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 in left-to-right environments and the top-right corner in right-to-left environments). 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.

Stack(
  children: <Widget>[
    Container(
      width: 100,
      height: 100,
      color: Colors.red,
    ),
    Container(
      width: 90,
      height: 90,
      color: Colors.green,
    ),
    Container(
      width: 80,
      height: 80,
      color: Colors.blue,
    ),
  ],
)

SizedBox(
  width: 250,
  height: 250,
  child: Stack(
    children: <Widget>[
      Container(
        width: 250,
        height: 250,
        color: Colors.white,
      ),
      Container(
        padding: const EdgeInsets.all(5.0),
        alignment: Alignment.bottomCenter,
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.topCenter,
            end: Alignment.bottomCenter,
            colors: <Color>[
              Colors.black.withAlpha(0),
              Colors.black12,
              Colors.black45
            ],
          ),
        ),
        child: const Text(
          'Foreground Text',
          style: TextStyle(color: Colors.white, fontSize: 20.0),
        ),
      ),
    ],
  ),
)

See also:

• Align, which sizes itself based on its child's size and positions the child according to an 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.
• The catalog of layout widgets.

Inheritance

• Object
• DiagnosticableTree
• Widget
• RenderObjectWidget
• MultiChildRenderObjectWidget
• Stack

Constructors

Stack({Key? key, AlignmentGeometry alignment = AlignmentDirectional.topStart, TextDirection? textDirection, StackFit fit = StackFit.loose, Clip clipBehavior = Clip.hardEdge, List<Widget> children = const <Widget>[]})

Creates a stack layout widget.

const

Properties

alignment → AlignmentGeometry

How to align the non-positioned and partially-positioned children in the stack.

final

children → List<Widget>

The widgets below this widget in the tree.

finalinherited

clipBehavior → Clip

The content will be clipped (or not) according to this option.

final

fit → StackFit

How to size the non-positioned children in the stack.

final

hashCode → int

The hash code for this object.

no setterinherited

key → Key?

Controls how one widget replaces another widget in the tree.

finalinherited

runtimeType → Type

A representation of the runtime type of the object.

no setterinherited

textDirection → TextDirection?

The text direction with which to resolve alignment.

final

Methods

createElement() → MultiChildRenderObjectElement

RenderObjectWidgets always inflate to a RenderObjectElement subclass.

inherited

createRenderObject(BuildContext context) → RenderStack

Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget.

override

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.

override

didUnmountRenderObject(covariant RenderObject renderObject) → void

This method is called when a RenderObject that was previously associated with this widget is removed from the render tree. The provided RenderObject will be of the same type as the one created by this widget's createRenderObject method.

inherited

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

updateRenderObject(BuildContext context, covariant 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.

override

Operators

operator ==(Object other) → bool

The equality operator.

inherited