dani-mp/ReactNavigation4+Context.js

## ReactNavigation4+Context.js
// So we have a context...

const Context = React.createContext();

class Provider extends React.Component {
  addTodo = todo => this.setState(({ todos }) => ({ todos: [...todos, todo] }));

  state = {
    todos: [],
    addTodo: this.addTodo
  };

  render() {
    return (
      <Context.Provider value={this.state}>
        {this.props.children}
      </Context.Provider>
  }
}

const Consumer = Context.Consumer;

// ... and we have a stack navigator

const Todos = ({ navigation }) => (
  <Consumer>
    {({ todos }) => (<TodosList todos={todos} onAddTodo={navigation.push('AddTodo')} />)}
  </Consumer>
);

const AddTodo = ({ navigation }) => (
  <Consumer>
    {({ addTodo }) => (<CreateTodo onCreateTodo={todo => {
                                                   addTodo(todo);
                                                   navigation.pop();
                                                 }}
                       />)}
  </Consumer>
);

const Stack = createStackNavigator({ Todos, AddTodo });

// you can wrap the stack with the provider...

const StackWithTodos = props => (
  <Provider>
    <Stack {...props} /> // Important: pass down navigation and screenProps from parent for nested navigators.
  </Provider>
);

StackWithTodos.router = Stack.router; // Also important: static router must be the same as well.

// ... and use it wherever you want, without creating a new app container.

const TabNavigator = createBottomTabNavigator({
  TabA: StackWithTodos,
  TabB: ...,
});