React Native useEffect - 警告：除了用於清理的函數之外，效果函數不得返回任何內容

Question

我想實現一個功能來檢查是否預訂了 20 個可用座位之外的特定座位。 如果是，則返回紅色，如果不是，則返回綠色。

我將獲取功能實現為

const getSeatColor = (seat, vid) => {
    const [color, setColor] = useState(0);

    useEffect(async () => {
      const response = await fetch(
        `http://192.168.8.100/dbops/actions/seat_status.php?seat=${seat}&vid=${vid}`
      );
      const result = await response.json();
      setColor(result.message);
    }, []);

    return color;
  };

  const vid = 4;
  const seat1Color = getSeatColor(1, vid);
  const seat2Color = getSeatColor(2, vid);
  const seat3Color = getSeatColor(3, vid);
  const seat4Color = getSeatColor(4, vid);

return (
    <Screen style={{ paddingBottom: 5 }}>
         {/* Seat 1 starts */}
          <TouchableOpacity style={styles.seat} >
            <MaterialCommunityIcons name="seat" size={40} color={seat1Color} />
            <Button title="1" style={{ width: 20 }} color={seat1Color} />
          </TouchableOpacity>
          {/* Seat 1 ends */}
          {/* Seat 2 starts */}
          <TouchableOpacity style={styles.seat} >
            <MaterialCommunityIcons name="seat" size={40} color={seat2Color} />
            <Button title="2" style={{ width: 20 }} color={seat2Color} />
          </TouchableOpacity>
          {/* Seat 2 ends */}
          <View style={styles.seat}></View>
          <View style={styles.seat}></View>
          {/* Seat 3 starts */}
          <TouchableOpacity style={styles.seat} >
            <MaterialCommunityIcons name="seat" size={40} color={seat3Color} />
            <Button title="3" style={{ width: 20 }} color={seat3Color} />
          </TouchableOpacity>
     </Screen>
)

綠色或紅色顯示正常，但我收到此警告：效果函數不得返回除用於清理的函數之外的任何內容。

我試過這個How to call an async function inside a UseEffect() in React? 但同樣的警告彈出。 請幫忙或者有其他方法可以實現這一目標嗎？

Answer 1

您將直接使用 async 關鍵字作為回調參數返回一個承諾。 嘗試像這樣重寫你的 useEffect：

 useEffect(() => { (async() => { const response = await fetch( `http://192.168.8.100/dbops/actions/seat_status.php?seat=${seat}&vid=${vid}` ); const result = await response.json(); setColor(result.message); })() }, []);

或者將該代碼包裝在另一個函數中並在 useEffect 中調用它

 const fetchData = async () => { const response = await fetch( `http://192.168.8.100/dbops/actions/seat_status.php?seat=${seat}&vid=${vid}` ); const result = await response.json(); setColor(result.message); } useEffect(() => { fetchData(); }, []);

Answer 2

useEffect 不接受異步函數。

你可以嘗試做這個：

const getSeatColor = (seat, vid) => {
    const [color, setColor] = useState(0);

    useEffect(() => {
      (async => {
         const response = await fetch(`http://192.168.8.100/dbops/actions/seat_status.php?seat=${seat}&vid=${vid}`);
         const result = await response.json();
         setColor(result.message);
      })();
    }, []);

    return color;
};