A widget that positions its children relative to the edges of its box.

This class is useful if you want to overlap several children in a simple way, for example having some text and an image, overlaid with a gradient and a button attached to the bottom.

Each child of a Stack widget is either positioned or non-positioned. Positioned children are those wrapped in a Positioned widget that has at least one non-null property. The stack sizes itself to contain all the non-positioned children, which are positioned according to alignment (which defaults to the top-left corner). The positioned children are then placed relative to the stack according to their top, right, bottom, and left properties.

The stack paints its children in order with the first child being at the bottom. If you want to change the order in which the children paint, you can rebuild the stack with the children in the new order. If you reorder the children in this way, consider giving the children non-null keys. These keys will cause the framework to move the underlying objects for the children to their new locations rather than recreate them at their new location.

For more details about the stack layout algorithm, see RenderStack.

If you want to lay a number of children out in a particular pattern, or if you want to make a custom layout manager, you probably want to use CustomMultiChildLayout instead. In particular, when using a Stack you can't position children relative to their size or the stack's own size.

See also:

  • Align, which sizes itself based on its child's size and positions the child according to a Alignment value.
  • CustomSingleChildLayout, which uses a delegate to control the layout of a single child.
  • CustomMultiChildLayout, which uses a delegate to position multiple children.
  • Flow, which provides paint-time control of its children using transform matrices.
Inheritance
Implemented by

Constructors

Stack({Key key, AlignmentGeometry alignment: AlignmentDirectional.topStart, TextDirection textDirection, StackFit fit: StackFit.loose, Overflow overflow: Overflow.clip, List<Widget> children: const [] })
Creates a stack layout widget. [...]

Properties

alignment AlignmentGeometry
How to align the non-positioned children in the stack. [...]
final
fit StackFit
How to size the non-positioned children in the stack. [...]
final
overflow Overflow
Whether overflowing children should be clipped. See Overflow. [...]
final
textDirection TextDirection
The text direction with which to resolve alignment. [...]
final
children List<Widget>
The widgets below this widget in the tree. [...]
final, inherited
hashCode int
The hash code for this object. [...]
read-only, inherited
key Key
Controls how one widget replaces another widget in the tree. [...]
final, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited

Methods

createRenderObject(BuildContext context) RenderStack
Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget. [...]
debugFillProperties(DiagnosticPropertiesBuilder description) → void
updateRenderObject(BuildContext context, RenderStack renderObject) → void
Copies the configuration described by this RenderObjectWidget to the given RenderObject, which will be of the same type as returned by this object's createRenderObject. [...]
createElement() MultiChildRenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
didUnmountRenderObject(RenderObject renderObject) → void
A render object previously associated with this widget has been removed from the tree. The given RenderObject will be of the same type as returned by this object's createRenderObject.
@protected, 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 toStringDeep. [...]
inherited
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns 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 ==(other) bool
The equality operator. [...]
inherited