ReactJS: Updating parent application state from child component - javascript

Currently trying to learn React by making a simple application that grabs data from the openFEC API.
I currently have two components defined in my application, a SearchBar and a Candidate component. This is what my App.js currently looks like:
class App extends Component {
constructor(props){
super(props);
this.state = { candidate: [], searchTerm: '' }
}
render() {
return (
<div className="App">
<SearchBar />
<Candidate candidate={this.state.candidate}/>
</div>
);
}
}
export default App;
Problem: I need to update the Candidate component based on the data I receive from the API response. However, I'm making the API call in the SearchBar component and have no way of updating the candidate state defined in the App component.
Should I make the API call in the App component instead? If not, is there a way to send the data I get back from the SearchBar component into my App component?

I think the best way to do this is have the API call in your App Component, and pass that function down as a prop to your SearchBar Component. Your parent component (in this case, App) should be holding on to all of the relevant information and passing down to it's children what they need.
It should look something like this:
class App extends Component {
...
handleSearch(term) {
//handle fetch here
.then(res => this.setState({candidate: res})
}
render() {
<div className="App">
<SearchBar handleSearch={this.handleSearch}/>
<Candidate candidate={this.state.candidate}/>
</div>
}
}

In this way, you can achieve this
class App extends Component {
constructor(props){
super(props);
this.state = { candidate: [], searchTerm: '' }
this.triggerSearch=this.triggerSearch.bind(this);
}
triggerSearch(searchTerm){
this.setState({searchTerm})
}
render() {
return (
<div className="App">
<SearchBar trigerSearch=
{(searchTerm)=>this.triggerSearch(searchTerm)} />
<Candidate candidate={this.state.candidate}/>
</div>
);
}
}
export default App;

You can achieve it this way (without making API call from App).
class App extends Component {
constructor(props){
super(props);
this.state = { candidate: [], searchTerm: '' }
this.onDataReceived = this.onDataReceived.bind(this);
}
onDataReceived(data){
this.setState({ candidate: data });
}
render() {
return (
<div className="App">
<SearchBar onDataReceived={this.onDataReceived}/>
<Candidate candidate={this.state.candidate}/>
</div>
);
}
}
Roughly what happens here is:
You can see how I passed a function as a props to the SearchBar component via onDataReceived props.
You can invoke that function from within SearchBar component (e.g. make API call and call function passed as props with API results).
Invoking onDataReceived function will trigger setState
Calling setState will call render and now the Candidate component will receive more recent data from state.
More.

Related

passing state value to a child component via props

i'm trying to pass the value entered by the user from the app component to the passTicket component. I tried invoking props to pass this state data but I keep getting an undefined error when attempting to access it. I'm new to react and it would be great if someone can help me make sense of what i'm getting wrong. This is a sample of what i'm trying to achieve.
This is my main component:
class App extends Component {
constructor(props){
super(props);
this.state = {
ticket:"",
};
this.changeTicket = this.changeTicket.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
this.keyPress = this.keyPress.bind(this);
}
changeTicket(e){
this.setState({
ticket : e.target.value,
})
}
handleSubmit(){
this.setState({
updatedTicket: this.state.ticket
});
}
keyPress(e){
if (e.keyCode ===13){
this.handleSubmit();
}
}
render() {
return (
<div className="App">
<header className="App-header">
<input type="text" placeholder="ENTER TICKET NUMBER" value={this.state.ticket} onKeyDown={this.keyPress} onChange={this.changeTicket}/>
</header>
</div>
);
}
}
and i'd like to be able to store the updatedTicket value in a variable which I can use in my PassTicket component. this is what i've attempted so far but the error it occurs is the following Uncaught TypeError: Cannot read property 'updatedTicket' of undefined
this is what my second component looks like:
class PassTicket extends Component {
transferredTicket(){
const myTicket = this.props.state.updatedTicket;
return myTicket
}
render() {
return (
<p>{this.transferredTicket()}</p>
);
}
}
When passing down a property from a parent to a child component, the property will be stored onto the props by the name it's passed through. For example:
class Parent extends Component {
state = {
ticket: '',
}
render() {
return <ChildComponent updatedTicket={this.state.ticket} />
}
}
class ChildComponent extends Component {
static propTypes = {
updatedTicket: PropTypes.string,
}
static defaultProps = {
updatedTicket: '',
}
render() {
return (
<div>{this.props.updatedTicket}</div>
);
}
}
In the example you've given, it doesn't seem like you're passing the state down to the component you're trying to access it in. In addition, it seems like you're trying to access the updatedTicket as a property of a state object, so just beware of how you're accessing your props.
Therefore, in order to access the updatedTicket property on the child component, you'll first need to import the PassTicket component, instantiate it in the parent (App) component, and pass the property down:
<PassTicket updateTicket={this.state.ticket} />
You would then be able to access the string in the PassTicket component like so - this.props.updateTicket
So .state in react is a local state that is only visible to the individual component. You can read more about it here: https://reactjs.org/docs/state-and-lifecycle.html
In order to pass your state around, you need to use the props system. So where you instantiate your component, you can pass in the state of the parent. For example:
<PassTicket ticket={this.state.updatedTicket}/>
Then inside your PassTicket render function, you can access the ticket prop:
render() {
const { ticket } = this.props
return (
<div>{ticket}</div>
)
}

React - Passing props to App.js

Recently I learned how to pass props from one component to another. In my case, from <FileTree> to <TextBox>, as you can see here: https://codesandbox.io/s/y018010qk9
But after, I reorganized the code a bit and now it is possible to see the structure of my React App inside <App> (App.js). I decided to put the <FileTree> and <TextBox> side by side, with Bootstrap.
So, logically I thought that passing props from <App> to <TextBox> would be the same as I did before: From <FileTree> to <TextBox>. Unfortunatelly, it is not the case.
At the moment, this is the code inside <App>:
// Structure of the project
export class App extends React.Component {
constructor(props) {
super(props);
}
render() {
return (
<div>
<div className="col-md-12">
<SearchEngine />
</div>
<div className="col-md-6">
<FileTree />
</div>
<div className="col-md-6">
<TextBox content={this.props.activeNode} />
</div>
</div>
);
}
}
And here, the code inside <TextBox>:
// TextBox component
export class TextBox extends React.Component {
constructor(props) {
super(props);
this.state = {
content: 'Select A Node To See Its Data Structure Here...'
}
this.showContent = this.showContent.bind(this);
}
showContent (newContent) {
this.setState ({
content: newContent
})
}
componentWillReceiveProps (nextProps) {
this.setState ({
content: nextProps.content
})
}
render() {
return (
<div className="padd_top">
<div className="content_box">{this.state.content}</div>
</div>
);
}
}
export default TextBox;
Just in case, here one can find the <FileTree> component:
// Construction of FileTree
export class FileTree extends React.Component {
constructor(props) {
super(props)
this.state = {
activeNode: null
}
this.setActiveNode = this.setActiveNode.bind(this);
}
setActiveNode(name) {
this.setState({activeNode: name})
}
render() {
return(
<div className="padd_top">{
renderTree(
this.props.root || root,
this.setActiveNode,
this.state.activeNode
)
}
</div>
)
}
}
I'm recently getting to know React.js and I'm very thankful for any advice/clarity you can provide.
Thank you.
You need to use lift state method passing state from child to parent then from parent pass it to the child you want
In your parent component create a constructor with states then create liftStateUp function pass it to the child component that you want to receive the data from
constructor(props) {
super(props)
this.state = {
activeNode: '',
}
}
liftStateUp = (data) =>{
this.setState({ activeNode: data})
}
<div>
<div className="col-md-6">
<FileTree liftStateUp={this.liftStateUp} />
</div>
<div className="col-md-6">
<TextBox content={this.state.activeNode} />
</div>
</div>
Then in file_tree.js FileTree function you need to call liftStateUp function that we created it in the parent component
setActiveNode(name) {
this.setState({ activeNode: name });
this.props.liftStateUp(name);
}
https://reactjs.org/docs/lifting-state-up.html
Props are passed down from the parent component to child component. You need to work with global store so that you can interact with state in different siblings of components. For this, you may use redux.
If your application size is smaller, then you may also try using context api.
Hope, this helps to you.

Rendering component with its state

I'm really confused now about lifecycle hooks. Here's my code:
App.js:
class App extends Component {
constructor(props){
super(props);
this.state = {
arrayOfComponents: []
}
}
componentDidMount(){
//i get the properties from the server which responds with the database's elements
fetch('http://localhost:3001/')
.then(res => res.json())
.then(arrayOfData => this.setState({arrayOfComponents: arrayOfData}))
.catch(err => console.log(err))
}
render() {
console.log(this.state) //first returns empty array, after the mount returns the db's array of elements
return (
<div className="App">
<Component name='First' id={1} componentsComponents={this.state.arrayOfComponents} />
</div>
);
}
}
Component.js:
class Component extends React.Component{
constructor(props){
super(props);
this.state={
componentsComponents: []
}
}
//here i was tried with componentDidMount, componentWillMount to set the
//this.props.componentsComponents to this.state.componentsComponents
//but it didn't work
renderComponents = () => {
if(this.state.componentsComponents.length){
return this.state.componentsComponents.filter(c => c.inhertedFromId === this.props.id).map(c => {
return <Component name={c.name} id={c.id} componentsComponents={this.props.componentsComponents} />
})
}
}
render(){
return(
<div>
{this.renderComponents()}
</div>
)
}
}
So what i want to do is to the components renders themselves, depending on the array they get from the App.js. But how to set the state before the render happens? Can i somehow ask the component to render again if it did mount? Or any other solutions?
You can simply assign this.props.componentsComponents in constructor itself only.
constructor(props){
super(props);
this.state={
componentsComponents: this.props.componentsComponents||[]
}
}
Bring Filter Up To App
Here it appears you are not calling renderComponents, and you are also trying to render a Component inside itself, which is difficult to reason about. Bring the renderComponents function up to App, and render the data using Component inside of App, and simply pass props down to a stateless Component, which may be a simpler solution to represent the data.
If a recursive call is indeed the best way to represent this data, may need to use getDerivedStateFromProps to move props into state on update, if you wish to store that data in state - something like:
static getDerivedStateFromProps(nextProps) {
return {
componentsComponents: nextProps.componentsComponents
}
}
Added to Component.

Pass variable from one component to another ReactJS

I am woking on a sample ReactJS application, where I want to pass a variable from one component to another.
class Layout extends React.Component{
constructor(props) {
super(props);
this.state = {keyword: ''};
}
render() {
return (
<div className="wrapper">
<Search />
<Listing />
</div>
);
}
};
ReactDOM.render(
<Layout />, app
);
In the above code, I want to pass a variable from <Search /> component to <Listing /> component.
Rlijo you'd pass props to components as follows:
<Search paramA={someParam} paramB={anotherParam} />
and to use the props within the Search component you'd call this.props.paramA (if using classes).
The way you've got the components setup, you wouldn't be able to share the state from the Search component (i.e. the object in this.state within Search) with the Listing component. There are libraries such as Redux designed to solve problems of shared state across components.
Props (or variables or params) flow downward so you'd need to provide shared props from a parent component. See you could provide this.state.keyword as a prop to both Search and Listing as these two components sit inside this parent component.
You can make it with function like
class Layout extends React.Component {
constructor(props) {
super(props);
this.state = {
keyword: '',
yourVariable: null
};
}
sendVariable(newValue) {
this.setState({ yourVariable: newValue });
}
render() {
return (
<div className="wrapper">
<Search onChange={this.sendVariable.bind(this)} />
<Listing sendValue={this.state.yourVariable} />
</div>
);
}
};
class Search extends React.Component{
render(){
let variable = "";
return <div onClick={this.porps.onChange(variable)}></div>;
}
}
Or use React-redux.

Reactjs:Is it possible to use Parent component property from another Parent's child component

I have a file named separatefile.jsx, in this file parent component name is Content and child component name is Child.
separatefile.jsx
import React from 'react';
import Parent from './learning.jsx';
class Content extends React.Component {
constructor() {
super();
this.state = {
finding : 'i am finding'
}
}
render() {
return (
<div>
<Child childprop={this.state.finding}/>
<Parent/>
</div>
);
}
}
class Child extends React.Component {
render() {
return (
<div>
<h2>{this.props.childprop}</h2>
<h1>child class property</h1>
</div>
);
}
}
export default Content;
This is another file named as learning.jsx , this file has Parent component named as Parent and Child component named as a Children.
My questions is that i need to access Parent component property(parent component for learning.jsx) from Child component(child component for separatefile.jsx file)...
learning.jsx
import React from 'react';
class Parent extends React.Component {
constructor() {
super();
this.state = {
searching : 'i will find the solution'
}
}
render() {
return (
<div>
<Children childrenprop={this.state.searching}/>
</div>
);
}
}
class Children extends React.Component {
render() {
return (
<div>
<h2>{this.props.childrenprop}</h2>
</div>
);
}
}
export default Parent;
If I understood you correctly, you want to use Parent's state in your Children component?
You can pass it down the component tree as props, e.g.:
class Content extends React.Component {
constructor() {
super();
this.state = {
finding : 'i am finding'
}
}
render() {
return (
<div>
<Child childprop={this.state.finding}/>
<Parent finding={this.state.finding} />
</div>
);
}
}
class Parent extends React.Component {
constructor() {
super();
this.state = {
searching : 'i will find the solution'
}
}
render() {
return (
<div>
<Children finding={this.props.finding} childrenprop={this.state.searching}/>
</div>
);
}
}
class Children extends React.Component {
render() {
return (
<div>
<h2>{this.props.childrenprop}</h2>
<div>{this.props.finding}</div>
</div>
);
}
}
It's probably not a direct answer but if you are starting a new app I would recommend you to use Redux with react-redux.
Redux is a predictable state container for JavaScript apps.
It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. On top of that, it provides a great developer experience, such as live code editing combined with a time traveling debugger.
It's very small library so it's easy to understand how everything works. It might be a good solution to your problem.
Todo app example
You can also check out awesome egghead.io free tutorial - Getting Started with Redux
Here is the answer about the redux benefits by its author Dan Abramov
The React documentation provides an answer.
For communication between two components that don't have a
parent-child relationship, you can set up your own global event
system. Subscribe to events in componentDidMount(), unsubscribe in
componentWillUnmount(), and call setState() when you receive an event.
Flux pattern is one of the possible ways to arrange this.

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