WidgetDriver class abstract

The WidgetDriver is the thing which drives your widget.

This is where you put all of your business logic that is specific to a given widget. You can think of the WidgetDriver as the ViewModel for the widget.

Each Driver is unique to a given widget. You do not share/reuse Drivers between many widgets. Instead each widget has its own Driver.

The Driver provides all dynamic data to the widget via public properties. If these properties depend on some external dependency, then these dependencies are resolved inside the Driver and not in the widget.

E.g. if a text in a widget depends on wether the user is logged in or not, then that AuthService is not resolved in the widget. But instead the Driver resolves it and listens to changes on it. And as soon as a change occurs, then the Driver will call its notifyWidget() method which will trigger the widget to update.

One more benefit which the WidgetDriver gives you is easier/better widget testing. Usually when you test your widgets, then you need to provide mocked values to any dependency which any of your child widgets have. This really clutters your widget test code since most of the code will end up being to define mocks. It also creates tight coupling since any change you make in a child widget might end up breaking all your parent widget tests.

Here the WidgetDriver comes with a solution. If your widget is running in a test environment, then the Driver will not create its "real" instance. Instead it will create a hard coded version of its self called a TestDriver. This TestDriver has no dependencies. It just contains hard coded default values.

Here is a mini example of how to use the WidgetDriver:

class RandomNumberWidgetDriver extends WidgetDriver {
    RandomNumberService _randomNumberService = ...;
    Localization _localization = ...;

    @TestDriverDefaultValue('123')
    int get randomNumber => _randomNumberService.theRandomNumber;

    @TestDriverDefaultValue('Get new random number')
    String get buttonText => _localization.getRandomNumberButtonText;

    @TestDriverDefaultValue()
    void updateRandomNumber() {
        _randomNumberService.generateNewRandomNumber();
        notifyWidget();
    }
}

class RandomNumberWidget extends DrivableWidget<RandomNumberWidgetDriver, RandomNumberWidgetDriverProvider> {
    @override
    Widget build(BuildContext context) {
        return Column(children: [
            Text('${driver.randomNumber}'),
            ElevatedButton(
                child: Text(driver.buttonText),
                onPressed: driver.updateRandomNumber,
            ),
        ]);
    }
    ...
}