How to pass state back to parent in React?

I have a form that has a submit button. That form calls a function onclick that sets the state of something from false to true. I then want to pass this state back to the parent so that if it is true it renders componentA but if it is false it renders componentB.

How would I do that in react? I know I need to use state or props but not sure how to do it. also is this contradicting the one-way flow react principle??

ComponentA code:

<form onSubmit={this.handleClick}>


handleClick(event) {
    this.setState({ decisionPage: true });
    event.preventDefault();
  };

Parent component that controls what it displays:

return (
      <div>
      {this.props.decisionPage ?
        <div>
          <LoginPage />
        </div>
        :
        <div>
          <Decision showThanks={this.props.showThanks}/>
        </div>
      }
      </div>
    )

Move handleClick to the parent and pass it to the child component as a prop.

<LoginPage handleClick={this.handleClick.bind(this)}/>

Now in the child component:

<form onSubmit={this.props.handleClick}>

This way submitting the form will update the state in parent component directly. This assumes you don't need to access updated state value in child component. If you do, then you can pass the state value back from the parent to the child as a prop. One-way data flow is maintained.

<LoginPage  handleClick={this.handleClick.bind(this)} decisionPage={this.state.decisionPage}/>

Pass State as a Prop

I have recently learned a method that works great for changing state in a <Parent /> component from a <Child /> component.

This might not be the exact answer for this question, but it is surely applicable to this situation and other similar situations.

It works like this:

set the default STATE in the <Parent /> component - Then add the 'setState' attribute to the <Child />

const Parent = () => {
  const [value, setValue] = useState(" Default Value ");
   return (
    <Child setValue={setValue} />
  )
}

Then change the state(in Parent) from the Child component

const Child = props => {
  return (
   <button onClick={() => props.setValue(" My NEW Value ")}>
    Click to change the state
  </button>
 )
}

When you click the button, the state in the <Parent /> component will change to whatever you set the state to in the <Child /> component, making use of "props".. This can be anything you want.

I Hope this helps you and other devs in the future.

In Parent Component:

getDatafromChild(val){
    console.log(val);
}
render(){
 return(<Child sendData={this.getDatafromChild}/>);
}

In Child Component:

callBackMethod(){
   this.props.sendData(value);
 }

Simple Steps:

1. Create a component called Parent.

2. In Parent Component create a method that accepts some data and sets the accepted data as the parent's state.

3. Create a component called Child.

4. Pass the method created in Parent to child as props.

5. Accept the props in parent using this.props followed by method name and pass child's state to it as argument.

6. The method will replace the parent's state with the child's state.

Here is an example of how we can pass data from child to parent (I had the same issue and use come out with this )

On parent, I have a function (which I will call from a child with some data for it)

handleEdit(event, id){ //Fuction
    event.preventDefault();  
    this.setState({ displayModal: true , responseMessage:'', resId:id, mode:'edit'});  
 } 

dishData = <DishListHtml list={products} onDelete={this.handleDelete} onEdit={(event, id) => this.handleEdit(event, id)}/>;

At the child component :

<div to="#editItemDetails" data-toggle="modal" onClick={(event)=>this.props.onEdit(event, listElement.id) }
                        className="btn btn-success">

In React you can pass data from parent to child using props. But you need a different mechanism to pass data from child to parent.

Another method to do this is to create a callback method. You pass the callback method to the child when it's created.

class Parent extends React.Component {
myCallback = (dataFromChild) => {
    //use dataFromChild
},
render() {
    return (
        <div>
             <ComponentA callbackFromParent={this.myCallback}/>
        </div>
    );
  }
}

You pass the decisionPage value from the child to the parent via the callback method the parent passed.

     class ComponentA extends React.Component{
          someFn = () => {
            this.props.callbackFromParent(decisionPage);
          },
          render() {
            [...]
          }
     };

SomeFn could be your handleClick method.

if your parent component is a functional component you can now use the use context way. Which involves passing the ref to the object and the ref to the stateChanging method. What this will allow you to do is change state from parrent in child and also ref tht state while remaining synced with Parent State. You can learn more about this in a youtubeVideo by codedamn titled 'React 16.12 Tutorial 20: Intro to Context API' and 'React 16.12 Tutorial 21: useContext'

This works exactly what I wanted. But in case of set of data with say 50 records with (customer_id, customer_name) as values to be updated from child to parent, then this lags. Do the setState using React.useEffect in child component