows a custom widget, similar to an AppBar, which uses a
PreferredSize widget, with its height set to 80 logical pixels.
Changing the PreferredSize can be used to change the height
of the custom app bar.
To create a local project with this code sample, run:
flutter create --sample=widgets.PreferredSize.1 mysample
flutter create --sample=widgets.PreferredSize.1 mysample
See also:
- AppBar.bottom and Scaffold.appBar, which require preferred size widgets.
- PreferredSizeWidget, the interface which this widget implements to expose its preferred size.
- AppBar and TabBar, which implement PreferredSizeWidget.
- Inheritance
-
- Object
- DiagnosticableTree
- Widget
- StatelessWidget
- PreferredSize
- Implemented types
Constructors
- PreferredSize({Key? key, required Widget child, required Size preferredSize})
-
Creates a widget that has a preferred size that the parent can query.
const
Properties
- child → Widget
-
The widget below this widget in the tree.
final
- hashCode → int
- The hash code for this object.
- key → Key?
-
Controls how one widget replaces another widget in the tree.
finalinherited
- preferredSize → Size
-
The size this widget would prefer if it were otherwise unconstrained.
final
- runtimeType → Type
-
A representation of the runtime type of the object.
read-onlyinherited
Methods
-
build(
BuildContext context) → Widget -
Describes the part of the user interface represented by this widget.
override
-
createElement(
) → StatelessElement -
Creates a StatelessElement to manage this widget's location in the tree.
inherited
-
debugDescribeChildren(
) → List< DiagnosticsNode> -
Returns a list of
DiagnosticsNodeobjects describing this node's children.protected">@protectedinherited -
debugFillProperties(
DiagnosticPropertiesBuilder properties) → void -
Add additional properties associated with the node.
inherited
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent method or property is accessed.
inherited
-
toDiagnosticsNode(
{String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode -
Returns a debug representation of the object that is used by debugging
tools and by DiagnosticsNode.toStringDeep.
inherited
-
toString(
{DiagnosticLevel minLevel = DiagnosticLevel.info}) → String -
A string representation of this object.
inherited
-
toStringDeep(
{String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a string representation of this node and its descendants.
inherited
-
toStringShallow(
{String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a one-line detailed description of the object.
inherited
-
toStringShort(
) → String -
A short, textual description of this widget.
inherited
Operators
-
operator ==(
Object other) → bool -
The equality operator.
nonVirtual">@nonVirtualinherited