InheritedModel<T> class

An InheritedWidget that's intended to be used as the base class for models whose dependents may only depend on one part or "aspect" of the overall model.

An inherited widget's dependents are unconditionally rebuilt when the inherited widget changes per InheritedWidget.updateShouldNotify. This widget is similar except that dependents aren't rebuilt unconditionally.

Widgets that depend on an InheritedModel qualify their dependence with a value that indicates what "aspect" of the model they depend on. When the model is rebuilt, dependents will also be rebuilt, but only if there was a change in the model that corresponds to the aspect they provided.

The type parameter T is the type of the model aspect objects.

Widgets create a dependency on an InheritedModel with a static method: InheritedModel.inheritFrom. This method's context parameter defines the subtree that will be rebuilt when the model changes. Typically the inheritFrom method is called from a model-specific static of method. For example:

class MyModel extends InheritedModel<String> {
  // ...
  static MyModel of(BuildContext context, String aspect) {
    return InheritedModel.inheritFrom<MyModel>(context, aspect: aspect);
  }
}

Calling MyModel.of(context, 'foo') means that context should only be rebuilt when the foo aspect of MyModel changes. If the aspect is null, then the model supports all aspects.

When the inherited model is rebuilt the updateShouldNotify and updateShouldNotifyDependent methods are used to decide what should be rebuilt. If updateShouldNotify returns true, then the inherited model's updateShouldNotifyDependent method is tested for each dependent and the set of aspect objects it depends on. The updateShouldNotifyDependent method must compare the set of aspect dependencies with the changes in the model itself.

For example:

class ABModel extends InheritedModel<String> {
  ABModel({ this.a, this.b, Widget child }) : super(child: child);

  final int a;
  final int b;

  @override
  bool updateShouldNotify(ABModel old) {
    return a != old.a || b != old.b;
  }

  @override
  bool updateShouldNotifyDependent(ABModel old, Set<String> aspects) {
    return (a != old.a && aspects.contains('a'))
        || (b != old.b && aspects.contains('b'))
  }

  // ...
}

In the previous example the dependencies checked by updateShouldNotifyDependent are just the aspect strings passed to inheritFromWidgetOfExactType. They're represented as a Set because one Widget can depend on more than one aspect of the model. If a widget depends on the model but doesn't specify an aspect, then changes in the model will cause the widget to be rebuilt unconditionally.

Inheritance

Constructors

InheritedModel({Key key, Widget child })
Creates an inherited widget that supports dependencies qualified by "aspects", i.e. a descendant widget can indicate that it should only be rebuilt if a specific aspect of the model changes.
const

Properties

child Widget
The widget 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

createElement() InheritedModelElement<T>
Inflates this configuration to a concrete instance. [...]
override
isSupportedAspect(Object aspect) bool
Returns true if this model supports the given aspect. [...]
@protected
updateShouldNotifyDependent(covariant InheritedModel<T> oldWidget, Set<T> dependencies) bool
Return true if the changes between this model and oldWidget match any of the dependencies.
@protected
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
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
updateShouldNotify(covariant InheritedWidget oldWidget) bool
Whether the framework should notify widgets that inherit from this widget. [...]
@protected, inherited

Operators

operator ==(dynamic other) bool
The equality operator. [...]
inherited

Static Methods

inheritFrom<T extends InheritedModel<Object>>(BuildContext context, { Object aspect }) → T
Makes context dependent on the specified aspect of an InheritedModel of type T. [...]