StreamFlex class

A widget that displays its children in a one-dimensional array, supporting negative spacing and collapsed (nullable) children.

StreamFlex allows you to control the axis along which the children are placed (horizontal or vertical). The spacing parameter can be positive (gap between children), zero (flush), or negative (children overlap).

If you know the main axis in advance, consider using StreamRow (horizontal) or StreamColumn (vertical) instead, since that will be less verbose.

Collapsed children

Children built with NullableStatelessWidget, NullableStatefulWidget, or NullableBuilder can return null from their nullableBuild method. When they do, they collapse to zero size and no spacing is allocated for them.

In a regular Row or Column, a zero-size child still occupies a spacing slot. StreamFlex (and its subclasses) detect collapsed children and exclude them from spacing calculations entirely.

{@tool snippet}

A column with 8px spacing where the subtitle conditionally collapses. When showSubtitle is false, only one 8px gap remains between "Title" and "Body" — the collapsed child does not add an extra spacing slot:

StreamColumn(
  spacing: 8,
  children: [
    Text('Title'),
    NullableBuilder(builder: (context) {
      if (!showSubtitle) return null;
      return const Text('Subtitle');
    }),
    Text('Body'),
  ],
)

{@end-tool}

{@tool snippet}

Overlapping avatars with -8px spacing:

StreamRow(
  spacing: -8,
  children: [
    CircleAvatar(child: Text('A')),
    CircleAvatar(child: Text('B')),
    CircleAvatar(child: Text('C')),
  ],
)

{@end-tool}

Layout algorithm

Layout inflexible children with unbounded main-axis constraints.
Distribute remaining main-axis space to flexible children.
Layout flexible children with allocated space.
Cross-axis extent = maximum child cross extent.
Main-axis extent determined by mainAxisSize and constraints.
Position children according to mainAxisAlignment and crossAxisAlignment, applying spacing between each pair.

Collapsed children are excluded from all steps above.

With negative spacing, the total main-axis extent shrinks and children are positioned closer together, producing overlap. Later children in the list paint on top of earlier ones (natural z-order).

Constructors

StreamFlex({Key? key, required Axis direction, MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start, MainAxisSize mainAxisSize = MainAxisSize.min, CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center, TextDirection? textDirection, VerticalDirection verticalDirection = VerticalDirection.down, TextBaseline? textBaseline, Clip clipBehavior = Clip.none, double spacing = 0.0, List<Widget> children = const <Widget>[]}): Creates a flex layout that supports negative spacing.
const

Properties

children → List<Widget>: The widgets below this widget in the tree.
finalinherited
clipBehavior → Clip: How to clip children that extend beyond the widget's bounds.
final
crossAxisAlignment → CrossAxisAlignment: How the children should be placed along the cross axis.
final
direction → Axis: The direction to use as the main axis.
final
hashCode → int: The hash code for this object.
no setterinherited
key → Key?: Controls how one widget replaces another widget in the tree.
finalinherited
mainAxisAlignment → MainAxisAlignment: How the children should be placed along the main axis.
final
mainAxisSize → MainAxisSize: How much space should be occupied in the main axis.
final
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
spacing → double: The amount of space between children along the main axis.
final
textBaseline → TextBaseline?: If aligning items according to their baseline, which baseline to use.
final
textDirection → TextDirection?: Determines the order to lay children out horizontally and how to interpret start and end in the horizontal direction.
final
verticalDirection → VerticalDirection: Determines the order to lay children out vertically and how to interpret start and end in the vertical direction.
final

Methods

createElement() → MultiChildRenderObjectElement: RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
createRenderObject(BuildContext context) → RenderFlex: 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.
inherited
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
getEffectiveTextDirection(BuildContext context) → TextDirection?: The resolved text direction for layout.
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 RenderFlex 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