import 'package:flutter/material.dart';

import 'package:get_it/get_it.dart';

import 'package:provider/provider.dart';

​

class StateFullConsumerWidget<T extends ChangeNotifier> extends StatefulWidget{

​

  StateFullConsumerWidget({@required this.builder,Key key,this.onPostViewModelInit,this.child}) : super(key : key);

​

  final Widget Function(BuildContext context, ChangeNotifier value, Widget child) builder;

  final Widget child;

​

  final void Function(T) onPostViewModelInit;

​

  @override

  _StateFullConsumerWidgetState<T> createState() => _StateFullConsumerWidgetState<T>();

}

​

class _StateFullConsumerWidgetState<T extends ChangeNotifier> extends State<StateFullConsumerWidget>{

  T _viewModel;

  @override

  void initState() {

    // assign the model once when state is initialised

    _viewModel = GetIt.instance.get<T>();

    widget.onPostViewModelInit(_viewModel);

​

​

    super.initState();

  }

  @override

  Widget build(BuildContext context) {

    return ChangeNotifierProvider<T>(

      builder: (context) => _viewModel,

      child: Consumer<T>(

        builder: widget.builder,

        child: widget.child,

      ),

    );

  }

​

}

// example of using generics in Dart

​

class Box<T> {

  T value;

​

  Box(this.value);

​

  T getValue() {

    return value;

  }

​

  void setValue(T newValue) {

    value = newValue;

  }

}

​

void main() {

  // creating an instance of Box with int as the generic type

  Box<int> intBox = Box<int>(10);

  print(intBox.getValue()); // output: 10

​

  // creating an instance of Box with String as the generic type

  Box<String> stringBox = Box<String>("Hello");

  print(stringBox.getValue()); // output: Hello

}