I'm looking at the async redux example here:
https://github.com/reactjs/redux/blob/master/examples/async/src/containers/App.js
If I add the following:
function mapDispatchToProps(dispatch) {
return {};
}
export default connect(mapStateToProps,mapDispatchToProps)(App)
Then dispatch is no longer defined in componentDidMount. Why is this? How can I access dispatch here while using mapDispatchToProps?
The connect function automatically passes dispatch to your props if you do not specify a mapDispatchToProps function. With that in mind:
export default connect(mapStateToProps)(App)
And it should work. You can read more about the react-redux bindings in the docs.
If I understand you correctly, you want to call dispatch from the componentDidMount as a function in the this.props (which I don't recommend, check how redux works and create the action creators that you need). Even so, to achieve that you can do that:
function mapDispatchToProps(dispatch) {
return { dispatch };
}
That creates a dispatch property that is the dispatch function itself.
Still, don't do that on a real use case and keep reading about redux action.creators.
Following the given example, you pass mapDispatchToProps to connect like this
function mapDispatchToProps(dispatch) {
return {
onClick: nextReddit => {
dispatch(selectReddit(nextReddit));
}
};
}
export default connect(mapStateToProps, mapDispatchToProps)(App)
Component App will then be empowered with a prop onClick which is used as below.
handleChange = nextReddit => {
this.props.onClick(nextReddit)
}
render() {
...
return (
...
<Picker value={selectedReddit}
onChange={this.handleChange}
options={[ 'reactjs', 'frontend' ]} />
...
);
}
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
});
This question already has answers here:
What is mapDispatchToProps?
(6 answers)
Closed 4 years ago.
What's the difference between mapStateToProps and mapDispatchToProps arguments to the connect function in react-redux?
mapStateToProps is a function that you would use to provide the store data to your component, whereas mapDispatchToProps is something that you will use to provide the action creators as props to your component.
According to the docs:
If mapStateToProps argument is specified, the new component will
subscribe to Redux store updates. This means that any time the store
is updated, mapStateToProps will be called. The results of
mapStateToProps must be a plain object, which will be merged into
the component’s props.
With mapDispatchToProps every action creator wrapped into a dispatch
call so they may be invoked directly, will be merged into the
component’s props.
A simple example would be
function mapStateToProps(state) {
return { todos: state.todos }
}
function mapDispatchToProps(dispatch) {
return { addTodo: bindActionCreators(addTodo, dispatch) }
}
export default connect(mapStateToProps, mapDispatchToProps)(Todos);
In a very simple term,
mapStateToProps: It connects redux state to props of react component.
mapDispatchToProps: It connects redux actions to react props.
A really light example: ( I hope, you know what I mean)
// state
const mapStateToProps = state => {
return { lists: state.lists };
};
// props
const mapDispatchToProps = ({ lists }) => (
<ul>
{
lists.map(el => (
<li key={ el.id }>
{ el.heading }
</li>
)
}
</ul>
);
// Now, connect state to prop
const List = connect(mapStateToProps)(mapDispatchToProps);
In very simple terms:
mapStateToProps is called when you want to get the value of the global state from your component
function mapStateToProps(state) {
return {
message: state.message
};
}
The value of the global state is only changed with the help of an action. So if you want to change the value of global state you need an action. mapDispatchToProps is used to bind action in your component.
Below is the Higher order component. The HOC is connected to redux specifically to get access to one of the action creators: importantReduxAction.
function withExtraStuff (InnerComponent) {
return class Enhancer extends React.Component {
constructor(props){
super(props)
this.importantMethod = this.importantMethod.bind(this)
}
importantMethod(){
//try to call the higher order component's action creator
this.props.importantReduxAction()
}
render(){
return <InnerComponent
{...this.props}
importantMethod={this.importantMethod}
/>
}
}
let mapDispatchToProps = (dispatch)=>{
return bindActionCreators({importantReduxAction}, dispatch)
}
return connect(null, mapDispatchToProps, null, {pure: false})(Enhancer)
}
This is the wrapped component that will use the HOC component. It also connects itself to redux in order to gain access to a different method: otherReduxAction.
class ChildComponent extends React.Component {
constructor(props){
super(props)
this.doImportantThing = this.doImportantThing.bind(this)
}
doImportantThing(){
//try to call the higher order component's method (this is where problems occur)
this.props.importantMethod()
//do something with this components dispatch
this.props.otherReduxAction()
}
render(){
return <div>
{this.doImportantThing()}
</div>
}
}
let EnhancedComponent = withExtraStuff(ChildComponent)
let mapDispatchToProps = (dispatch)=>{
return bindActionCreators({otherReduxAction}, dispatch)
}
export default connect(null, mapDispatchToProps, null, {pure: false})(EnhancedComponent)
The problem occurs that my mapDispatchToProps inside of my HOC is being overwritten by the child, and the action creator: importantReduxAction, is never being passed into my HOC. It receives the error that the:
method is undefined
I have solved this by passing the method into my child component like so:
/* CHILD COMPONENT DEFINITION ABOVE */
let mapDispatchToProps = (dispatch)=>{
return bindActionCreators({otherReduxAction, importantReduxAction}, dispatch)
}
But that solution is not really the way that I want things to work. Is there a way to have my HOC merge in the action creators that it wants to use with those of the wrapped component? Or am I going to have to find a new way around this?
TLDR: HOC Component that uses an action creator wraps child component that also has one. HOC action creator gets kicked to curb and never passed.
It looks like you have an issue with your example.
function withExtraStuff (InnerComponent) {
return class Enhancer extends React.Component {/* ... */}
// ...
return connect(/* ... */)(Enhancer)
}
You're returning twice from your HOC, so your Enhancer is never connected.
Is this just a typo in your example? Or do you have this same issue in your code? Because that would indeed cause the issue you're seeing.
The issue here is that you need to merge your props in the higher order component. The redux connect takes a third parameter which is a function (mergeProps). This function takes three parameters. See example here:
function mergeProps(stateProps, dispatchProps, ownProps) {
return {
...stateProps,
...dispatchProps,
...ownProps,
actions: Object.assign({}, dispatchProps.actions, ownProps.actions)
}
}
In my Wrapped Component I set up my mapDispatchToProps like so:
function mapDispatchToProps(dispatch) {
return {
actions: bindActionCreators({
...myDefinedActionsForMyComponent,
}, dispatch)
}
}
And in my HOC I set up my mapDispatchToProps the same way. The issue you are having can be resolved by implementing mergeProps in your HOC (higher order component). If you simply create the mergeProps function and console log the three parameters you'll see the values and can decide how best to join them. Based on my set up I simply had to do an object assign on the actions. You probably need to do something similar.
The connect would then look something like this in your HOC:
return connect(mapStateToProps, mapDispatchToProps, mergeProps)(Wrapper)
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