How to pass state back to parent in React?

问题

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>
    )

回答1:

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}/>

回答2:

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">

回答3:

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.

回答4:

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.

来源：https://stackoverflow.com/questions/40722382/how-to-pass-state-back-to-parent-in-react