React Native ListView - rowHasChanged 不会触发 [英] React Native ListView - rowHasChanged doesn't fire

问题描述

我正在尝试在 React Native 中实现无限滚动.以下是组件的来源:

I am trying to implement an infinite scroll in React Native. Below is the source of the component:

var React = require('react-native');
var server = require('../server');
var Post = require('./Post');
var SwipeRefreshLayoutAndroid = require('./SwipeRefreshLayout');
var backEvent = null;
var lastPostId = "";
var isLoadingMore = false;
var isLoadingTop = false;
var onEndReachedActive = false;

var {
    StyleSheet,
    ListView,
    View,
    Text,
    Image,
    ProgressBarAndroid,
    BackAndroid
} = React;

class Stream extends React.Component {

constructor(props) {
    super(props);
    this.ds = new ListView.DataSource({
        rowHasChanged: (row1, row2) => {
            console.log("rowHasChenged FIRED!!");
            return false;
        }
    });

    this.state = {
        dataSource: this.ds.cloneWithRows(['loader']),
        hasStream: false,
        posts: []
    };

}

componentDidMount() {

    BackAndroid.addEventListener('hardwareBackPress', () => {
        this.props.navigator.jumpBack();
        return true;
    }.bind(this));

    server.getStream('', '', 15).then((res) => {

        lastPostId = res[res.length-1].m._id;

        this.setState({
            posts: res,
            hasStream: true,
            dataSource: this.ds.cloneWithRows(res)
        }, () => onEndReachedActive = true);
    })
}

onRefresh() {
    var posts = this.state.posts;
    var firstPost = posts[0].m._id;

    console.log(this.state.dataSource._rowHasChanged);

    isLoadingTop = true;

    server.getStream('', firstPost, 4000)
        .then(res => {
            console.log(posts.length);
             posts = res.concat(posts);
             console.log(posts.length);
             this.setState({
                dataSource: this.ds.cloneWithRows(posts),
                posts
             }, () => {
                this.swipeRefreshLayout && this.swipeRefreshLayout.finishRefresh();
                isLoadingTop = false;
             });
        }).catch((err) => {
            isLoadingTop = false;
        })

}

onEndReached(event) {

    if(!onEndReachedActive) return;

    if(this.state.loadingMore || this.state.isLoadingTop)return;
    isLoadingMore = true;
    var posts = this.state.posts;
    server.getStream(posts[posts.length-1].m._id, '', 15)
        .then(res => {
            console.log('received posts');
            posts = posts.concat(res);
            lastPostId = posts[posts.length-1].m._id;
            this.setState({
                dataSource: this.ds.cloneWithRows(posts),
                posts
            }, ()=>isLoadingMore = false);
        })
}

renderHeader() {
    return (
        <View style={styles.header}>
            <Text style={styles.headerText}>Header</Text>
        </View> 
    )
}

renderRow(post) {

    if(post === 'loader') {
        return (
            <ProgressBarAndroid 
                styleAttr="Large" 
                style={styles.spinnerBottom}/>
        )
    }

    let hasLoader = post.m._id === lastPostId;

    let loader = hasLoader ? 
        <ProgressBarAndroid 
            styleAttr="Large" 
            style={styles.spinnerBottom}/> : null;

    return (
        <View>
            <Post 
                post={post}/>
            {loader}
        </View> 
    )
}

render() {


    return (
                <ListView
                    style={styles.mainContainer}
                    dataSource={this.state.dataSource}
                    renderRow={this.renderRow.bind(this)}
                    onEndReached={this.onEndReached.bind(this)}
                    onEndReachedThreshold={1}
                    pageSize={15} />
    );
}
}

问题是，每当我追加(或添加)新数据时，DataSource 的 rowHasChanged 方法不会触发.它只是重新渲染每一行，即使没有任何变化(新数据除外).知道为什么绕过该方法吗?

The problem is that whenever I append (or prepend) new data, the rowHasChanged method of the DataSource doesn't fire. It just re-renders every row, even tho nothing has changed (except the new data). Any idea why the method is bypassed?

推荐答案

将函数传递给 setState 以避免竞争条件

Pass a function to setState to avoid race conditions

我刚刚想通了.如果您遇到同样的问题，请检查您使用新的 dataSource 更改状态的点.我的是这样的:

I just figured it out. If you are having the same issue, check the point at which you change your state with the new dataSource. Mine was like this:

this.setState({
    dataSource: this.ds.cloneWithRows(posts)
});

相反，您应该始终使用先前状态中的 dataSource，如下所示:

Instead you should always use the dataSource from the previous state, like this:

this.setState(state => ({
    dataSource: state.dataSource.cloneWithRows(posts)
}))

干杯！

这篇关于React Native ListView - rowHasChanged 不会触发的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！