React/Redux store updating but Component not re-rendering

Question

I have seen a lot of SO/github issues with this title, and I'm sure that actually did not do what causes this error 99% of the time: -connect wrapper component with MapStateToProps and MapDispatchToProps, -return new State instead of mutating actual state in reducer.

In the redux devtools extension, I can see the StoreState changing with the new Todo in the list when I dispatch a ADD_TODO. When I dispatch a ADD_TODO, Body component is not re-rendered. If I inject a Todo in the todos initial StoreState, The Todo is displayed in the Body Component.

You can find the repository here

reducer :

import { TodoAction } from '../actions';
import { StoreState } from '../types/index';
import { ADD_TODO, TOGGLE_TODO } from '../constants/index';
import TodoModel from '../models/TodoModel';

export function todos(state: StoreState, action: TodoAction): StoreState {
    let todos: Array<TodoModel>;
    switch (action.type) {
        case ADD_TODO:
            todos = state.todos;
            todos.unshift(action.todo);
            return { ...state, todos: todos };
        case TOGGLE_TODO:
            todos = state.todos;
            const todo = todos.find(todo => todo.id === action.todo.id);
            if (todo !== undefined) {
                const key = todos.indexOf(todo);
                todos[key].done = true;
            }
            return { ...state, todos: todos };
        default:
            return state;
    }
}

Container component:

export default connect(mapStateToProps, mapDispatchToProps)(Body);
import Body from '../components/Body/Body';
import { StoreState } from '../types/index';
import { connect } from 'react-redux';

export function mapStateToProps({ todos }: StoreState) {
    return {
        todos
    };
}

export function mapDispatchToProps() {
    return {
        //
    };
}
export default connect(mapStateToProps, mapDispatchToProps)(Body);

Component not updated by storeState changes :

import * as React from 'react';
import TodoModel from '../../models/TodoModel';

interface Props {
    todos: Array<TodoModel>;
}

interface State {

}

class Body extends React.Component<Props, State> {

    constructor(props: Props) {
        super(props);
    }

    render() {
        console.log(this.props);
        return (
            <div>
                <ul>
                    {this.props.todos.map(todo => <li key={todo.id}>{todo.content}</li>)}
                </ul>
            </div>
        );
    }
}

export default Body;

Tomasz Mularczyk Tomasz Mularczyk · Accepted Answer · 2018-05-05T09:52:56

unshift mutates the array, you need to return a new one:

case ADD_TODO:
    todos = [...state.todos]; // or - state.todos.slice();
    todos.unshift(action.todo);
    return { ...state, todos: todos };

React/Redux store updating but Component not re-rendering

1 Answers