React Native仿美团下拉菜单

在很多产品中都会涉及到下拉菜单选择功能，用的最好的当属美团了，其效果如下：
这里写图片描述

要实现上面的效果，在原生中比较好做，直接使用PopWindow组件即可。如果使用React Native开发上面的效果，需要注意几个问题：
1、在下拉的时候有动画过度效果；
2、下拉菜单出现后点击菜单项，菜单项可选择，并触发对应的事件；
3、下拉菜单中的项目可以配置；

要实现弹框效果，我们马上回想到使用Model组件，而要绘制打钩图标和下拉三角，我们首先想到使用ART实现，当然选择使用图标也是可以的。例如使用ART绘制对勾的代码如下：

const Check = ()=>{
  return (
     <Surface
        width={18}
        height={12}
        >
        <Group scale={0.03}>
            <Shape
                fill={COLOR_HIGH}
                d={`M494,52c-13-13-33-13-46,0L176,324L62,211c-13-13-33-13-46,0s-13,33,0,46l137,136c6,6,15,10,23,10s17-4,23-10L494,99
      C507,86,507,65,494,52z`}
            />
        </Group>
      </Surface>
  );
}

下拉动画的实现上，需要使用Animated。例如，背景颜色变化需要使用Animated.timing。

this.state.fadeInOpacity,               
 {
   toValue: value,                 
   duration : 250, 
 }

运行效果：

这里写图片描述

本示例设计三个文件：导航栏FoodActionBar.js，下拉弹框TopMenu.js和文件主类FoodView.js。
FoodActionBar.js

/**
 * https://github.com/facebook/react-native
 * @flow 首页的标题栏
 */
import React, {Component} from 'react';
import {Platform, View, Dimensions, Text, StyleSheet, TouchableOpacity, Image} from 'react-native';
import px2dp from '../util/Utils'
const isIOS = Platform.OS == "ios"
const {width, height} = Dimensions.get('window')
const headH = px2dp(isIOS ? 64 : 44)
export default  class FoodActionBar extends Component {
    constructor(props) {
        super(props);
        this.state = {
            showPop: false,
        }
    }
    renderHeader() {
        return (
            <View style={styles.headerStyle}>
                <TouchableOpacity style={styles.action} >
                    <Image style={styles.scanIcon}/>
                </TouchableOpacity>
                <TouchableOpacity style={styles.searchBar}>
                    <Image source={require('../images/ic_search.png')} style={styles.iconStyle}/>
                    <Text style={{fontSize: 13, color: "#666", marginLeft: 5}}>输入商家名、品类和商圈</Text>
                </TouchableOpacity>
                <TouchableOpacity style={styles.action} onPress={() => { this.setState({ showPop: !this.state.showPop }) }}>
                    <Image style={styles.scanIcon}
                           source={require('../images/icon_address.png')}/>
                </TouchableOpacity>
            </View>
        )
    }
    render() {
        return (
            <View>
                {this.renderHeader()}
            </View>
        );
    }
}
const styles = StyleSheet.create({
    headerStyle: {
        backgroundColor: "#ffffff",
        height: headH,
        paddingTop: px2dp(isIOS ? 20 : 0),
        flexDirection: 'row',
        alignItems: 'center',
    },
    searchBar: {
        flex:1,
        height: 30,
        borderRadius: 19,
        backgroundColor:'#e9e9e9',
        marginLeft: 10,
        flexDirection: 'row',
        justifyContent: 'flex-start',
        alignItems: 'center',
        alignSelf: 'center',
        paddingLeft: 10,
    },
    text: {
        fontSize: 16,
        color: '#ffffff',
        justifyContent: 'center',
    },
    iconStyle: {
        width: 22,
        height: 22,
    },
    action: {
        flexDirection: 'row',
        justifyContent: 'center',
        alignItems: 'center',
        marginLeft:10,
        marginRight:10
    },
    scanIcon: {
        width: 28,
        height: 28,
        alignItems: 'center',
    },
    scanText: {
        fontSize: 14,
        color: '#ffffff',
        justifyContent: 'center',
        alignItems: 'center',
    },
});

TopMenu.js

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */
import React, {Component} from 'react';
import {
    AppRegistry,
    StyleSheet,
    Animated,
    ScrollView,
    Dimensions,
    PixelRatio,
    Text,
    TouchableWithoutFeedback,
    TouchableHighlight,
    ART,
    View
} from 'react-native';
const {Surface, Shape, Path, Group} = ART;
const {width, height} = Dimensions.get('window');
const T_WIDTH = 7;
const T_HEIGHT = 4;
const COLOR_HIGH = '#00bea9';
const COLOR_NORMAL = '#6c6c6c';
const LINE = 1 / PixelRatio.get();
class Triangle extends React.Component {
    render() {
        var path;
        var fill;
        if (this.props.selected) {
            fill = COLOR_HIGH;
            path = new Path()
                .moveTo(T_WIDTH / 2, 0)
                .lineTo(0, T_HEIGHT)
                .lineTo(T_WIDTH, T_HEIGHT)
                .close();
        } else {
            fill = COLOR_NORMAL;
            path = new Path()
                .moveTo(0, 0)
                .lineTo(T_WIDTH, 0)
                .lineTo(T_WIDTH / 2, T_HEIGHT)
                .close();
        }
        return (
            <Surface width={T_WIDTH} height={T_HEIGHT}>
                <Shape d={path} stroke="#00000000" fill={fill} strokeWidth={0}/>
            </Surface>
        )
    }
}
const TopMenuItem = (props) => {
    const onPress = () => {
        props.onSelect(props.index);
    }
    return (
        <TouchableWithoutFeedback onPress={onPress}>
            <View style={styles.item}>
                <Text style={props.selected ? styles.menuTextHigh : styles.menuText}>{props.label}</Text>
                <Triangle selected={props.selected}/>
            </View>
        </TouchableWithoutFeedback>
    );
};
const Subtitle = (props) => {
    let textStyle = props.selected ?
        [styles.tableItemText, styles.highlight, styles.marginHigh] :
        [styles.tableItemText, styles.margin];
    let rightTextStyle = props.selected ? [styles.tableItemText, styles.highlight] : styles.tableItemText;
    let onPress = () => {
        props.onSelectMenu(props.index, props.subindex, props.data);
    }
    return (
        <TouchableHighlight onPress={onPress} underlayColor="#f5f5f5">
            <View style={styles.tableItem}>
                <View style={styles.row}>
                    {props.selected && <Check />}
                    <Text style={textStyle}>{props.data.title}</Text>
                </View>
                <Text style={rightTextStyle}>{props.data.subtitle}</Text>
            </View>
        </TouchableHighlight>
    );
};
const Title = (props) => {
    let textStyle = props.selected ?
        [styles.tableItemText, styles.highlight, styles.marginHigh] :
        [styles.tableItemText, styles.margin];
    let rightTextStyle = props.selected ? [styles.tableItemText, styles.highlight] : styles.tableItemText;
    let onPress = () => {
        props.onSelectMenu(props.index, props.subindex, props.data);
    }
    return (
        <TouchableHighlight onPress={onPress} underlayColor="#f5f5f5">
            <View style={styles.titleItem}>
                {props.selected && <Check />}
                <Text style={textStyle}>{props.data.title}</Text>
            </View>
        </TouchableHighlight>
    );
};
const Check = () => {
    return (
        <Surface
            width={18}
            height={12}
        >
            <Group scale={0.03}>
                <Shape
                    fill={COLOR_HIGH}
                    d={`M494,52c-13-13-33-13-46,0L176,324L62,211c-13-13-33-13-46,0s-13,33,0,46l137,136c6,6,15,10,23,10s17-4,23-10L494,99
      C507,86,507,65,494,52z`}
                />
            </Group>
        </Surface>
    );
}
export default class TopMenu extends Component {
    constructor(props) {
        super(props);
        let array = props.config;
        let top = [];
        let maxHeight = [];
        let subselected = [];
        let height = [];
        //最大高度
        var max = parseInt((height - 80) * 0.8 / 43);
        for (let i = 0, c = array.length; i < c; ++i) {
            let item = array[i];
            top[i] = item.data[item.selectedIndex].title;
            maxHeight[i] = Math.min(item.data.length, max) * 43;
            subselected[i] = item.selectedIndex;
            height[i] = new Animated.Value(0);
        }
        //分析数据
        this.state = {
            top: top,
            maxHeight: maxHeight,
            subselected: subselected,
            height: height,
            fadeInOpacity: new Animated.Value(0),
            selectedIndex: null
        };
    }
    componentDidMount() {
    }
    createAnimation = (index, height) => {
        return Animated.timing(
            this.state.height[index],
            {
                toValue: height,
                duration: 250
            }
        );
    }
    createFade = (value) => {
        return Animated.timing(
            this.state.fadeInOpacity,
            {
                toValue: value,
                duration: 250,
            }
        );
    }
    onSelect = (index) => {
        if (index === this.state.selectedIndex) {
            //消失
            this.hide(index);
        } else {
            this.setState({selectedIndex: index, current: index});
            this.onShow(index);
        }
    }
    hide = (index, subselected) => {
        let opts = {selectedIndex: null, current: index};
        if (subselected !== undefined) {
            this.state.subselected[index] = subselected;
            this.state.top[index] = this.props.config[index].data[subselected].title;
            opts = {selectedIndex: null, current: index, subselected: this.state.subselected.concat()};
        }
        this.setState(opts);
        this.onHide(index);
    }
    onShow = (index) => {
        Animated.parallel([this.createAnimation(index, this.state.maxHeight[index]), this.createFade(1)]).start();
    }
    onHide = (index) => {
        //其他的设置为0
        for (let i = 0, c = this.state.height.length; i < c; ++i) {
            if (index != i) {
                this.state.height[i].setValue(0);
            }
        }
        Animated.parallel([this.createAnimation(index, 0), this.createFade(0)]).start();
    }
    onSelectMenu = (index, subindex, data) => {
        this.hide(index, subindex);
        this.props.onSelectMenu && this.props.onSelectMenu(index, subindex, data);
    }
    renderList = (d, index) => {
        let subselected = this.state.subselected[index];
        let Comp = null;
        if (d.type == 'title') {
            Comp = Title;
        } else {
            Comp = Subtitle;
        }
        let enabled = this.state.selectedIndex == index || this.state.current == index;
        return (
            <Animated.View key={index} pointerEvents={enabled ? 'auto' : 'none'}
                           style={[styles.content, {opacity: enabled ? 1 : 0, height: this.state.height[index]}]}>
                <ScrollView style={styles.scroll}>
                    {d.data.map((data, subindex) => {
                        return <Comp
                            onSelectMenu={this.onSelectMenu}
                            index={index}
                            subindex={subindex}
                            data={data}
                            selected={subselected == subindex}
                            key={subindex}/>
                    })}
                </ScrollView>
            </Animated.View>
        );
    }
    render() {
        let list = null;
        if (this.state.selectedIndex !== null) {
            list = this.props.config[this.state.selectedIndex].data;
        }
        console.log(list);
        return (
            <View style={{flex: 1}}>
                <View style={styles.topMenu}>
                    {this.state.top.map((t, index) => {
                        return <TopMenuItem
                            key={index}
                            index={index}
                            onSelect={this.onSelect}
                            label={t}
                            selected={this.state.selectedIndex === index}/>
                    })}
                </View>
                {this.props.renderContent()}
                <View style={styles.bgContainer} pointerEvents={this.state.selectedIndex !== null ? "auto" : "none"}>
                    <Animated.View style={[styles.bg, {opacity: this.state.fadeInOpacity}]}/>
                    {this.props.config.map((d, index) => {
                        return this.renderList(d, index);
                    })}
                </View>
            </View>
        );
    }
}
const styles = StyleSheet.create({
    scroll: {flex: 1, backgroundColor: '#fff'},
    bgContainer: {position: 'absolute', top: 40, width: width, height: height},
    bg: {flex: 1, backgroundColor: 'rgba(50,50,50,0.2)'},
    content: {
        position: 'absolute',
        width: width
    },
    highlight: {
        color: COLOR_HIGH
    },
    marginHigh: {marginLeft: 10},
    margin: {marginLeft: 28},
    titleItem: {
        height: 43,
        alignItems: 'center',
        paddingLeft: 10,
        paddingRight: 10,
        borderBottomWidth: LINE,
        borderBottomColor: '#eee',
        flexDirection: 'row',
    },
    tableItem: {
        height: 43,
        alignItems: 'center',
        paddingLeft: 10,
        paddingRight: 10,
        borderBottomWidth: LINE,
        borderBottomColor: '#eee',
        flexDirection: 'row',
        justifyContent: 'space-between'
    },
    tableItemText: {fontWeight: '300', fontSize: 14},
    row: {
        flexDirection: 'row'
    },
    item: {
        flex: 1,
        flexDirection: 'row',
        alignItems: 'center',
        justifyContent: 'center',
    },
    menuTextHigh: {
        marginRight: 3,
        fontSize: 13,
        color: COLOR_HIGH
    },
    menuText: {
        marginRight: 3,
        fontSize: 13,
        color: COLOR_NORMAL
    },
    topMenu: {
        flexDirection: 'row',
        height: 40,
        borderTopWidth: LINE,
        borderTopColor: '#bdbdbd',
        borderBottomWidth: 1,
        borderBottomColor: '#f2f2f2'
    },
});

主类FoodView.js：

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */
import React, {Component} from 'react';
import {
    AppRegistry,
    StyleSheet,
    TouchableOpacity,
    Dimensions,
    Text,
    View
} from 'react-native';
const {width, height} = Dimensions.get('window');
import FoodActionBar from "./pop/FoodActionBar";
import Separator from "./util/Separator";
import TopMenu from "./pop/TopMenu";
const CONFIG = [
    {
        type:'subtitle',
        selectedIndex:1,
        data:[
            {title:'全部', subtitle:'1200m'},
            {title:'自助餐', subtitle:'300m'},
            {title:'自助餐', subtitle:'200m'},
            {title:'自助餐', subtitle:'500m'},
            {title:'自助餐', subtitle:'800m'},
            {title:'自助餐', subtitle:'700m'},
            {title:'自助餐', subtitle:'900m'},
        ]
    },
    {
        type:'title',
        selectedIndex:0,
        data:[{
            title:'智能排序'
        }, {
            title:'离我最近'
        }, {
            title:'好评优先'
        }, {
            title:'人气最高'
        }]
    }
];
export default class FoodView extends Component {
    constructor(props){
        super(props);
        this.state = {
            data:{}
        };
    }
    renderContent=()=>{
        return (
            <TouchableOpacity >
                <Text style={styles.text}>index:{this.state.index} subindex:{this.state.subindex} title:{this.state.data.title}</Text>
            </TouchableOpacity>
        );
        // alert(this.state.data.title)
    };
    onSelectMenu=(index, subindex, data)=>{
        this.setState({index, subindex, data});
    };
    render() {
        return (
            <View style={styles.container}>
                <FoodActionBar/>
                <Separator/>
                <TopMenu style={styles.container} config={CONFIG} onSelectMenu={this.onSelectMenu} renderContent={this.renderContent}/>
            </View>
        );
    }
}
const styles = StyleSheet.create({
    container: {
        flex: 1,
        width:width,
        backgroundColor: '#F5FCFF',
    },
    text: {
        fontSize:20,
        marginTop:100,
        justifyContent: 'center',
        alignItems: 'center',
    },
});