反应：将 Child1 state 值传递给 Parent 并从 parent 传回 Child2

Question

In my app I have two child components, 'FoodScreen', 'OperationScreen' and a parent Component 'Desk'. Am passing a Json variable array to FoodScreen component to select the item.

When I press the button in Child1 component, it should pass the value for parent, and then the parent should pass the value for child2

Desk Component as:

const nameList = [
        {
            "id": 111,
            "name": "Leanne Graham",
            "username": "Bret"
            }
        },
        {
            "id": 112,
            "name": "Ervin Howell",
            "username": "Antonette"
            }
        }
    ];

    let selectedItem = null;
    let item = (selectedItem == null) ? 0 : nameList.find(x => x.id === selectedItem);

class SalesDesk extends Component {

    render() {
        return <div>
            <div className="Background">
                <Header/>
                <div className="Main">
                    <FoodScreen itemlist={nameList}/>
                    <OperationScreen item={item}/>
                </div>
                <Footer/>
            </div>
        </div>
    }
} 

where a 'select ID' state is updated by a click event in the 'FoodScreen Component', like so:

class SdFoodScreen extends Component {
  render() {
    return <div className="sdFoodScreenMain">
        {
            this.props.itemlist.map(items =>
                <div className="sdFoodBoxes" key={items.id}>
                  {items.id}
                  {items.name}
                  <button onClick={() => this.selectItem(items.id)}> Select ID </button>
                </div>
            )
        }
    </div>;
  }

  constructor(props) {
    super(props);
    this.state = {
      selectedItem : null
    }
  }

  selectItem(itemID) {
    this.setState({
      selectedItem : itemID
    })
  }
}

And My 2nd Child component as:

class OperationScreen extends Component {
  render() {
    let selectedItem = this.props.item;
    console.log(selectedItem);
  }
}

Whenever I click the button in FoodScreen component, the value should be passed to the Parent 'Salesdesk' component, so I could go pass the value to Child2 component, and print on the console.

I would prefer I there is a way to get rid of the If condition in the Parent class, to have better code structure, as am new to React.

Answer 1

You will need to pass a callback function to a child element to update a value in the parent class. You can restructure it in the following way -

In FoodScreen , update the onClick handler to call the callback function and pass the item as an argument -

...
<button onClick={() => this.props.onSelect(item)}> Select ID </button>
...

Then on the SalesDesk class, you can pass the callback handler while using the FoodScreen component

<FoodScreen itemlist={nameList} onSelect={this.updateSelection}/>

and you can update the selected item using this new callback function

updateSelected = (item) => {
  this.setState({selectedItem: item});
}

now you can pass selectedItem to OperationScreen

<OperationScreen item={selectedItem}/>

EDIT:

See Demo