城市列表選擇是很多app共有的功能，比如典型的美圖app。那麼對於React Native怎麼實現呢？

要實現上面的效果，首先需要對介面的組成簡單分析，介面的資料主要由當前城市，歷史訪問城市和熱門城市組成，所以我們在提供Json資料的時候就需要將資料分為至少3部分。

const ALL_CITY_LIST = DATA_JSON.allCityList;
const HOT_CITY_LIST = DATA_JSON.hotCityList;
const LAST_VISIT_CITY_LIST = DATA_JSON.lastVisitCityList;

而要實現字母索引功能，我們需要自定義一個控制元件，實現和資料的繫結關係，自定義元件程式碼如下：
CityIndexListView.js

'use strict';
import React, {Component} from 'react';
import {
    StyleSheet,
    View,
    Text,
    TouchableOpacity,
    ListView,
    Dimensions,
} from 'react-native';

import Toast, {DURATION} from './ToastUtil'

const SECTIONHEIGHT = 30;
const ROWHEIGHT = 40;
const ROWHEIGHT_BOX = 40;
var totalheight = []; //
 
每個字母對應的城市和字母的總高度

const {width, height} = Dimensions.get('window');

var that;

const key_now = '當前';
const key_last_visit = '最近';
const key_hot = '熱門';

export default class CityIndexListView extends Component {

    constructor(props) {
        super(props);

        var getSectionData = (dataBlob, sectionID)
 
 => {
            return sectionID;
        };
        var getRowData = (dataBlob, sectionID, rowID) => {
            return dataBlob[sectionID][rowID];
        };

        let ALL_CITY_LIST = this.props.allCityList;
        let CURRENT_CITY_LIST = this.props.nowCityList;
        let LAST_VISIT_CITY_LIST = this.props.lastVisitCityList;
        let HOT_CITY_LIST = this.props.hotCityList;

        let letterList = this._getSortLetters(ALL_CITY_LIST);

        let dataBlob = {};
        dataBlob[key_now] = CURRENT_CITY_LIST;
        dataBlob[key_last_visit] = LAST_VISIT_CITY_LIST;
        dataBlob[key_hot] = HOT_CITY_LIST;

        ALL_CITY_LIST.map(cityJson => {
            let key = cityJson.sortLetters.toUpperCase();

            if (dataBlob[key]) {
                let subList = dataBlob[key];
                subList.push(cityJson);
            } else {
                let subList = [];
                subList.push(cityJson);
                dataBlob[key] = subList;
            }
        });

        let sectionIDs = Object.keys(dataBlob);
        let rowIDs = sectionIDs.map(sectionID => {
            let thisRow = [];
            let count = dataBlob[sectionID].length;
            for (let ii = 0; ii < count; ii++) {
                thisRow.push(ii);
            }

            let eachheight = SECTIONHEIGHT + ROWHEIGHT * thisRow.length;
            if (sectionID === key_hot || sectionID === key_now || sectionID === key_last_visit) {
                let rowNum = (thisRow.length % 3 === 0)
                    ? (thisRow.length / 3)
                    : parseInt(thisRow.length / 3) + 1;

                console.log('sectionIDs===>' + sectionIDs + ", rowNum=====>" + rowNum);

                eachheight = SECTIONHEIGHT + ROWHEIGHT_BOX * rowNum;
            }

            totalheight.push(eachheight);

            return thisRow;
        });


        let ds = new ListView.DataSource({
            getRowData: getRowData,
            getSectionHeaderData: getSectionData,
            rowHasChanged: (row1, row2) => row1 !== row2,
            sectionHeaderHasChanged: (s1, s2) => s1 !== s2
        });

        this.state = {
            dataSource: ds.cloneWithRowsAndSections(dataBlob, sectionIDs, rowIDs),
            letters: sectionIDs
        };

        that = this;
    }

    _getSortLetters(dataList) {
        let list = [];

        for (let j = 0; j < dataList.length; j++) {
            let sortLetters = dataList[j].sortLetters.toUpperCase();

            let exist = false;
            for (let xx = 0; xx < list.length; xx++) {
                if (list[xx] === sortLetters) {
                    exist = true;
                }
                if (exist) {
                    break;
                }
            }
            if (!exist) {
                list.push(sortLetters);
            }
        }

        return list;
    }

    _cityNameClick(cityJson) {
        // alert('選擇了城市====》' + cityJson.id + '#####' + cityJson.name);
        this.props.onSelectCity(cityJson);
    }

    _scrollTo(index, letter) {
        this.refs.toast.close();
        let position = 0;
        for (let i = 0; i < index; i++) {
            position += totalheight[i]
        }
        this._listView.scrollTo({y: position});
        this.refs.toast.show(letter, DURATION.LENGTH_SHORT);
    }

    _renderRightLetters(letter, index) {
        return (
            <TouchableOpacity key={'letter_idx_' + index} activeOpacity={0.6} onPress={() => {
                this._scrollTo(index, letter)
            }}>
                <View style={styles.letter}>
                    <Text style={styles.letterText}>{letter}</Text>
                </View>
            </TouchableOpacity>
        );
    }

    _renderListBox(cityJson, rowId) {
        return (
            <TouchableOpacity key={'list_item_' + cityJson.id} style={styles.rowViewBox} onPress={() => {
                that._cityNameClick(cityJson)
            }}>
                <View style={styles.rowdataBox}>
                    <Text style={styles.rowDataTextBox}>{cityJson.name}</Text>
                </View>
            </TouchableOpacity>
        );
    }

    _renderListRow(cityJson, rowId) {
        console.log('rowId===>' + rowId + ", cityJson====>" + JSON.stringify(cityJson));
        if (rowId === key_now || rowId === key_hot || rowId === key_last_visit) {
            return that._renderListBox(cityJson, rowId);
        }

        return (
            <TouchableOpacity key={'list_item_' + cityJson.id} style={styles.rowView} onPress={() => {
                that._cityNameClick(cityJson)
            }}>
                <View style={styles.rowdata}>
                    <Text style={styles.rowdatatext}>{cityJson.name}</Text>
                </View>
            </TouchableOpacity>
        )
    }

    _renderListSectionHeader(sectionData, sectionID) {
        return (
            <View style={styles.sectionView}>
                <Text style={styles.sectionText}>
                    {sectionData}
                </Text>
            </View>
        );
    }

    render() {
        return (
            <View style={styles.container}>
                <View style={styles.listContainner}>
                    <ListView ref={listView => this._listView = listView}
                              contentContainerStyle={styles.contentContainer} dataSource={this.state.dataSource}
                              renderRow={this._renderListRow} renderSectionHeader={this._renderListSectionHeader}
                              enableEmptySections={true} initialListSize={500}/>
                    <View style={styles.letters}>
                        {this.state.letters.map((letter, index) => this._renderRightLetters(letter, index))}
                    </View>
                </View>
                <Toast ref="toast" position='top' positionValue={200} fadeInDuration={750} fadeOutDuration={1000}
                       opacity={0.8}/>
            </View>
        )
    }
}

const styles = StyleSheet.create({
    container: {
        // paddingTop: 50,
        flex: 1,
        flexDirection: 'column',
        backgroundColor: '#F4F4F4',
    },
    listContainner: {
        height: Dimensions.get('window').height,
        marginBottom: 10
    },
    contentContainer: {
        flexDirection: 'row',
        width: width,
        backgroundColor: 'white',
        justifyContent: 'flex-start',
        flexWrap: 'wrap'
    },
    letters: {
        position: 'absolute',
        height: height,
        top: 0,
        bottom: 0,
        right: 10,
        backgroundColor: 'transparent',
        // justifyContent: 'flex-start',
        // alignItems: 'flex-start'
        alignItems: 'center',
        justifyContent: 'center'
    },
    letter: {
        height: height * 4 / 100,
        width: width * 4 / 50,
        justifyContent: 'center',
        alignItems: 'center'
    },
    letterText: {
        textAlign: 'center',
        fontSize: height * 1.1 / 50,
        color: '#e75404'
    },
    sectionView: {
        paddingTop: 5,
        paddingBottom: 5,
        height: 30,
        paddingLeft: 10,
        width: width,
        backgroundColor: '#F4F4F4'
    },
    sectionText: {
        color: '#e75404',
        fontWeight: 'bold'
    },
    rowView: {
        height: ROWHEIGHT,
        paddingLeft: 10,
        paddingRight: 10,
        borderBottomColor: '#F4F4F4',
        borderBottomWidth: 0.5
    },
    rowdata: {
        paddingTop: 10,
        paddingBottom: 2
    },

    rowdatatext: {
        color: 'gray',
        width: width
    },

    rowViewBox: {
        height: ROWHEIGHT_BOX,
        width: (width - 30) / 3,
        flexDirection: 'row',
        backgroundColor: '#ffffff'
    },
    rowdataBox: {
        borderWidth: 1,
        borderColor: '#DBDBDB',
        marginTop: 5,
        marginBottom: 5,
        paddingBottom: 2,
        marginLeft: 10,
        marginRight: 10,
        flex: 1,
        justifyContent: 'center',
        alignItems: 'center'
    },
    rowDataTextBox: {
        marginTop: 5,
        flex: 1,
        height: 20
    }

});

然後在頭部還需要實現一個搜尋框。
SearchBox.js

'use strict';
import React, {Component} from 'react';
import {
    View,
    TextInput,
    StyleSheet,
    Platform,
} from 'react-native';

export default class SearchBox extends Component {
    constructor(props) {
        super(props);
        this.state = {
            value: ''
        };

    }

    onEndEditingKeyword(vv) {
        console.log(vv);
    }

    onChanegeTextKeyword(vv) {
        console.log('onChanegeTextKeyword', vv);

        this.setState({value: vv});
        this.props.onChanegeTextKeyword(vv);
    }

    render() {
        return (
            <View style={styles.container}>
                <View style={styles.inputBox}>
                    <View style={styles.inputIcon}>
                    </View>
                    <TextInput ref="keyword" autoCapitalize="none" value={this.props.keyword}
                               onChangeText={this.onChanegeTextKeyword.bind(this)} returnKeyType="search" maxLength={20}
                               style={styles.inputText} underlineColorAndroid="transparent"
                               placeholder={'輸入城市名或拼音查詢'}/>
                </View>
            </View>
        )
    }
}

const styles = StyleSheet.create({
    container: {
        marginTop: 5,
        marginBottom: 5,
        backgroundColor: '#ffffff',
        flexDirection: 'row',
        height: Platform.OS === 'ios'
            ? 35
            : 45,
        borderBottomWidth: StyleSheet.hairlineWidth,
        borderBottomColor: '#cdcdcd',
        paddingBottom: 5
    },
    inputBox: {
        height: Platform.OS === 'ios'
            ? 30
            : 40,
        marginLeft: 5,
        marginRight: 5,
        flex: 1,
        flexDirection: 'row',
        backgroundColor: '#E6E7E8'
    },
    inputIcon: {
        margin: Platform.OS === 'ios'
            ? 5
            : 10
    },
    inputText: {
        alignSelf: 'flex-end',
        marginTop: Platform.OS === 'ios'
            ? 0
            : 0,
        flex: 1,
        height: Platform.OS === 'ios'
            ? 30
            : 40,
        marginLeft: 2,
        marginRight: 5,
        fontSize: 12,
        lineHeight: 30,
        textAlignVertical: 'bottom',
        textDecorationLine: 'none'
    }
});