ConstraintsTransformBox class

A container widget that applies an arbitrary transform to its constraints, and sizes its child using the resulting BoxConstraints, optionally clipping, or treating the overflow as an 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 clipBehavior is Clip.none and 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:

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

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 and expands to fit them.