我正在尝试为React Native内置的iOS应用加载启动画面。我试图通过类状态然后使用setTimeout函数完成此操作,如下所示:
I'm trying to load a splash screen for an iOS app built in React Native. I'm trying to accomplish this through class states and then a setTimeout function as follows:
class CowtanApp extends Component { constructor(props){ super(props); this.state = { timePassed: false }; } render() { setTimeout(function(){this.setState({timePassed: true})}, 1000); if (!this.state.timePassed){ return <LoadingPage/>; }else{ return ( <NavigatorIOS style = {styles.container} initialRoute = {{ component: LoginPage, title: 'Sign In', }}/> ); } } }加载页面适用于第二,然后我猜当setTimeout尝试将状态更改为true时,我的程序崩溃:'undefined不是对象(评估this.setState)'。我已经花了几个小时,有关如何修复它的任何想法?
The loading page works for a second, and then I guess when setTimeout tries to change the state to true, my program crashes: 'undefined is not an object (evaluating this.setState)'. I've been going at this for a couple of hours, any ideas on how to fix it?
推荐答案经典的javascript错误。
Classic javascript mistake.
setTimeout(function(){this.setState({timePassed: true})}, 1000)当 setTimeout 运行 this.setState ,此不再是 CowtanApp ,但窗口。如果使用 => 表示法定义函数,es6将自动绑定此。
When setTimeout runs this.setState, this is no longer CowtanApp, but window. If you define the function with the => notation, es6 will auto-bind this.
setTimeout(() => {this.setState({timePassed: true})}, 1000)或者,你可以使用让你的在你的 render ,然后切换你的引用以使用局部变量。
Alternatively, you could use a let that = this; at the top of your render, then switch your references to use the local variable.
render() { let that = this; setTimeout(function(){that.setState({timePassed: true})}, 1000);更多推荐
React Native中的setTimeout
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