使用setTimeout延迟反应useEffect中的setInterval
我想在它第一次触发时运行一个有延迟的间隔。我该如何使用useEffect？由于语法原因，我发现很难实现我想做的事情
间隔函数
useEffect(()=>{
const timer = setInterval(() => {
//do something here
return ()=> clearInterval(timer)
}, 1000);
},[/*dependency*/])
延迟功能
useEffect(() => {
setTimeout(() => {
//I want to run the interval here, but it will only run once
//because of no dependencies. If i populate the dependencies,
//setTimeout will run more than once.
}, Math.random() * 1000);
}, []);
当然可以实现...
4 个答案:
答案 0 :(得分：1)
我认为您要这样做的是
const DelayTimer = props => {
const [value, setvalue] = React.useState("initial");
const [counter, setcounter] = React.useState(0);
React.useEffect(() => {
let timer;
setTimeout(() => {
setvalue("delayed value");
timer = setInterval(() => {
setcounter(c => c + 1);
}, 1000);
}, 2000);
return () => clearInterval(timer);
}, []);
return (
<div>
Value:{value} | counter:{counter}
</div>
);
};
// Render it
ReactDOM.render(<DelayTimer />, document.getElementById("react"));<div id="react"></div>
<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></script>
答案 1 :(得分：1)
入门
请考虑整理组件的问题并编写小片段。这里我们有一个useInterval自定义钩子，它严格定义了程序的setInterval部分。我添加了一些console.log行，以便我们观察效果-
// rough draft
// read on to make sure we get all the parts right
function useInterval (f, delay)
{ const [timer, setTimer] =
useState(null)
const start = () =>
{ if (timer) return
console.log("started")
setTimer(setInterval(f, delay))
}
const stop = () =>
{ if (!timer) return
console.log("stopped", timer)
setTimer(clearInterval(timer))
}
useEffect(() => stop, [])
return [start, stop, timer != null]
}
现在，当我们编写MyComp时，我们可以处理程序的setTimeout部分-
function MyComp (props)
{ const [counter, setCounter] =
useState(0)
const [start, stop, running] =
useInterval(_ => setCounter(x => x + 1), 1000) // first try at useInterval
useEffect(() => {
console.log("delaying...")
setTimeout(() => {
console.log("starting...")
!running && start()
}, 2000)
}, [])
return <div>
{counter}
<button
onClick={start}
disabled={running}
children="Start"
/>
<button
onClick={stop}
disabled={!running}
children="Stop"
/>
</div>
}
现在，我们可以在程序的各个部分useInterval中使用，并且每个部分的使用方式都可以不同。启动，停止和清除的所有逻辑都很好地封装在钩子中。
这是一个演示，您可以运行以查看其工作原理-
const { useState, useEffect } = React
const useInterval = (f, delay) =>
{ const [timer, setTimer] = useState(undefined)
const start = () =>
{ if (timer) return
console.log("started")
setTimer(setInterval(f, delay))
}
const stop = () =>
{ if (!timer) return
console.log("stopped", timer)
setTimer(clearInterval(timer))
}
useEffect(() => stop, [])
return [start, stop, !!timer]
}
const MyComp = props =>
{ const [counter, setCounter] =
useState(0)
const [start, stop, running] =
useInterval(_ => setCounter(x => x + 1), 1000)
useEffect(() => {
console.log("delaying...")
setTimeout(() => {
console.log("starting...")
!running && start()
}, 2000)
}, [])
return <div>
{counter}
<button
onClick={start}
disabled={running}
children="Start"
/>
<button
onClick={stop}
disabled={!running}
children="Stop"
/>
</div>
};
ReactDOM.render
( <MyComp/>
, document.getElementById("react")
)<div id="react"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.1/umd/react-dom.production.min.js"></script></script>
正确处理
如果要停止计时器或移除组件后，我们想确保useInterval钩子不会让任何定时功能运行。让我们在更严格的示例中对其进行测试，在该示例中，我们可以添加/删除许多计时器并随时启动/停止-
需要对useInterval进行一些基本更改-
function useInterval (f, delay = 1000)
{ const [busy, setBusy] = useState(0)
useEffect(() => {
// start
if (!busy) return
setBusy(true)
const t = setInterval(f, delay)
// stop
return () => {
setBusy(false)
clearInterval(t)
}
}, [busy, delay])
return [
_ => setBusy(true), // start
_ => setBusy(false), // stop
busy // isBusy
]
}
在useInterval组件中使用MyTimer很直观。不需要MyTimer进行间隔的任何形式的清理。清除由useInterval-
function MyTimer ({ delay = 1000, auto = true, ... props })
{ const [counter, setCounter] =
useState(0)
const [start, stop, busy] =
useInterval(_ => {
console.log("tick", Date.now()) // <-- for demo
setCounter(x => x + 1)
}, delay)
useEffect(() => {
console.log("delaying...") // <-- for demo
setTimeout(() => {
console.log("starting...") // <-- for demo
auto && start()
}, 2000)
}, [])
return <span>
{counter}
<button onClick={start} disabled={busy} children="Start" />
<button onClick={stop} disabled={!busy} children="Stop" />
</span>
}
Main组件没有做任何特殊的事情。它仅管理MyTimer个组件的数组状态。不需要特定于计时器的代码或清除-
const append = (a = [], x = null) =>
[ ...a, x ]
const remove = (a = [], x = null) =>
{ const pos = a.findIndex(q => q === x)
if (pos < 0) return a
return [ ...a.slice(0, pos), ...a.slice(pos + 1) ]
}
function Main ()
{ const [timers, setTimers] = useState([])
const addTimer = () =>
setTimers(r => append(r, <MyTimer />))
const destroyTimer = c => () =>
setTimers(r => remove(r, c))
return <main>
<button
onClick={addTimer}
children="Add Timer"
/>
{ timers.map((c, key) =>
<div key={key}>
{c}
<button
onClick={destroyTimer(c)}
children="Destroy"
/>
</div>
)}
</main>
}
展开下面的代码片段，即可查看useInterval在您自己的浏览器中的运行情况。建议此演示使用全屏模式-
const { useState, useEffect } = React
const append = (a = [], x = null) =>
[ ...a, x ]
const remove = (a = [], x = null) =>
{ const pos = a.findIndex(q => q === x)
if (pos < 0) return a
return [ ...a.slice(0, pos), ...a.slice(pos + 1) ]
}
function useInterval (f, delay = 1000)
{ const [busy, setBusy] = useState(0)
useEffect(() => {
// start
if (!busy) return
setBusy(true)
const t = setInterval(f, delay)
// stop
return () => {
setBusy(false)
clearInterval(t)
}
}, [busy, delay])
return [
_ => setBusy(true), // start
_ => setBusy(false), // stop
busy // isBusy
]
}
function MyTimer ({ delay = 1000, auto = true, ... props })
{ const [counter, setCounter] =
useState(0)
const [start, stop, busy] =
useInterval(_ => {
console.log("tick", Date.now())
setCounter(x => x + 1)
}, delay)
useEffect(() => {
console.log("delaying...")
setTimeout(() => {
console.log("starting...")
auto && start()
}, 2000)
}, [])
return <span>
{counter}
<button
onClick={start}
disabled={busy}
children="Start"
/>
<button
onClick={stop}
disabled={!busy}
children="Stop"
/>
</span>
}
function Main ()
{ const [timers, setTimers] = useState([])
const addTimer = () =>
setTimers(r => append(r, <MyTimer />))
const destroyTimer = c => () =>
setTimers(r => remove(r, c))
return <main>
<p>Run in expanded mode. Open your developer console</p>
<button
onClick={addTimer}
children="Add Timer"
/>
{ timers.map((c, key) =>
<div key={key}>
{c}
<button
onClick={destroyTimer(c)}
children="Destroy"
/>
</div>
)}
</main>
}
ReactDOM.render
( <Main/>
, document.getElementById("react")
)<div id="react"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.1/umd/react-dom.production.min.js"></script></script>
进阶
让我们想象一个更加复杂的useInterval场景，其中定时函数f和delay可以改变-
function useInterval (f, delay = 1000)
{ const [busy, setBusy] = // ...
const interval = useRef(f)
useEffect(() => {
interval.current = f
}, [f])
useEffect(() => {
// start
// ...
const t =
setInterval(_ => interval.current(), delay)
// stop
// ...
}, [busy, delay])
return // ...
}
现在，我们可以编辑MyTimer以添加doubler和turbo状态-
function MyTimer ({ delay = 1000, auto = true, ... props })
{ const [counter, setCounter] = useState(0)
const [doubler, setDoubler] = useState(false) // <--
const [turbo, setTurbo] = useState(false) // <--
const [start, stop, busy] =
useInterval
( doubler // <-- doubler changes which f is run
? _ => setCounter(x => x * 2)
: _ => setCounter(x => x + 1)
, turbo // <-- turbo changes delay
? Math.floor(delay / 2)
: delay
)
// ...
然后我们添加一个 double 和 turbo 按钮-
// ...
const toggleTurbo = () =>
setTurbo(t => !t)
const toggleDoubler = () =>
setDoubler(t => !t)
return <span>
{counter}
{/* start button ... */}
<button
onClick={toggleDoubler} // <--
disabled={!busy}
children={`Doubler: ${doubler ? "ON" : "OFF"}`}
/>
<button
onClick={toggleTurbo} // <--
disabled={!busy}
children={`Turbo: ${turbo ? "ON" : "OFF"}`}
/>
{/* stop button ... */}
</span>
}
展开以下代码段，以在您自己的浏览器中运行高级计时器演示-
const { useState, useEffect, useRef, useCallback } = React
const append = (a = [], x = null) =>
[ ...a, x ]
const remove = (a = [], x = null) =>
{ const pos = a.findIndex(q => q === x)
if (pos < 0) return a
return [ ...a.slice(0, pos), ...a.slice(pos + 1) ]
}
function useInterval (f, delay = 1000)
{ const interval = useRef(f)
const [busy, setBusy] = useState(0)
useEffect(() => {
interval.current = f
}, [f])
useEffect(() => {
// start
if (!busy) return
setBusy(true)
const t =
setInterval(_ => interval.current(), delay)
// stop
return () => {
setBusy(false)
clearInterval(t)
}
}, [busy, delay])
return [
_ => setBusy(true), // start
_ => setBusy(false), // stop
busy // isBusy
]
}
function MyTimer ({ delay = 1000, ... props })
{ const [counter, setCounter] =
useState(0)
const [doubler, setDoubler] = useState(false)
const [turbo, setTurbo] = useState(false)
const [start, stop, busy] =
useInterval
( doubler
? _ => setCounter(x => x * 2)
: _ => setCounter(x => x + 1)
, turbo
? Math.floor(delay / 2)
: delay
)
const toggleTurbo = () =>
setTurbo(t => !t)
const toggleDoubler = () =>
setDoubler(t => !t)
return <span>
{counter}
<button
onClick={start}
disabled={busy}
children="Start"
/>
<button
onClick={toggleDoubler}
disabled={!busy}
children={`Doubler: ${doubler ? "ON" : "OFF"}`}
/>
<button
onClick={toggleTurbo}
disabled={!busy}
children={`Turbo: ${turbo ? "ON" : "OFF"}`}
/>
<button
onClick={stop}
disabled={!busy}
children="Stop"
/>
</span>
}
function Main ()
{ const [timers, setTimers] = useState([])
const addTimer = () =>
setTimers(r => append(r, <MyTimer />))
const destroyTimer = c => () =>
setTimers(r => remove(r, c))
return <main>
<p>Run in expanded mode. Open your developer console</p>
<button
onClick={addTimer}
children="Add Timer"
/>
{ timers.map((c, key) =>
<div key={key}>
{c}
<button
onClick={destroyTimer(c)}
children="Destroy"
/>
</div>
)}
</main>
}
ReactDOM.render
( <Main/>
, document.getElementById("react")
)<div id="react"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.1/umd/react-dom.production.min.js"></script></script>
答案 2 :(得分：0)
如果您尝试在setInterval中使用useEffect，我想您将顺序调高了一点，应该是这样的
const INTERVAL_DELAY = 1000
useEffect(() => {
const interval = setInterval(() => {
/* do repeated stuff */
}, INTERVAL_DELAY)
return () => clearInterval(interval)
})
间隔将在延迟后开始，因此，如果您希望X间隔的间隔在Y秒之后开始，则必须在setTimeout中将延迟实际用作Y-X
const INITIAL_DELAY = 10000
const INTERVAL_DELAY = 5000
useEffect(() => {
let interval
setTimeout(() => {
const interval = setInterval(() => {
/* do repeated stuff */
}, INTERVAL_DELAY)
}, INITIAL_DELAY - INTERVAL_DELAY)
return () => clearInterval(interval)
})
答案 3 :(得分：-1)
这是您要实现的目标吗？ useeffect上的空数组告诉它，一旦呈现元素，它将运行此代码
const {useState, useEffect} = React;
// Example stateless functional component
const SFC = props => {
const [value,setvalue] = useState('initial')
const [counter,setcounter] = useState(0)
useEffect(() => {
const timer = setInterval(() => {
setvalue('delayed value')
setcounter(counter+1)
clearInterval(timer)
}, 2000);
}, []);
return(<div>
Value:{value} | counter:{counter}
</div>)
};
// Render it
ReactDOM.render(
<SFC/>,
document.getElementById("react")
);<div id="react"></div>
<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></script>
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