javascript - React Hooks useState useEffect 幻灯片
问题描述
我正在尝试通过将以下数据传递给Slide.js
via props 来制作幻灯片应用程序。
const SLIDES = [
{
title: "Today's workout plan",
text: "We're gonna do 3 fundamental exercises."
},
{
title: "First, 10 push-ups",
text: "Do 10 reps. Remember about full range of motion. Don't rush."
},
{
title: "Next, 20 squats",
text: "Squats are important. Remember to keep your back straight."
},
{
title: "Finally, 15 sit-ups",
text: "Slightly bend your knees. Remember about full range of motion."
},
{
title: "Great job!",
text: "You made it, have a nice day and see you next time!"
}
];
我的子组件Slide.js
具有以下代码
import React, { useState, useEffect } from "react";
function Slides({ slides }) {
const [slideShow, setSlide] = useState(slides);
useEffect(() => {
setSlide(slideShow[0]);
console.log("slides", slideShow[0]);
}, []);
return (
<div>
<div id="navigation" className="text-center">
<button data-testid="button-restart" className="small outlined">
Restart
</button>
<button data-testid="button-prev" className="small">
Prev
</button>
<button data-testid="button-next" className="small">
Next
</button>
</div>
{slideShow.map((slide, i) => (
<div id={i} className="card text-center">
<h1 data-testid="title">{slide.title}</h1>
<p data-testid="text">{slide.text}</p>
</div>
))}
</div>
);
}
export default Slides;
我认为 usingsetSlide(slideShow[0])
只会在应用程序最初加载后呈现对象数组中的第一项。但我明白了
TypeError: slideShow.map is not a function
但是当console.log("slides", slideShow[0])
我输出
slides {title: "Today's workout plan", text: "We're gonna do 3 fundamental exercises."}
如果我将代码更改为
setSlide(slideShow.slice(0, 1));
该应用程序仅显示数组中的第一个对象,但如果 I console.log("slides", slideShow)
,即使我认为我应该收到切片版本,我也会得到整个对象数组。
我的map
函数是否没有引用slideShow[0]
错误的发生?
解决方案
这里的问题是setSlide(slideShow[0])
。最初,状态是用一个名为 的数组初始化的slides
。但是在useEffect
那个状态下,正在用一个对象进行更新。所以,现在slideShow
不再是一个,array
而是一个object
。因此object.map
正在破坏应用程序。
useEffect(() => {
setSlide(slideShow[0]);
console.log("slides", slideShow[0]);
}, []);
以下是您正在寻找的操作类型的示例。而不是存储slides
在我刚刚添加index
项目的状态中state
并相应地更新它。
const SLIDES = [{title:"Today's workout plan",text:"We're gonna do 3 fundamental exercises."},{title:"First, 10 push-ups",text:"Do 10 reps. Remember about full range of motion. Don't rush."},{title:"Next, 20 squats",text:"Squats are important. Remember to keep your back straight."},{title:"Finally, 15 sit-ups",text:"Slightly bend your knees. Remember about full range of motion."},{title:"Great job!",text:"You made it, have a nice day and see you next time!"}];
const { useState, useEffect } = React;
function Slides({ slides }) {
const [selectedIndex, setSelectedIndex] = useState(0);
const previous = () => {
if(selectedIndex !== 0) {
setSelectedIndex(index => index-1);
}
}
const next = () => {
if(selectedIndex !== slides.length - 1) {
setSelectedIndex(index => index+1);
}
}
const restart = () => {
setSelectedIndex(0);
}
return (
<div>
<div id="navigation" className="text-center">
<button data-testid="button-restart" className="small outlined" onClick={restart}>
Restart
</button>
<button data-testid="button-prev" className="small" onClick={previous}>
Prev
</button>
<button data-testid="button-next" className="small" onClick={next}>
Next
</button>
</div>
<div className="card text-center">
<h1 data-testid="title">{slides[selectedIndex].title}</h1>
<p data-testid="text">{slides[selectedIndex].text}</p>
</div>
</div>
);
}
ReactDOM.render(<Slides slides={SLIDES}/>, document.getElementById("react"));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.0/umd/react-dom.production.min.js"></script>
<div id="react"></div>
注意:在这里,对于所有三个操作,我们可以只使用一个函数,为了简单起见,我创建了三个不同的函数来更新幻灯片索引。
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