WaterfallFlow class

create by zmtzawqlp on 2019/11/9

A scrollable, 2D array of widgets whose size is variable in the main axis.

The main axis direction of a grid is the direction in which it scrolls (the scrollDirection).

The most commonly used waterfall layouts are WaterfallFlow.count, which creates a layout with a fixed number of tiles in the cross axis.

To create a grid with a large (or infinite) number of children, use the WaterfallFlow.builder constructor with a SliverWaterfallFlowDelegate for the gridDelegate.

To use a custom SliverWaterfallFlowDelegate, use WaterfallFlow.custom.

To create a linear array of children, use a ListView.

To control the initial scroll offset of the scroll view, provide a controller with its ScrollController.initialScrollOffset property set.

Transitioning to CustomScrollView

A WaterfallFlow is basically a CustomScrollView with a single SliverWaterfallFlow in its CustomScrollView.slivers property.

If WaterfallFlow is no longer sufficient, for example because the scroll view is to have both a grid and a list, or because the grid is to be combined with a SliverAppBar, etc, it is straight-forward to port code from using WaterfallFlow to using CustomScrollView directly.

The key, scrollDirection, reverse, controller, primary, physics, and shrinkWrap properties on WaterfallFlow map directly to the identically named properties on CustomScrollView.

The CustomScrollView.slivers property should be a list containing just a SliverWaterfallFlow.

The childrenDelegate property on WaterfallFlow corresponds to the SliverWaterfallFlow.gridDelegate property, and the gridDelegate property on the WaterfallFlow corresponds to the SliverWaterfallFlow.gridDelegate property.

The WaterfallFlow and WaterfallFlow.count constructors' children arguments correspond to the childrenDelegate being a SliverChildListDelegate with that same argument. The WaterfallFlow.builder constructor's itemBuilder and childCount arguments correspond to the childrenDelegate being a SliverChildBuilderDelegate with the matching arguments.

The WaterfallFlow.count constructors create custom grid delegates, and have equivalently named constructor on SliverWaterfallFlow to ease the transition: SliverWaterfallFlow.count respectively.

The padding property corresponds to having a SliverPadding in the CustomScrollView.slivers property instead of the grid itself, and having the SliverWaterfallFlow instead be a child of the SliverPadding.

By default, ListView will automatically pad the list's scrollable extremities to avoid partial obstructions indicated by MediaQuery's padding. To avoid this behavior, override with a zero padding property.

Once code has been ported to use CustomScrollView, other slivers, such as SliverList or SliverAppBar, can be put in the CustomScrollView.slivers list.

{@tool snippet} This example demonstrates how to create a WaterfallFlow with two columns. The children are spaced apart using the crossAxisSpacing and mainAxisSpacing properties.

The WaterfallFlow displays six children with different background colors and heights arranged in two columns

WaterfallFlow.count(
  primary: false,
  padding: const EdgeInsets.all(20),
  crossAxisSpacing: 10,
  mainAxisSpacing: 10,
  crossAxisCount: 2,
  children: <Widget>[
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text("0.He'd have you all unravel at the"),
      color: Colors.teal[100],
      height: 50.0,
    ),
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text('1.Heed not the rabble'),
      color: Colors.teal[200],
      height: 70.0,
    ),
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text('2.Sound of screams but the'),
      color: Colors.teal[300],
      height: 90.0,
    ),
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text('3.Who scream'),
      color: Colors.teal[400],
      height: 60.0,
    ),
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text('4.Revolution is coming...'),
      color: Colors.teal[500],
      height: 80.0,
    ),
    Container(
      padding: const EdgeInsets.all(8),
      child: const Text('5.Revolution, they...'),
      color: Colors.teal[600],
      height: 100.0,
    ),
  ],
)

{@end-tool}

{@tool snippet} This example shows how to create the same grid as the previous example using a CustomScrollView and a SliverWaterfallFlow.

The CustomScrollView contains a SliverWaterfallFlow that displays six children with different background colors and heights arranged in two columns

CustomScrollView(
  primary: false,
  slivers: <Widget>[
    SliverPadding(
      padding: const EdgeInsets.all(20),
      sliver: SliverWaterfallFlow.count(
        crossAxisSpacing: 10,
        mainAxisSpacing: 10,
        crossAxisCount: 2,
        children: <Widget>[
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text("0.He'd have you all unravel at the"),
            color: Colors.green[100],
            height: 50.0,
          ),
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text('1.Heed not the rabble'),
            color: Colors.green[200],
            height: 70.0,
          ),
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text('2.Sound of screams but the'),
            color: Colors.green[300],
            height: 90.0,
          ),
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text('3.Who scream'),
            color: Colors.green[400],
            height: 60.0,
          ),
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text('4.Revolution is coming...'),
            color: Colors.green[500],
            height: 80.0,
          ),
          Container(
            padding: const EdgeInsets.all(8),
            child: const Text('5.Revolution, they...'),
            color: Colors.green[600],
            height: 100.0,
          ),
        ],
      ),
    ),
  ],
)

{@end-tool}

See also:

Inheritance

Constructors

WaterfallFlow({Key? key, Axis scrollDirection = Axis.vertical, bool reverse = false, ScrollController? controller, bool? primary, ScrollPhysics? physics, bool shrinkWrap = false, EdgeInsetsGeometry? padding, required SliverWaterfallFlowDelegate gridDelegate, bool addAutomaticKeepAlives = true, bool addRepaintBoundaries = true, bool addSemanticIndexes = true, double? cacheExtent, List<Widget> children = const <Widget>[], int? semanticChildCount, DragStartBehavior dragStartBehavior = DragStartBehavior.start, ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual, String? restorationId, Clip clipBehavior = Clip.hardEdge})
Creates a scrollable, 2D array of widgets whose size is variable in the main axis with a custom SliverWaterfallFlowDelegate.
WaterfallFlow.builder({Key? key, Axis scrollDirection = Axis.vertical, bool reverse = false, ScrollController? controller, bool? primary, ScrollPhysics? physics, bool shrinkWrap = false, EdgeInsetsGeometry? padding, required SliverWaterfallFlowDelegate gridDelegate, required IndexedWidgetBuilder itemBuilder, int? itemCount, bool addAutomaticKeepAlives = true, bool addRepaintBoundaries = true, bool addSemanticIndexes = true, double? cacheExtent, int? semanticChildCount, DragStartBehavior dragStartBehavior = DragStartBehavior.start, ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual, String? restorationId, Clip clipBehavior = Clip.hardEdge})
Creates a scrollable, 2D array of widgets whose size is variable in the main axis that are created on demand.
WaterfallFlow.count({Key? key, Axis scrollDirection = Axis.vertical, bool reverse = false, ScrollController? controller, bool? primary, ScrollPhysics? physics, bool shrinkWrap = false, EdgeInsetsGeometry? padding, required int crossAxisCount, double mainAxisSpacing = 0.0, double crossAxisSpacing = 0.0, bool addAutomaticKeepAlives = true, bool addRepaintBoundaries = true, bool addSemanticIndexes = true, double? cacheExtent, List<Widget> children = const <Widget>[], int? semanticChildCount, DragStartBehavior dragStartBehavior = DragStartBehavior.start, ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual, LastChildLayoutTypeBuilder? lastChildLayoutTypeBuilder, CollectGarbage? collectGarbage, ViewportBuilder? viewportBuilder, bool closeToTrailing = false, String? restorationId, Clip clipBehavior = Clip.hardEdge})
Creates a scrollable, 2D array of widgets whose size is variable in the main axis with a fixed number of tiles in the cross axis.
WaterfallFlow.custom({Key? key, Axis scrollDirection = Axis.vertical, bool reverse = false, ScrollController? controller, bool? primary, ScrollPhysics? physics, bool shrinkWrap = false, EdgeInsetsGeometry? padding, required SliverWaterfallFlowDelegate gridDelegate, required SliverChildDelegate childrenDelegate, double? cacheExtent, int? semanticChildCount, DragStartBehavior dragStartBehavior = DragStartBehavior.start, ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual, String? restorationId, Clip clipBehavior = Clip.hardEdge})
Creates a scrollable, 2D array of widgets whose size is variable in the main axis with both a custom SliverGridDelegate and a custom SliverChildDelegate.
const
WaterfallFlow.extent({Key? key, Axis scrollDirection = Axis.vertical, bool reverse = false, ScrollController? controller, bool? primary, ScrollPhysics? physics, bool shrinkWrap = false, EdgeInsetsGeometry? padding, required double maxCrossAxisExtent, double mainAxisSpacing = 0.0, double crossAxisSpacing = 0.0, bool addAutomaticKeepAlives = true, bool addRepaintBoundaries = true, bool addSemanticIndexes = true, List<Widget> children = const <Widget>[], int? semanticChildCount, DragStartBehavior dragStartBehavior = DragStartBehavior.start, ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual, LastChildLayoutTypeBuilder? lastChildLayoutTypeBuilder, CollectGarbage? collectGarbage, ViewportBuilder? viewportBuilder, bool closeToTrailing = false, String? restorationId, Clip clipBehavior = Clip.hardEdge})
Creates a scrollable, 2D array of widgets in masonry layout with tiles that each have a maximum cross-axis extent.

Properties

anchor double
The relative position of the zero scroll offset.
finalinherited
cacheExtent double?
The viewport has an area before and after the visible area to cache items that are about to become visible when the user scrolls.
finalinherited
center Key?
The first child in the GrowthDirection.forward growth direction.
finalinherited
childrenDelegate SliverChildDelegate
A delegate that provides the children for the WaterfallFlow.
final
clipBehavior Clip
The content will be clipped (or not) according to this option.
finalinherited
controller ScrollController?
An object that can be used to control the position to which this scroll view is scrolled.
finalinherited
dragStartBehavior DragStartBehavior
Determines the way that drag start behavior is handled.
finalinherited
gridDelegate SliverWaterfallFlowDelegate
A delegate that controls the masonry layout of the children within the WaterfallFlow.
final
hashCode int
The hash code for this object.
no setterinherited
hitTestBehavior HitTestBehavior
Defines the behavior of gesture detector used in this Scrollable.
finalinherited
key Key?
Controls how one widget replaces another widget in the tree.
finalinherited
keyboardDismissBehavior ScrollViewKeyboardDismissBehavior
ScrollViewKeyboardDismissBehavior the defines how this ScrollView will dismiss the keyboard automatically.
finalinherited
padding EdgeInsetsGeometry?
The amount of space by which to inset the children.
finalinherited
physics ScrollPhysics?
How the scroll view should respond to user input.
finalinherited
primary bool?
Whether this is the primary scroll view associated with the parent PrimaryScrollController.
finalinherited
restorationId String?
Restoration ID to save and restore the scroll offset of the scrollable.
finalinherited
reverse bool
Whether the scroll view scrolls in the reading direction.
finalinherited
runtimeType Type
A representation of the runtime type of the object.
no setterinherited
scrollBehavior ScrollBehavior?
A ScrollBehavior that will be applied to this widget individually.
finalinherited
scrollDirection Axis
The Axis along which the scroll view's offset increases.
finalinherited
semanticChildCount int?
The number of children that will contribute semantic information.
finalinherited
shrinkWrap bool
Whether the extent of the scroll view in the scrollDirection should be determined by the contents being viewed.
finalinherited

Methods

build(BuildContext context) Widget
Describes the part of the user interface represented by this widget.
inherited
buildChildLayout(BuildContext context) Widget
Subclasses should override this method to build the layout model.
override
buildSlivers(BuildContext context) List<Widget>
Build the list of widgets to place inside the viewport.
inherited
buildViewport(BuildContext context, ViewportOffset offset, AxisDirection axisDirection, List<Widget> slivers) Widget
Build the viewport.
inherited
createElement() StatelessElement
Creates a StatelessElement to manage this widget's location in the tree.
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
getDirection(BuildContext context) AxisDirection
Returns the AxisDirection in which the scroll view scrolls.
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}) 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