我只是在用户向下滚过标题时尝试制作页脚横幅,并在用户向上滚动到顶部时隐藏它.我对如何实现这个的想法是在页面的顶部组件中为scroll事件添加一个事件监听器.这是我目前的代码.但它不起作用:
componentDidMount() {
this.nv.addEventListener('scroll', this.handleScroll);
}
handleScroll(e) {
if(window.pageYOffset > 50 && window.pageYOffset < 900) {
console.log('scrolled');
this.setState({
showBanner: true,
});
} else {
this.setState({
showBanner: false,
});
}
}
顶级组件的渲染方法:
render() {
return (
<div ref={elem => this.nv = elem}>
<Header/>
<Body
userInfo={this.props.userInfo}
history={this.props.history}
/>
{
this.state.showBanner && <Banner/>
|| null
}
</div>
)
}
我没有看到任何日志,setState滚动时显然没有调用.
关于如何实现预期目标的任何建议？
*UPDATE*
更改componentDidMount为在窗口上添加事件监听器,现在它正在工作.
componentDidMount() {
window.addEventListener('scroll', this.handleScroll);
}
我正在使用react-native-fetch-blob来下载mp3文件,然后再播放它们.问题是RNFetchBlob.fs.dirs.DocumentDir当我关闭应用程序并重新启动时,实际的更改路径,这意味着我无法使用下载文件后立即存储的绝对文件路径,在下次运行应用程序时检索文件.
这是我下载和存储文件路径的代码:
export function downloadAudio(urlArray) { //download every section in the urlArray
return (dispatch) => {
Promise.all(urlArray.map(section => {
dispatch(startDownload(section.section_id))
console.log('download start for id = ',section.section_id ) //start download
return RNFetchBlob
.config({
path: RNFetchBlob.fs.dirs.DocumentDir + '/courseSections/' + section.section_id + '.mp3',
appendExt: 'mp3'
})
.fetch('GET', section.section_url, {
'Cache-Control': 'no-store'
})
.progress({ count: 10 }, (received, total) => {
console.log(`progress for section ${section.section_id}: `, Math.floor(received/total*100), '%')
dispatch(downloadProgress({id: section.section_id, progress: Math.floor(received/total*100)/100}))
})
.then(res => {
console.log(`section ${section.section_id} is saved to: `, …