Reactjs 如何在react with hooks中通过切换功能设置和清理间隔?
我正在尝试构建一个计时器开关,该开关由一个带有函数handleToggle的按钮触发,如下所示:Reactjs 如何在react with hooks中通过切换功能设置和清理间隔?,reactjs,setinterval,react-hooks,clearinterval,Reactjs,Setinterval,React Hooks,Clearinterval,我正在尝试构建一个计时器开关,该开关由一个带有函数handleToggle的按钮触发,如下所示: const handleToggle = () => { let timer = () => setInterval(() => { dispatch({ type: "COUNT", payload: Date.now() - startTime }); }, 100); const startTime = Date.now() - AppSt
const handleToggle = () => {
let timer = () => setInterval(() => {
dispatch({ type: "COUNT", payload: Date.now() - startTime });
}, 100);
const startTime = Date.now() - AppState.runningTime;
if (AppState.countingStarted) {
dispatch({
type: "COUNTING_STARTED",
payload: false
});
clearInterval(timer());
} else {
timer()
dispatch({ type: "COUNTING_STARTED", payload: true });
}
};
COUNTING_STARTED是一个调度函数,用于切换AppState.countingStarted
我正在努力停止计时器,如何清除计时器间隔?
我试过:
但是没有区别…在您的示例中,对
intervalId
的引用在函数执行结束时丢失
您应该使用实例变量来存储intervalId。如果您有类
组件,则可以使用以下代码:
handleToggle = () => {
// clear the interval, no matter the value of AppState.countingStarted
// this prevent from recreating the interval multiple times
clearInterval(this.timerId);
if (AppState.countingStarted) {
dispatch({type: "COUNTING_STARTED",payload: false});
} else {
// store the timer id in an instance variable
this.timerId = setInterval(() => {
dispatch({ type: "COUNT", payload: Date.now() - startTime });
}, 100);
dispatch({ type: "COUNTING_STARTED", payload: true });
}
如果您在函数
组件中,则可以使用来获得相同的行为:
const timerIdRef = useRef(null);
const handleToggle = () => {
clearInterval(timerIdRef.current);
if (AppState.countingStarted) {
dispatch({type: "COUNTING_STARTED",payload: false});
} else {
// store the interval id into the current property
timerIdRef.current = setInterval(() => {
dispatch({ type: "COUNT", payload: Date.now() - startTime });
}, 100);
dispatch({ type: "COUNTING_STARTED", payload: true });
}
有两件事:传递给
clearInterval
的必须是setInterval
的返回值;在第一个示例中,您将自己的函数传递给它。第二个示例有此权利,但您正在将计时器
(调用setInterval
的结果)存储在toggle函数的范围内,这意味着一旦函数完成,您将丢失对它的引用;下次调用函数时(例如停止函数),您需要重新定义计时器
,这不是您想要的
您所需要的只是将计时器
变量保持在它将持续存在的范围内。例如:
let timer = null;
const handleToggle = () => {
if (AppState.countingStarted) {
dispatch({
type: "COUNTING_STARTED",
payload: false
});
clearInterval(timer);
} else {
timer = setInterval(() => {
dispatch({ type: "COUNT", payload: Date.now() - startTime });
}, 100);
const startTime = Date.now() - AppState.runningTime;
dispatch({ type: "COUNTING_STARTED", payload: true });
}
};
此函数可以多次调用;
timer
变量将一直存在。您再次在handleToggle
中初始化了计时器。您可以使用带有钩子的setInterval
查看Dan Abramov的博客帖子:
let timer = null;
const handleToggle = () => {
if (AppState.countingStarted) {
dispatch({
type: "COUNTING_STARTED",
payload: false
});
clearInterval(timer);
} else {
timer = setInterval(() => {
dispatch({ type: "COUNT", payload: Date.now() - startTime });
}, 100);
const startTime = Date.now() - AppState.runningTime;
dispatch({ type: "COUNTING_STARTED", payload: true });
}
};