反应本机间隔状态不更新 [英] React native interval state not updating

问题描述

状态更改中的间隔函数不起作用，请帮帮我.

interval function in state change not working help me please.

状态不变

function Home({ route, navigation }) {
const [ marker, setMarker ] = useState(0);

_stropeText = () => {
  if (marker == 0){
   setMarker(marker => 1);
  } else {
   setMarker(marker => 0);
  }
}

React.useEffect(() => {
    setLoading(true);
    const unsubscribe = navigation.addListener('focus', () => {
      setInterval(_stropeText, 500);
    });
    return () => {  };
  }, [navigation]);
}

https://snack.expo.io/Hbedd4HVh

推荐答案

你 在 marker 值上有一个闭包，将它添加到 useEffect 依赖数组，或者使用带有 useRef 钩子的引用.

You have a closure on marker value, add it to useEffect dependency array, or use a reference with useRef hook.

此外，您将回调传递给 useState，它使 功能更新，这里不是这种情况.

Also, you passing a callback to useState, it makes functional updates, which is not the case here.

function Home({ route, navigation }) {
  const [marker, setMarker] = useState(0);

  React.useEffect(() => {
    setLoading(true);
    const _stropeText = () => {
      if (marker === 0) {
        setMarker(1);
      } else {
        setMarker(0);
      }
    };
    const unsubscribe = navigation.addListener("focus", () => {
      setInterval(_stropeText, 500);
    });
    return () => {
      /*remove listener*/
    };
  }, [navigation, marker]);
}

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