Access State with useSelector

Learning Goals

Use the react-redux library to connect the Redux store to the React application
Utilize the <Provider /> component and the useSelector hook to access Redux store content

Overview

In this lesson, we want to explore how useSelector is used to connect regular React components with the Redux store. This is also a good opportunity to review the steps for using the redux and react-redux packages in your app.

Instructions

Some files are provided, including UserInput and the reducer in the usersSlice.js file, but the Redux store isn't fully hooked up yet.

Connecting to Redux

In src/index.js, use the createStore method from redux, passing in the provided reducer, usersReducer, to create a store. Use Provider from react-redux to wrap <App />, passing store as a prop to the Provider. This will give your components access to the store.

Test by Dispatching an Action

Run npm start and open up your browser's dev console. If everything is connected correctly in index.js, a form should appear in the browser. Submitting something using the form will cause a console.log to fire in our reducer, indicating that the values have been added to our store.

In UserInput.js, we can see the code that fires when we press the submit button:

// ...

function handleOnSubmit(event) {
  event.preventDefault();
  dispatch({ type: "users/add", payload: formData });
}

return <form onSubmit={handleOnSubmit}>{/* ... */}</form>;

We can see that, on submit, handleOnSubmit() is called. event.preventDefault() is called to stop the page from refreshing, then dispatch() is called with a custom action, {type: 'users/add', payload: formData}.

The dispatch function is provided by calling the useDispatch hook from react-redux in our component.

Using the `useSelector` Hook

Now that we've got a working store, we want to get access to it and display the contents of our store's state.

Import the useSelector hook in Users.js
Call useSelector inside your component, passing in a callback function that accepts one argument, state, the current version of your store's state. Use state to access the array of users and return that from the callback function. Save the return value of calling useSelector to a variable so that you can use the users array in your component.

The Users component should display the username of a user submitted to the store. To pass the final test, it should also display a total count of current users. Try to use useSelector to solve both. You can call useSelector multiple times to return different values: one for users and one for the userCount.

Conclusion

With all tests passing, you should have a working form that adds and successfully displays usernames, as well as a total count of those users. While these are small bits of data, we've got a fully integrated React/Redux application, ready to be expanded upon!

mateo815/react-hooks-redux-use-selector-lab