I'm trying to learn and test React.PureComponent and it keeps rendering even though no state changes for that pure component.
My PureComponent is very simple and it accepts only one Redux Action function via connect hoc
import React from 'react';
import {
Container,
Button
} from 'reactstrap'
import { connect } from 'react-redux'
import { resetWorkouts } from '../actions/workoutApiActions'
class About extends React.PureComponent {
render () {
const { resetWorkouts } = this.props;
console.log('in about render...')
return (
<React.Fragment>
<Container>
<h2>Api Data Reset</h2>
<Button color="danger" onClick={resetWorkouts}>Reset Data</Button>
</Container>
</React.Fragment>
);
}
}
const mapDispatchToProps = dispatch => {
return {
resetWorkouts: () => dispatch(resetWorkouts())
}
}
export default connect(null, mapDispatchToProps)(About);
In the above code, you can see that, there is no state in the component. It only accepts the action function as props from connect. However, whenever I clicks on the Reset Data button, it keeps calling the render method as shown in the screenshot.
In the screenshot, I can see that, global state store has been changed whenever, I click a button. But, that state is not used in my PureComponent and it should be out of the scope and my component should ignore to re-render.
Or Redux Action functions are created every time the global state store has been changed. And passed as a new object to my PureComponent ?
Theoretically, I don't need to write my own shouldComponentUpdate function, right? I'm confused and could you please help me to understand about this behaviour?
My goal is I don't want my PureComponent to render again when a user clicks a button.
Updates:
I have tried like the following according to this article and it's still re-rendering
const mapDispatchToProps = {
resetWorkouts
};
this because react do a shallow comparison between the prevProps and the nextProps,
and you can control that only in the shouldComponentUpdate, react doesn't know that the dispatcher is the same one from the previous render, because you are using return inside the mapDispatchToProps function.
In your component and in your case, while the function will remain the same, you can go with two paths:
path 1:
override the shouldComponentUpdate life cycle hook, to be as the following:
shouldComponentUpdate(){
return false;
}
path 2:
get rid of the return inside mapDispatchToProps and simplify the connect so it be as the following:
`conncect(state => ({}), {
resetWorkouts: resetWorkouts})(YourComponent);`
using one of the above paths should make you good to go
The reason why your component is rendering is because everytime the following function executes:
const mapDispatchToProps = dispatch => {
return {
resetWorkouts: () => dispatch(resetWorkouts())
}
}
your components receives a new instance of a property named resetWorkouts(because you're creating an inline array function). You may look at the ownProps to check if your component already have the resetWorkouts:
const mapDispatchToProps = (dispatch, ownProps) => {
return {
resetWorkouts: ownProps.resetWorkouts || () => dispatch(resetWorkouts())
}
}
Related
I've an application when most of the data are stored in the store but the selected item is provided thought the usage of a React.Context.
React-Redux provide the connect api that accept a mapStateToProps function with state and props as a component.
What I would like, if it didn't break the hooks, is something like:
function mapStateToProps(state){
const selectedItemId = useContext(MySelectedItemContext)
return {
item: state.items[selectedItemId]
}
}
but of course it is not possible since I'm outside of the component and cannot invoke the useContext.
So, I tried to use the old API context:
function mapStateToProps(state, props){
return {
item: state.items[props.id]
}
}
export default connect(mapStateToProps)((props) =>
<MySelectedItemContext.Consumer>
{ selectedItemId => <Component id={selectedItemId} {...props}/> }
</MySelectedItemContext.Consumer>)
but this still not works because the connect returns a new component that has the consumer inside instead of outside and id prop is not defined yet in mapStateToProps.
Any idea?
The best way is to remove mapStateToProps and use useSelector hooks and Redux selectors. But if you need mapStateToProps, then you can wrap your component that must be connected to Redux into another component that will get value from context and will pass it to a component that uses Redux.
// Use this component
export function ContextConsumerComponent() {
const selectedItemId = useContext(SelectedItemIdContext);
return <ReduxConsumerComponent id={selectedItemId} />;
}
function mapStateToProps(state, props) {
return {
item: state.items[props.id]
}
}
const ReduxConsumerComponent = connect(mapStateToProps)((props) => {
// props.item will be here
});
I'm dealing with a mix of function components and class components. Every time a click happens in the NavBar I want to trigger the function to validate the Form, it has 5 forms, so each time I'm going to have to set a new function inside the context API.
Context.js
import React, { createContext, useContext, useState } from "react";
const NavigationContext = createContext({});
const NavigationProvider = ({ children }) => {
const [valid, setValid] = useState(false);
const [checkForm, setCheckForm] = useState(null);
return (
<NavigationContext.Provider value={{ valid, setValid, checkForm, setCheckForm }}>
{children}
</NavigationContext.Provider>
);
};
const useNavigation = () => {
const context = useContext(NavigationContext);
if (!context) {
throw new Error("useNavigation must be used within a NavigationProvider");
}
return context;
};
export { NavigationProvider, useNavigation, NavigationContext};
Form.js
import React, { Component } from "react";
import { NavigationContext } from "../hooks/context";
class Something extends Component {
static contextType = NavigationContext;
onClickNext = () => {
// This is the funcion I want to set inside the Context API
if(true){
return true
}
return false;
};
render() {
const { setCheckForm } = this.context;
setCheckForm(() => () => console.log("Work FFS"));
return (
<>
<Button
onClick={this.onClickNext}
/>
</>
);
}
}
export default Something;
The problem when setting the function it throws this error:
Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops.
And setting like setCheckForm(() => console.log("Work FFS"));, it triggers when rendered.
Render method of React.Component runs whenever state changes and setCheckForm updates the state whenever that render happens. This creates an infinite loop, this is the issue you are having there.
So, this is a lifecycle effect, you have to use that function inside componentDidMount if you want to set it when the component first loads.
While this solves your problem, I wouldn't suggest doing something like this. React's mental model is top to bottom, data flows from parent to child. So, in this case, you should know which component you are rendering from the parent component, and if you know which component to render, that means you already know that function which component is going to provide to you. So, while it is possible in your way, I don't think it is a correct and Reactish way to handle it; and it is probably prone to break.
I'm trying to understand React Hooks. What I want is to fetch data inside functional component by call redux action with useEffect hooks.
I know that I can pass props to state like
const [todoList] = useState(props.todoList)
But what is the best practice to fetch data by existing redux actions?
In React class component i call this method to fetch data in componentDidMount() and everythink works.
import React, { useEffect } from 'react'
import { connect } from 'react-redux'
import { ITodo } from './types'
import { getTodos } from '../actions/todoActions'
interface IProps {
todoList: Array<ITodo>
getTodos: typeof getTodos
}
const Todos = (props: IProps) => {
useEffect(() => {
props.getTodos()
}, [props.todoList])
return (
<div>
{props.todoList.map((_) => (<div key={_.Id}>{_.Name}</div>))}
</div>
)
}
const mapStateToProps = (state) => ({
todoList: state.todo.todoList
})
const mapDispatchToProps = {
getTodos
}
export default connect(mapStateToProps, mapDispatchToProps)(ProdRoute)
I expected to get list of todos with props and props.getTodos() should call once like in componentDidMount() method. But actualy I get data and getTodos() are called over and over again but should be called once on component mount
Take care that if you pass [props.todoList] to the useEffect you are erroneously forcing a constant refresh because:
useEffect does an instance comparison (===) to know if props.todoList is changed
after the the very first render the props.getTodos() dispatcher is called
when the props.todoList will be updated the component is re-rendered
the useEffect call will receive [props.todoList] as a value to check if it needs to re-run or not
props.todoList is changed (it was empty and now it's valorized) and props.getTodos() is so re-called
redux updates the todoList with the same values but mutating the array reference
the component is re-rendered and the useEffect will check if the [props.todoList] param is been updated... but IT IS BEEN UPDATED because the previous props.todoList is different from the actual props.todoList, even if the content is the same
So, if you need to call the props.getTodos() just once can
use [props.todoList.length] instead of [props.todoList] as the second parameter for the useEffect call
use an empty array [] as the second parameter for the useEffect call (see the docs)
I'm new to Redux and I have this question that I can't solve by myself.
I created a TODO list app and now I need to add a new task to the list. The user writes something in a text input and when he clicks the button the new task must be appended to the list.
I already get a 'ADD TASK' action. But I don't know how to call it from inside a component method. So I added an event listener to the button, but when I click it what should I do next?
class List extends React.Component{
addTask(e){
var title = $('[name=title]');
title.val('');
//what should I do?
}
render(){
const mappedTasks = this.props.tasks.map(function(task){
return (
<li key={task.title}>{task.title}</li>
);
});
return (
<div>
<ul>
{mappedTasks}
</ul>
<input name='title' />
<button onClick={this.addTask}>Adicionar</button>
</div>
);
};
}
const mapStateToProps = function(state,ownProps){
return {
message: 'Hello World!',
tasks: state.tasks
}
}
const ListComponent = connect(
mapStateToProps
)(List);
In this example I want to dispatch something from the addTask method.
So what is the proper way of dispatching from a Component method on Redux?
#edit this did the trick:
In render function
<button onClick={this.addTask.bind(this)}>Adicionar</button>
So as Brandon said I could use in the method
this.props.dispatch({type:'ADD_TASK', payload: {title: title.value}});
I see a couple of possible solutions, and which one is more appropriate might depend on your particular use case. There are a few questions that might help:
Is this List component connect-ed to the redux store (using the connect() decorator from the react-redux package? If so, you
should be able to dispatch an action as simply as this:
this.props.dispatch(someActionCreator()).
Are you open to connect-ing this component to the store? If so, decorate the List component like so: connect(mapStateToProps, mapDispatchToProps)(List). Then you'll have access to dispatch() on props in the List component and can proceed just as in question 1.
Does the List component have an ancestor with access to the dispatch() function. If so, you can create an action dispatching function at that level and pass it down as a prop until you reach the List component, where you can call that function.
As I said, your particular use case will determine the suitability of each approach. If you have any more questions, I'm happy to help, so let me know.
Can use something like this.
import { Component } from 'react'
import { bindActionCreators } from 'redux'
import { connect } from 'react-redux'
import * as TodoActionCreators from './TodoActionCreators'
console.log(TodoActionCreators)
// {
// addTodo: Function,
// removeTodo: Function
// }
class TodoListContainer extends Component {
componentDidMount() {
// Injected by react-redux:
let { dispatch } = this.props
// Note: this won't work:
// TodoActionCreators.addTodo('Use Redux')
// You're just calling a function that creates an action.
// You must dispatch the action, too!
// This will work:
let action = TodoActionCreators.addTodo('Use Redux')
dispatch(action)
}
render() {
// Injected by react-redux:
let { todos, dispatch } = this.props
// Here's a good use case for bindActionCreators:
// You want a child component to be completely unaware of Redux.
let boundActionCreators = bindActionCreators(TodoActionCreators, dispatch)
console.log(boundActionCreators)
// {
// addTodo: Function,
// removeTodo: Function
// }
return (
<TodoList todos={todos}
{...boundActionCreators} />
)
// An alternative to bindActionCreators is to pass
// just the dispatch function down, but then your child component
// needs to import action creators and know about them.
// return <TodoList todos={todos} dispatch={dispatch} />
}
}
export default connect(
state => ({ todos: state.todos })
)(TodoListContainer)
One most common way to dispatch an action in component is to dispose the action to props using mapDispatchToProps. Then you can dispatch an action from props.
componentWillMount() {
this.props.actions.loadPropImages();
}
function mapDispatchToProps(dispatch) {
return {
actions: bindActionCreators(imageActions, dispatch)
};
}
export default connect(mapStateToProps, mapDispatchToProps)(EditorPage);
I was reading the documentation for the Redux library and it has this example:
In addition to reading the state, container components can dispatch actions. In a similar fashion, you can define a function called mapDispatchToProps() that receives the dispatch() method and returns callback props that you want to inject into the presentational component.
This actually makes no sense. Why do you need mapDispatchToProps when you already have mapStateToProps?
They also provide this handy code sample:
const mapDispatchToProps = (dispatch) => {
return {
onTodoClick: (id) => {
dispatch(toggleTodo(id))
}
}
}
What is this function and why it is useful?
I feel like none of the answers have crystallized why mapDispatchToProps is useful.
This can really only be answered in the context of the container-component pattern, which I found best understood by first reading:Container Components then Usage with React.
In a nutshell, your components are supposed to be concerned only with displaying stuff. The only place they are supposed to get information from is their props.
Separated from "displaying stuff" (components) is:
how you get the stuff to display,
and how you handle events.
That is what containers are for.
Therefore, a "well designed" component in the pattern look like this:
class FancyAlerter extends Component {
sendAlert = () => {
this.props.sendTheAlert()
}
render() {
<div>
<h1>Today's Fancy Alert is {this.props.fancyInfo}</h1>
<Button onClick={sendAlert}/>
</div>
}
}
See how this component gets the info it displays from props (which came from the redux store via mapStateToProps) and it also gets its action function from its props: sendTheAlert().
That's where mapDispatchToProps comes in: in the corresponding container
// FancyButtonContainer.js
function mapDispatchToProps(dispatch) {
return({
sendTheAlert: () => {dispatch(ALERT_ACTION)}
})
}
function mapStateToProps(state) {
return({fancyInfo: "Fancy this:" + state.currentFunnyString})
}
export const FancyButtonContainer = connect(
mapStateToProps, mapDispatchToProps)(
FancyAlerter
)
I wonder if you can see, now that it's the container 1 that knows about redux and dispatch and store and state and ... stuff.
The component in the pattern, FancyAlerter, which does the rendering doesn't need to know about any of that stuff: it gets its method to call at onClick of the button, via its props.
And ... mapDispatchToProps was the useful means that redux provides to let the container easily pass that function into the wrapped component on its props.
All this looks very like the todo example in docs, and another answer here, but I have tried to cast it in the light of the pattern to emphasize why.
(Note: you can't use mapStateToProps for the same purpose as mapDispatchToProps for the basic reason that you don't have access to dispatch inside mapStateToProp. So you couldn't use mapStateToProps to give the wrapped component a method that uses dispatch.
I don't know why they chose to break it into two mapping functions - it might have been tidier to have mapToProps(state, dispatch, props) IE one function to do both!
1 Note that I deliberately explicitly named the container FancyButtonContainer, to highlight that it is a "thing" - the identity (and hence existence!) of the container as "a thing" is sometimes lost in the shorthand
export default connect(...)
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
syntax that is shown in most examples
It's basically a shorthand. So instead of having to write:
this.props.dispatch(toggleTodo(id));
You would use mapDispatchToProps as shown in your example code, and then elsewhere write:
this.props.onTodoClick(id);
or more likely in this case, you'd have that as the event handler:
<MyComponent onClick={this.props.onTodoClick} />
There's a helpful video by Dan Abramov on this here:
Redux: Generating Containers with connect() from React Redux (VisibleTodoList)
mapStateToProps() is a utility which helps your component get updated state(which is updated by some other components),
mapDispatchToProps() is a utility which will help your component to fire an action event (dispatching action which may cause change of application state)
mapStateToProps, mapDispatchToProps and connect from react-redux library provides a convenient way to access your state and dispatch function of your store. So basically connect is a higher order component, you can also think as a wrapper if this make sense for you. So every time your state is changed mapStateToProps will be called with your new state and subsequently as you props update component will run render function to render your component in browser. mapDispatchToProps also stores key-values on the props of your component, usually they take a form of a function. In such way you can trigger state change from your component onClick, onChange events.
From docs:
const TodoListComponent = ({ todos, onTodoClick }) => (
<ul>
{todos.map(todo =>
<Todo
key={todo.id}
{...todo}
onClick={() => onTodoClick(todo.id)}
/>
)}
</ul>
)
const mapStateToProps = (state) => {
return {
todos: getVisibleTodos(state.todos, state.visibilityFilter)
}
}
const mapDispatchToProps = (dispatch) => {
return {
onTodoClick: (id) => {
dispatch(toggleTodo(id))
}
}
}
function toggleTodo(index) {
return { type: TOGGLE_TODO, index }
}
const TodoList = connect(
mapStateToProps,
mapDispatchToProps
)(TodoList)
Also make sure that you are familiar with React stateless functions and Higher-Order Components
Now suppose there is an action for redux as:
export function addTodo(text) {
return {
type: ADD_TODO,
text
}
}
When you do import it,
import {addTodo} from './actions';
class Greeting extends React.Component {
handleOnClick = () => {
this.props.onTodoClick(); // This prop acts as key to callback prop for mapDispatchToProps
}
render() {
return <button onClick={this.handleOnClick}>Hello Redux</button>;
}
}
const mapDispatchToProps = dispatch => {
return {
onTodoClick: () => { // handles onTodoClick prop's call here
dispatch(addTodo())
}
}
}
export default connect(
null,
mapDispatchToProps
)(Greeting);
As function name says mapDispatchToProps(), map dispatch action to props(our component's props)
So prop onTodoClick is a key to mapDispatchToProps function which delegates furthere to dispatch action addTodo.
Also if you want to trim the code and bypass manual implementation, then you can do this,
import {addTodo} from './actions';
class Greeting extends React.Component {
handleOnClick = () => {
this.props.addTodo();
}
render() {
return <button onClick={this.handleOnClick}>Hello Redux</button>;
}
}
export default connect(
null,
{addTodo}
)(Greeting);
Which exactly means
const mapDispatchToProps = dispatch => {
return {
addTodo: () => {
dispatch(addTodo())
}
}
}
mapStateToProps receives the state and props and allows you to extract props from the state to pass to the component.
mapDispatchToProps receives dispatch and props and is meant for you to bind action creators to dispatch so when you execute the resulting function the action gets dispatched.
I find this only saves you from having to do dispatch(actionCreator()) within your component thus making it a bit easier to read.
React redux: connect: Arguments