ConstraintsTransformBoxModifier class

A container widget that applies an arbitrary transform to its constraints, and sizes its child using the resulting BoxConstraints, treating any overflow as error.

This container sizes its child using a BoxConstraints created by applying constraintsTransform to its own constraints. This container will then attempt to adopt the same size, within the limits of its own constraints. If it ends up with a different size, it will align the child based on alignment. If the container cannot expand enough to accommodate the entire child, the child will be clipped if clipBehavior is not Clip.none.

In debug mode, if the child overflows the container, a warning will be printed on the console, and black and yellow striped areas will appear where the overflow occurs.

When child is null, this widget becomes as small as possible and never overflows

This widget can be used to ensure some of child's natural dimensions are honored, and get an early warning otherwise during development. For instance, if child requires a minimum height to fully display its content, constraintsTransform can be set to maxHeightUnconstrained, so that if the parent RenderObject fails to provide enough vertical space, a warning will be displayed in debug mode, while still allowing child to grow vertically:

{@tool snippet} In the following snippet, the Card is guaranteed to be at least as tall as its "natural" height. Unlike UnconstrainedBox, it will become taller if its "natural" height is smaller than 40 px. If the Container isn't high enough to show the full content of the Card, in debug mode a warning will be given.

Container(
  constraints: const BoxConstraints(minHeight: 40, maxHeight: 100),
  alignment: Alignment.center,
  child: const ConstraintsTransformBox(
    constraintsTransform: ConstraintsTransformBox.maxHeightUnconstrained,
    child: Card(child: Text('Hello World!')),
  )
)

{@end-tool}

See also:

  • ConstrainedBox, which renders a box which imposes constraints on its child.
  • OverflowBox, a widget that imposes additional constraints on its child, and allows the child to overflow itself.
  • UnconstrainedBox which allows its children to render themselves unconstrained, expands to fit them, and considers overflow to be an error.
Inheritance
Available extensions

Constructors

ConstraintsTransformBoxModifier({Key? key, Widget? child, TextDirection? textDirection, AlignmentGeometry alignment = Alignment.center, required BoxConstraintsTransform constraintsTransform, Clip clipBehavior = Clip.none, String debugTransformType = ''})
Creates a widget that uses a function to transform the constraints it passes to its child. If the child overflows the parent's constraints, a warning will be given in debug mode.
const

Properties

alignment → AlignmentGeometry
The alignment to use when laying out the child, if it has a different size than this widget.
final
clipBehavior → Clip
The content will be clipped (or not) according to this option.
final
constraintsTransform → BoxConstraintsTransform
The function used to transform the incoming BoxConstraints, to size child.
final
hashCode → int
The hash code for this object.
no setterinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
modifierKey → Key?
The actual key of the widget, which Modifier wrapped
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
textDirection → TextDirection?
The text direction to use when interpreting the alignment if it is an AlignmentDirectional.
final

Methods

build(BuildContext context) → Widget
Describes the part of the user interface represented by this widget.
inherited
buildWithChild(BuildContext context, Widget? child) → Widget
A build method that receives an extra child parameter.
override
createElement() → SingleChildStatelessElement
Create a SingleChildStatelessElement
inherited
debugDescribeChildren() → List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
modified() → Modifier

Available on Widget, provided by the ModifierTransformer extension

Transform normal widget to Modifier
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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, int wrapWidth = 65}) → 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.
inherited