scoped_model
A set of utilities that allow you to easily pass a data Model from a parent Widget down to its descendants. In addition, it also rebuilds all of the children that use the model when the model is updated. This library was originally extracted from the Fuchsia codebase.
This Library provides three main classes:
- The
Modelclass. You will extend this class to create your own Models, such asSearchModelorUserModel. You can listen to Models for changes! - The
ScopedModelWidget. If you need to pass aModeldeep down your Widget hierarchy, you can wrap yourModelin aScopedModelWidget. This will make the Model available to all descendant Widgets. - The
ScopedModelDescendantWidget. Use this Widget to find the appropriateScopedModelin the Widget tree. It will automatically rebuild whenever the Model notifies that change has taken place.
This library is built upon several features of Flutter:
- The
Modelclass implements theListenableinterfaceAnimationControllerandTextEditingControllerare alsoListenables
- The
Modelis passed down the Widget tree using anInheritedWidget. When anInheritedWidgetis rebuilt, it will surgically rebuild all of the Widgets that depend on its data. No need to manage subscriptions! - It uses the
AnimatedBuilderWidget under the hood to listen to the Model and rebuild theInheritedWidgetwhen the model changes.
Examples
- Counter App - Introduction to the tools provided by Scoped Model.
- Todo App - Shows how to write a Todo app with persistence and tests.
Usage
Let's demo the basic usage with the all-time favorite: A counter example!
// Start by creating a class that holds some view the app's state. In
// our example, we'll have a simple counter that starts at 0 can be
// incremented.
//
// Note: It must extend from Model.
class CounterModel extends Model {
int _counter = 0;
int get counter => _counter;
void increment() {
// First, increment the counter
_counter++;
// Then notify all the listeners.
notifyListeners();
}
}
// Create our App, which will provide the `CounterModel` to
// all children that require it!
class CounterApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
// First, create a `ScopedModel` widget. This will provide
// the `model` to the children that request it.
return new ScopedModel<CounterModel>(
model: new CounterModel(),
child: new Column(children: [
// Create a ScopedModelDescendant. This widget will get the
// CounterModel from the nearest ScopedModel<CounterModel>.
// It will hand that model to our builder method, and rebuild
// any time the CounterModel changes (i.e. after we
// `notifyListeners` in the Model).
new ScopedModelDescendant<CounterModel>(
builder: (context, child, model) => new Text('${model.counter}'),
),
new Text("Another widget that doesn't depend on the CounterModel")
])
);
}
}
Finding the Model
There are two ways to find the Model provided by the ScopedModel Widget.
- Use the
ScopedModelDescendantWidget. It will find theModeland run the
builder function whenever theModelnotifies the listeners. - Use the
ScopedModel.ofstatic method directly. To make this method more readable for frequent access, you can consider adding your ownofmethod to your ownModelclasses like so:
class CounterModel extends Model {
// ...
/// Wraps [ScopedModel.of] for this [Model].
static CounterModel of(BuildContext context) =>
ScopedModel.of<CounterModel>(context);
}
Listening to multiple Models in a build function
In many cases, it makes sense to split your Models apart into logical components
by functionality. For example, rather than having an AppModel that contains
all of your application logic, it can often make more sense to split models
apart into a UserModel, a SearchModel and a ProductModel, for example.
However, if you need to display information from two of these models in a single
Widget, you might be wondering how to achieve that! To do so, you have two
options:
- Use multiple
ScopedModelDescendantWidgets - Use multiple
ScopedModel.ofcalls. No need to manage subscriptions,
Flutter takes care of all of that through the magic of InheritedWidgets.
class CombinedWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
final username =
ScopedModel.of<UserModel>(context, rebuildOnChange: true).username;
final counter =
ScopedModel.of<CounterModel>(context, rebuildOnChange: true).counter;
return Text('$username tapped the button $counter times');
}
}
Contributors
- Original Fuchsia Authors
- Andrew Wilson
- Brian Egan
- Pascal Welsch