当状态是对象数组时更新状态。反应

Question

我正在通过使用上下文来处理购物车的问题。我的问题是改变有一个对象数组的状态。

我的数组看起来像这个[{itemId: 'ps-5', qty:4}, {itemId: 'iphone-xr', qty:2}]

这是我的代码--检查注释

export const CartContext = createContext()

class CartContextProvider extends Component {

    state = {
        productsToPurchase: []
    }

    addProduct = (itemId)=> {
        if (JSON.stringify(this.state.productsToPurchase).includes(itemId)){
            // Add one to the qty of the product
            this.state.productsToPurchase.map(product=>{
                if (product.itemId === itemId){
                    // This is wrong I have to use setState(), but the syntax is a little bit complex
                    product.qty = product.qty + 1
                }
            })
        }
        else {
            this.state.productsToPurchase.push({itemId: itemId, qty: 1})
        }
    }

    render() {
        return (
            <CartContext.Provider value={{...this.state, addProduct: this.addProduct}}>
                {this.props.children}
            </CartContext.Provider>
        )
    }
}

export default CartContextProvider;

Answer 1

您正在直接更新状态，但是您必须使用this.setState更新它，

现场演示

​

​

addProduct = (itemId) => {
  this.setState((oldState) => {
    const objWithIdExist = oldState.productsToPurchase.find((o) => o.itemId === itemId);
    return {
      productsToPurchase: !objWithIdExist
        ? [...oldState.productsToPurchase, { itemId, qty: 1 }]
        : oldState.productsToPurchase.map((o) =>
            o.itemId !== itemId ? o : { ...o, qty: o.qty + 1 }
          )
    };
  });
};