异步 Function 调用父组件

Question

I have this

const Parent = () => {
    [modalOpen, setModal] = React.useState(false);

    return <Child
               open={modalOpen}
               closeModal={() => setModal(false)}
               functionFromParent={() => console.log('Logged')} />
}

and that

const Child = ({ functionFromStore, functionFromParent, closeModal }) => {
    async function foo() {
        try {
          await ...;
          functionFromStore();
          functionFromParent();
        } catch (error) {
          ....
        }
    }

    const bar = () => {
        foo();
        closeModal();
    }

    return <div
           style={{backgroundColor: 'hotpink', width: '10rem', height: '10rem' }}
           onClick={() => bar()}/>
}

component.

<Parent /> decides if the <Child /> (it is a Modal ) shown or not. <Child /> has three functions, closeModal() and functionFromParent() , coming from the <Parent/ > . And functionFromStore() coming from redux through dispatchToProps() . For the sake of simplicity I left all the connect(stateToProps, dispatchToProps)(...) stuff out. But lets assume <Child /> is directly connected to the store .

Clicking on the <div /> in <Child/> executes bar() . That causes <Child /> to unmount , because closeModal() in the <Parent /> is called, closing the modal . However, bar() also calls foo() , being a async function.

When the await is resolved, the functionFromStore() is called, but not the functionFromParent() . I wonder why is that? Why is a function coming from the store called, even when the component ( <Child /> ) is unmounted, but not the function coming from the parent?

Further, is there a way to call functionFromParent() , even when <Child /> is unmounted? Somehow it works with functionFromStore() , is there a way to make it work with functionFromParent() ?

Answer 1

I cannot reproduce the behavior you describe but it's probably a closure problem as you're setting the state multiple times but have a stale state value in the closure of your handlers

You can solve it by passing a callback to the state setter: setSomeState(currentState=>({...currentState,changes})) , here is a full example:

 function Parent() { const [state, setState] = React.useState({ showModal: true, showFoo: false, }); return ( <div> {state.showModal? ( <Child open={state.showModal} closeModal={() => setState(state => ({...state, showModal: false, })) } functionFromParent={() => setState(state => ({...state, showFoo: true, })) } /> ): ( 'Child is gone ' )} {state.showFoo? <Foo />: 'no foo'} </div> ); } function Child({ functionFromParent, closeModal }) { function foo() { setTimeout(() => { functionFromParent(); }, 1000); } const bar = () => { foo(); closeModal(); }; return <button onClick={bar}>click me</button>; } function Foo() { return 'hi, I am Foo'; } ReactDOM.render( <Parent />, document.getElementById('root') );

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.4/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.4/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 2

functionFromParent must have been called. There must be something else that causing the problem.

 const Parent = () => { const [showChild, setShowChild] = React.useState(true); const childProps = { fnFromParent: () => { console.log("logging from fnFromParent"); }, unmount: () => { setShowChild(false); } }; return ( <div> <p>I'm a Parent</p> { showChild && <Child {...childProps} /> } </div> ); }; const Child = ({ fnFromParent, unmount }) => { const delayed = () => { const p = new Promise(res => setTimeout(res, 3000)) p.then(() => fnFromParent()); }; const clickHandler = () => { delayed(); unmount(); }; return <p onClick={clickHandler}>I'm a Child (click to remove me)</p>; }; ReactDOM.render(<Parent />, document.getElementById("root"));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 3

function Parent() {
  const [modalOpen, setModal] = React.useState(false);

  return (
    <Child
      open={modalOpen}
      closeModal={() => setModal(false)}
      functionFromParent={() => console.log("Logged")}
    />
  );
}

is there a way to call functionFromParent(), even when is unmounted? Somehow it works with functionFromStore(), is there a way to make it work with functionFromParent()?

• Yes! When your component unmount, you can perform a cleanup which is provided by React hooks' useEffect . You can see the code below, once you click your div , props.closeModal is invoked, which will unmount your Child component. Once the component unmount, useEffect then performs a clean up which is in the return block of the useEffect, which calls your functionFromParent and functionFromStore .

function Child(props) {
  useEffect(() => {
    return () => {
      props.functionFromStore();
      props.functionFromParent();
    };
  });

  return (
    <div
      style={{ backgroundColor: "hotpink", width: "10rem", height: "10rem" }}
      onClick={props.closeModal}
    />
  );
}