Simple MVVM • Documentation • Sample Apps • Pub.dev

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A bold and balanced state management library that pairs MVVM structures with the simplicity of InheritedWidget 🐦🍹

Overview

The Simple MVVM library provides a simple set of widgets to help you pass state data to a subtree.

1. ViewModel - A State object that introduces an InheritedWidget to the widget tree.
2. ViewModelBuilder - A StatefulWidget that you will include in your widget
3. ViewModelProvider - (Behind the scenes) An InheritedWidget that provides the ViewModel to its children

When building with simple_mvvm, you only need to worry about the ViewModel and ViewModelBuilder. The ViewModelProvider is created for you.

The benefit to this approach is that all children within the subtree can access the ViewModel - that's just how InheritedWidgets work.

Depending on your app's needs, you can place a ViewModelBuilder as high up in your app's widget tree as you'd like, making this a convenient way to pass services, constants, etc to your entire application.

Benefits

💙 Pure Flutter

ViewModelProviders are InheritedWidgets, meaning you can access them the using methods built into the Flutter framework. Since the ViewModel is a property on the ViewModelProvider, you can access it using the dependOnInheritedWidgetOfExactType context method. This package sets that up for you so can just do this:

HomeViewModel model = HomeViewModel().of(context);

🍋 Easy Model Usage

The ViewModelProvider provides your model to its children through its builder property so most of the time you won't need to add code to access the model.

return Scaffold(
body: HomeViewModelBuilder(
builder: (context, model) {
return ... // Use the model to render your UI
},
)
);

🔥 No Bloat

This entire library is 60 lines of dart code with no external dependencies.

Setup

Step 1:

Create a ViewModel. The ViewModel is a State object that introduces an InheritedWidget to the widget tree. This is where your business logic will live.

class HomeViewModel extends ViewModel<HomeViewModel> {

  // For convenience, you can add a static .of_ getter. This is optional
  static HomeViewModel of_(BuildContext context) => getModel<HomeViewModel>(context);

  // Here is where you will add your business logic and state properties
  // Notice that you have access to setState here
  ValueNotifier<int> counter = ValueNotifier(0);

  void incrementCounter() {
    setState(() {
      counter.value++;
    });
  }
}

Step 2:

Create a ViewModelBuilder. The ViewModelBuilder is a StatefulWidget that you will include in your widget tree. ViewModelBuilder creates the ViewModel from above.

 class HomeViewModelBuilder extends ViewModelBuilder<HomeViewModel> {
  const HomeViewModelBuilder({
    super.key,
    required super.builder,
  });

  // Override createState to create the specific ViewModel from above
  @override
  State<StatefulWidget> createState() => HomeViewModel();
}

Usage

Once you have your ViewModel and ViewModelBuilder, add the ViewModelBuilder to your widget tree:

return Scaffold(
body: HomeViewModelBuilder(
builder: (context, model) {
return Text('Test')
},
)
);

Now you have several ways to access the ViewModel.

1. Use the provided "model" object:

return Scaffold(
body: HomeViewModelBuilder(
builder: (context, model) {
return Text(model.title); // Add a title String to your ViewModel
},
)
);

2. Use the getModel<T> helper function:

Under the hood, the getModel function uses dependOnInheritedWidgetOfExactType to get the type you specify in the generic parameter T.

return Scaffold(
body: HomeViewModelBuilder(
builder: (context, model) {
return Text(getModel<HomeViewModel>(context).title); // Add a title String to your ViewModel
},
)
,
);

3. Use the ModelWidget:

ModelWidget<ScreenTwoViewModel>
(
builder: (context, model) {
return Text(model.counter.value.toString());
},
)
,

4. Use the .of(context) method:

Each ViewModel has a built in .of() method. This is useful if you break your widget tree up and need to access the model in a different widget:

return Scaffold(
body: HomeViewModelBuilder(
builder: (context, model) {
return Text(HomeViewModel().of(context).title); // Add a title String to your ViewModel
},
)
,
);

The .of(context) method only works on an instance of your ViewModel since static members can't reference type parameters of a class. If you want to save yourself the time it takes to type the extra parenthesis, add a separate method directly in your View Model (classes can't have instance and static methods with the same name, hence the ".of_" vs ".of"):

class HomeViewModel extends ViewModel<HomeViewModel> {

  // Add this
  static HomeViewModel of_(BuildContext context) => getModel<HomeViewModel>(context);
}

To update your UI after a change in the ViewModel, you have two options.

1. Call setState to rebuild the entire widget tree inside your ViewModelBuilder
2. Use a combination of ValueNotifiers and ValueListenableBuilders to selectively rebuild parts of the UI

You can see examples of each of these approaches in the example directory.

Advanced Usage

Initialize and Dispose

Since the ViewModel object extends the State class, you can simply override initState and dispose to run code when the ViewModel is added and removed from the widget tree, respectively:

class HomeViewModel extends ViewModel<HomeViewModel> {

  @override
  void initState() {
    debugPrint('Initialize');
    super.initState();
  }

  @override
  void dispose() {
    debugPrint('Dispose');
    super.dispose();
  }
}

Set Loading

ViewModels include a single ValueNotifier that can be used to mark it as "loading":

ValueNotifier<bool> loading = ValueNotifier(false);

bool get isLoading => loading.value;

void setLoading(bool val) {
  setState(() {
    loading.value = val;
  });
}

For example, you can call model.setLoading(true) when the ViewModel needs to load asynchronous data. When the data is loaded, call model.setLoading(false). In your UI, you can show a spinner if the loading value is true using the model directly. Whenever the loading value is changed, the entire UI inside the ViewModelBuilder will be rebuilt.

class HomeView extends StatelessWidget {
  const HomeView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return HomeViewModelBuilder(
      builder: (context, model) {
        return Scaffold(
          appBar: AppBar(title: Text(model.title)),
          body: Stack(
            children: [
              Text('Hello World!')
              if (model.isLoading) const ColoredBox(color: Colors.black12, child: Center(child: CircularProgressIndicator()))
            ],
          ),
        );
      },
    );
  }
}

Simple MVVM CLI

Check out the cotr_cli.

IntelliJ Live Templates

View

import 'package:simple_mvvm/simple_mvvm.dart';
import 'package:flutter/material.dart';
import '$snakeName$_model.dart';

class $Name$View extends StatelessWidget {
  const $Name$View({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: $Name$ViewModelBuilder(
        builder: (context, model) {
          return Center(child: Text('$Name$'););
        },
      ),
    );
  }
}

ViewModel and ViewModelBuilder

import 'package:simple_mvvm/simple_mvvm.dart';
import 'package:flutter/material.dart';

class $Name$ViewModelBuilder extends ViewModelBuilder<$Name$ViewModel> {
  const $Name$ViewModelBuilder({
    super.key,
    required super.builder,
  });

  @override
  State<StatefulWidget> createState() => $Name$ViewModel();
}

class $Name$ViewModel extends ViewModel<$Name$ViewModel> {
  static $Name$ViewModel of_(BuildContext context) => getModel<$Name$ViewModel>(context);
}

You can read more about using variables in Live Templates here.