1 回答

TA貢獻1860條經驗 獲得超8個贊
這inProgress
是傳遞給 setInterval 的函數的陳舊閉包。
可以通過清除cleanup函數中的interval來解決:
const Clock = ({ dispatch, inProgress, ticksElapsed }) => {
React.useEffect(() => {
const progressTimer = setInterval(function () {
inProgress && dispatch({ type: 'CLOCK_RUN' });
}, 500);
return () =>
//inprogress is stale so when it WAS true
// it must now be false for the cleanup to
// be called
inProgress && clearInterval(progressTimer);
}, [dispatch, inProgress]);
return <h1>{ticksElapsed}</h1>;
};
const App = () => {
const [inProgress, setInProgress] = React.useState(false);
const [ticksElapsed, setTicksElapsed] = React.useState(0);
const dispatch = React.useCallback(
() => setTicksElapsed((t) => t + 1),
[]
);
return (
<div>
<button onClick={() => setInProgress((p) => !p)}>
{inProgress ? 'stop' : 'start'}
</button>
<Clock
inProgress={inProgress}
dispatch={dispatch}
ticksElapsed={ticksElapsed}
/>
</div>
);
};
ReactDOM.render(<App />, document.getElementById('root'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.4/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.4/umd/react-dom.production.min.js"></script>
<div id="root"></div>
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