react-native - useState 在重新渲染时不断重置为 initialValue

Question

所以我的屏幕代码看起来像这样。我有一个 useState amount，它在重新呈现时不断重置为 initialValue。我有大约 3 个 useEffects。其中之一在此处的示例代码中，我从数据库中获取数量并使用 setAmount 进行设置。

    const ConfirmPaymentDialog = props => {
       const getInitialVal = () => {
          console.log('Initial Amount: 0');
          return conversions.numberToBigNumber(0);
       };
       const [amount, setAmount] = useState<BigNumber>(getInitialVal());
    
       useEffect(() => {
           getAmountToPay();
       },[]);
    
       const getAmountToPay = async () => {
        const amount = await myDbModule.getAmount(customer.id);
        console.log('DB Amount: ' + amount?.toString());
        setAmount(amount || conversions.numberToBigNumber(0));
      };
    
       useEffect(() => {
       ...
       }, [isInputTextFocused])
    
      console.log('Rendering');
      return (<View>...</View>);
    }

当我打开这个屏幕时。我得到以下控制台日志

 LOG  Initial Amount: 0
 LOG  Rendering
 LOG  DB Amount: 500
 LOG  Initial Amount: 0
 LOG  Rendering
 LOG  Initial Amount: 0
 LOG  Rendering
 LOG  Initial Amount: 0
 LOG  Rendering
 LOG  Initial Amount: 0
 LOG  Rendering
 LOG  Initial Amount: 0
 LOG  Rendering

如何阻止我的 useState 在重新渲染时重置回默认值

Answer 1

它实际上并没有重置为初始值。您只需继续调用生成初始值的函数即可。不要调用它，而是将它作为回调(参见 lazy initial state )传递给 useState() Hook ，它将被调用一次:

const [amount, setAmount] = useState<BigNumber>(getInitialVal); // getInitialVal instead of getInitialVal()