React Native ListView的滚动scrollTo

1.通过onLayout快速的获得一个view的位置、宽、高

class TestView extends Component {
    // 构造
    constructor(props) {
        super(props);

        this.state = {
            x: 0,
            y: 0,
            width: 0,
            height: 0
        }
    }

    measureView(event) {
        console.log('event peroperties: ', event);
        this.setState({
            x: event.nativeEvent.layout.x,
            y: event.nativeEvent.layout.y,
            width: event.nativeEvent.layout.width,
            height: event.nativeEvent.layout.height
        })
    }

    changeHeight() {
        this.setState({
            viewHeight: 200
        })
    }

    render(){
        return (
            <View >
                <View onLayout={(event) => this.measureView(event)}  style={{height:this.state.viewHeight, marginTop:120, backgroundColor: 'orange'}}>
                    <Text >The outer view of this text is being measured!</Text>
                    <Text>x: {this.state.x}</Text>
                    <Text>y: {this.state.y}</Text>
                    <Text>width: {this.state.width}</Text>
                    <Text>height: {this.state.height}</Text>
                </View>

                <TouchableHighlight style={{flexDirection:'row', alignItems: 'center', justifyContent: 'center', padding:15, backgroundColor: '#ddd', marginTop:10}} onPress={() => this.changeHeight() }>
                    <Text style={{fontSize:18}}>Change height of container</Text>
                </TouchableHighlight>
            </View>
        );
    }
}

2. 用ScrollView+Items来实现滚动到ScrollView的底部

class TestView extends Component {
    // 构造
    constructor(props) {
        super(props);
        
        this.state = {
            listHeight: 0,
            scrollViewHeight: 0
        }
    }

    componentDidUpdate(){
        this.scrollToBottom()
    }
    scrollToBottom(){
        const bottomOfList =  this.state.listHeight - this.state.scrollViewHeight
        console.log('scrollToBottom');
        this.scrollView.scrollTo({ y: bottomOfList })
    }

    renderRow(message, index){
        return  <Text key={index}> {message} </Text>
    }

    render() {
        return (
            <View style={{flex: 1}}>
                <View style={{height: 200, backgroundColor: 'red'}}></View>
                <ScrollView
                    keyboardDismissMode="on-drag"
                    onContentSizeChange={ (contentWidth, contentHeight) => {
                        this.setState({listHeight: contentHeight })
                    }}
                    onLayout={ (e) => {
                        const height = e.nativeEvent.layout.height

                        console.log("------------scollview height: " + height)
                        this.setState({scrollViewHeight: height })
                    }}
                    ref={ (ref) => this.scrollView = ref }>
                    {this.props.messages.map(  message =>  this.renderRow(message) )}
                </ScrollView>
            </View>
        )
    }
}

滚动的距离=listHeight - viewHeight=列表内容高度 - 视口高度

3.利用footer来定位ListView底部坐标

class TestView extends Component {
    // 构造
    constructor(props) {
        super(props);

        this.ds = new ListView.DataSource({rowHasChanged: (r1, r2) => r1 !== r2})

        this.data = []
        for (let i = 0; i < 1000; ++i) {
            this.data.push(i)
        }
        this.state = {
            listHeight: 0,
            dataSource: this.ds.cloneWithRows(this.data)
        }
    }

    componentDidUpdate() {
        this.scrollToBottom()
    }

    scrollToBottom() {
        if (this.listHeight && this.footerY && this.footerY > this.listHeight) {
            let delta = this.footerY - this.listHeight
            let scrollResponder = this.listView.getScrollResponder()
            scrollResponder.scrollTo({y: delta, animated: true})
        }
    }

    renderRow(rowData, sectionID, rowID, highlightRow) {
        console.log("renderRow:" + utils.toString(rowData))
        return <Text key={rowData}>{rowData}</Text>
    }

    render() {
        return (
            <View style={{flex: 1}}>
                <Text style={{height: 100, backgroundColor: 'green'}} onPress={() => this.onClicked()}> ClickedMe </Text>
                <ListView
                    ref={(listview) => this.listView = listview}
                    initialListSize={30}
                    pageSize={30}
                    onLayout={
                        e => {
                            console.log("----------------ListView onLayout:" + e.nativeEvent.layout.height)
                            this.listHeight = e.nativeEvent.layout.height
                        }
                    }
                    dataSource={this.state.dataSource}
                    renderRow={(...args) => this.renderRow(...args)}
                    renderFooter = {() => {
                        return (
                            <View onLayout={ (e) => {
                                console.log("--------------------render footer" + e.nativeEvent.layout.y)
                                this.footerY = e.nativeEvent.layout.y}
                            }></View>
                        )
                    }}
                >

                </ListView>
            </View>
        )
    }

    onClicked() {
        this.scrollToBottom()
    }
}

缺点:

• renderFooter需要设置页刷新行数等优化数据，否则效率低，会不断调用renderfooter
• ListView数据大的时候，不会一次性渲染完所有数据，所以调用scrollToBottom,可能只滚动到中间部分
  eg.1000行数据，每次渲染50行，renderFooter每隔50行计算一次footer坐标y，每次定位底部坐标都是 50H、100H、150H...950H、1000H
  也就是说，除非一次性渲染完所有的数据，否则无法直接滚动到底部