在 onclick 中調用 function 后 React.js 不增加

Question

我需要建立一個表格來組織一些數據。 我正在使用“onclick”function 來調用單獨的 function，這應該將 state 變量增加一。 我的 Chrome Devtools 沒有給我任何錯誤，但也沒有更新 stock 變量。 我不確定如何讓 state 更新和顯示。 這是我的源代碼：

class App extends React.Component {
    constructor(props) {
        super(props);

        this.state = {
            cars: [
                {
                    manufacturer: "Toyota",
                    model: "Rav4",
                    year: 2008,
                    stock: 3,
                    price: 8500
                },
    
                {
                    manufacturer: "Toyota",
                    model: "Camry",
                    year: 2009,
                    stock: 2,
                    price: 6500
                },
    
                {
                    manufacturer: "Toyota",
                    model: "Tacoma",
                    year: 2016,
                    stock: 1,
                    price: 22000
                },
    
                {
                    manufacturer: "BMW",
                    model: "i3",
                    year: 2012,
                    stock: 5,
                    price: 12000
                },
    
            ]
        };
        this.renderCar = this.renderRow.bind(this);
        this.handleClick = this.handleClick.bind(this);
    }

    handleClick() {
        this.setState(() => {
            return {stock: this.stock + 1}
        })
    }

    renderRow(car, index) {
        return (
            <tr key={index}>
                <td key={car.manufacturer}>{car.manufacturer}</td>
                <td key={car.model}>{car.model}</td>
                <td key={car.year}>{car.year}</td>
                <td key={car.stock}>{car.stock}</td>
                <td key={car.price}>${car.price}.00</td>
                <td key={index}><input type="button" onClick={car.handleClick} value="Increment" /></td>
            </tr>
        )
    }

    render() {
        return (
            <div>
            <table>
                <thead>
                <tr>
                    <th>Manufacturer</th>
                    <th>Model</th>
                    <th>Year</th>
                    <th>Stock</th>
                    <th>Price</th>
                    <th>Option</th>
                </tr>
                </thead>
                <tbody>
                    {this.state.cars.map(this.renderRow)}
                </tbody>
            </table>
            </div>
        );
    };
}

ReactDOM.render(<App />, document.getElementById("app"))

Answer 1

我會為該行創建一個單獨的組件，以便您可以輕松地更新該組件以增加 state 中的stock值：

 class App extends React.Component { constructor(props) { super(props); this.state = { cars: [ { manufacturer: "Toyota", model: "Rav4", year: 2008, stock: 3, price: 8500 }, { manufacturer: "Toyota", model: "Camry", year: 2009, stock: 2, price: 6500 }, { manufacturer: "Toyota", model: "Tacoma", year: 2016, stock: 1, price: 22000 }, { manufacturer: "BMW", model: "i3", year: 2012, stock: 5, price: 12000 }, ] }; } render() { return ( <div> <table> <thead> <tr> <th>Manufacturer</th> <th>Model</th> <th>Year</th> <th>Stock</th> <th>Price</th> <th>Option</th> </tr> </thead> <tbody> {this.state.cars.map( (car, i) => <Row car={car} key={i} /> )} </tbody> </table> </div> ); }; } const Row = ({ car }) => { const [stock, setStock] = React.useState(car.stock); return ( <tr> <td>{car.manufacturer}</td> <td>{car.model}</td> <td>{car.year}</td> <td>{stock}</td> <td>${car.price}.00</td> <td><input type="button" onClick={() => setStock(stock + 1)} value="Increment" /></td> </tr> ); } ReactDOM.render(<App />, document.getElementById("app"))

 <script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script> <script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script> <div id='app'></div>

如果必須，您可以將它們全部放在一個組件中，但這會有點麻煩。 在渲染時，您必須跟蹤一行的渲染索引並將其傳遞給單擊處理程序，然后在該索引處不可變地更新 state 數組中的stock屬性。 單獨的組件更容易。

Answer 2

   handleClick(e){
      const index = Number(e.currentTarget.value);
      this.setState(this.state.cars.map(car, i)=> {
        return i === index ? {...car, stock: car.stock + 1}: car 
      })
   }
 
   renderRow(){
    ....
       <input type="button" onClick={this.handleClick} value={index} />
    ...
   }