将异步获取的数据传递给子道具 [英] Passing asynchronously acquired data to child props
问题描述
我正在开发一个应用程序,该应用程序可以从远程来源获取一系列新闻,并将其显示在页面上.
I am making an app that gets an array of news items from a remote source and displays them on a page.
我有终结点,可以使用 $.getJSON()
进行成功的呼叫,控制台控制台证明.我将此调用放入了父组件中,因为子组件将需要使用数据.
I have the endpoint, and can make a successful call, proven by console logs, using $.getJSON()
. I placed this call into the parent component, because child components will need to use the data.
但是,当我将此数据传递给子组件时,出现控制台错误:
However, when I pass this data down to a child component, the console error appears:
未捕获的TypeError:无法读取未定义的属性"headline"
这是因为React甚至在将数据传递到组件之前就尝试渲染该组件.这使我认为我应该首先在 componentDidMount
之外的其他地方调用我的Ajax.
This is because React is trying to render the component even before the data has been passed into it. This makes me think I should first be calling my ajax somewhere other than componentDidMount
.
要解决此问题,我在子组件上设置了一个方法,如果该道具存在,则该方法返回标题:
To get around it, I set up a method on the child component that returns the headline if the prop is present:
getHeadline: function () {
if(this.props.newsItems){
return this.props.newsItems.headline
} else {
return null
}
},
感觉好像有点讨厌.有没有更好的方法,还是我的代码中缺少某些内容?
This feels like a bit of a nasty way around it. Is there a better way, or am I missing something in my code?
var BigStory = React.createClass({
getHeadline: function () {
if(this.props.newsItems){
return this.props.newsItems.headline
} else {
return null
}
},
render: function () {
console.log('props:', this.props);
console.log('newsItems:', this.props.newsItems);
return (
<div className="big-story col-xs-12">
<div className="col-sm-5">
<h1>{this.getHeadline()}</h1>
<p>Placeholder text here for now.</p>
<p>time | link</p>
</div>
<div className="col-sm-7">
<img src="http://placehold.it/320x220" alt=""/>
</div>
</div>
);
}
});
var Main = React.createClass({
getInitialState: function () {
return {
newsItems: []
}
},
componentDidMount: function () {
this.getNewsItems();
},
getNewsItems: function () {
$.getJSON('http://www.freecodecamp.com/news/hot', (data) => {
console.log('data sample:', data[0]);
this.setState({newsItems: data})
})
},
render: function () {
return (
<div className="container">
<div className="main-content col-sm-12">
<div className="left-sided-lg-top-otherwise col-lg-8 col-md-12 col-sm-12 col-xs-12">
<BigStory newsItems={this.state.newsItems[0]}/>
</div>
</div>
</div>
);
}
});
推荐答案
我建议让它交给父母来决定当它处于加载"状态并离开 BigStory
时该怎么做.作为一个哑"组件,假定始终将收到有效的 newsItem
.
I would suggest leaving it up to the parent to decide what to do when it is in a "loading" state and leaving BigStory
as a "dumb" component that always renders the same assuming it will always receive a valid newsItem
.
在此示例中,我显示< LoadingComponent/>
,但这可以是您需要的任何内容.概念是 BigStory
不必担心接收无效数据"的极端情况.
In this example, I show a <LoadingComponent />
, but this could be whatever you need it to be. The concept is that BigStory
shouldn't have to worry about edge cases with "receiving invalid data".
var Main = React.createClass({
// ...
render() {
const {newsItems} = this.state;
// You could do this, pass down `loading` explicitly, or maintain in state
const loading = newsItems.length === 0;
return (
<div className="container">
<div className="main-content col-sm-12">
<div className="left-sided-lg-top-otherwise col-lg-8 col-md-12 col-sm-12 col-xs-12">
{loading
? <LoadingComponent />
: <BigStory newsItem={newsItems[0]} />
}
</div>
</div>
</div>
);
}
});
function BigStory(props) {
// Render as usual. This will only be used/rendered w/ a valid
return (
<div className="big-story col-xs-12">
<h1>{props.headline}</h1>
{/* ... */}
</div>
)
}
另一种解决方案(尽管我建议使用类似上述的方法)将始终以相同的方式使用 BigStory
组件,但在没有该组件的情况下为其提供占位符故事"故事已加载.
An alternative solution (although I recommend an approach more like above) would be to always make use of the BigStory
component in the same way, but provide it a "placeholder story" when there are no stories loaded.
const placeholderNewsItem = {
headline: 'Loading...',
/* ... */
};
var Main = React.createClass({
// ...
render() {
const {newsItems} = this.state;
// Conditionally pass BigStory a "placeholder" news item (i.e. with headline = 'Loading...')
const newsItem = newsItems.length === 0
? placeholderNewsItem
: newsItems[0];
return (
<div className="container">
<div className="main-content col-sm-12">
<div className="left-sided-lg-top-otherwise col-lg-8 col-md-12 col-sm-12 col-xs-12">
<BigStory newsItem={newsItem} />
</div>
</div>
</div>
);
}
});
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