Picker选择器，可以自由创建Item用来选择
主要属性：

selectedValue：选择的值，可以是value属性值
onValueChange：方法，提供两个参数，一个是被选中项的value属性，一个是索引位置
<Picker.Item/>：为picker的item

创建一个picker：

<Picker style={{width: 300, height: 200, backgroundColor: "#ffaaff"}}
                    selectedValue={this.state.language}
                    onValueChange={(lang)=>this.setState({language: lang})}>
                <Picker.Item label="Java" value="java" />
                <Picker.Item label="JavaScript" value="js" />
                <Picker.Item label="Swift" value="swift" />
                <Picker.Item label="Object-c" value="oc" />
                <Picker.Item label="Php" value="php" />
                <Picker.Item label="Html" value="html" />
                <Picker.Item label="Css" value="css" />
                <Picker.Item label="C++" value="c++" />
            </Picker>

PickerIOS针对于iOS版本的picker
主要属性没变
创建一个PickerIOS：

CAR_MAKES_AND_MODELS参数可以在完整代码中查看
<PickerIOS style={{width: 300, height: 200, backgroundColor: '#11fff1'}}
                       selectedValue={this.state.carMake}
                       onValueChange={(itemValue)=>this._iosValue11(itemValue)}
                >
                    {
                        Object.keys(CAR_MAKES_AND_MODELS).map((carmake)=>(
                             <Picker.ItemIOS
                                 key={carmake}
                                 value={carmake}
                                 label={CAR_MAKES_AND_MODELS[carmake].name}
                             />
                    ))
                    }
                </PickerIOS>

完整代码：

import React, { Component } from 'react';
import {
    AppRegistry,
    Picker,
    PickerIOS,
    View
} from 'react-native';
var CAR_MAKES_AND_MODELS = {
    amc: {
        name: 'AMC',
        models: ['AMX', 'Concord', 'Eagle', 'Gremlin', 'Matador', 'Pacer'],
    },
    alfa: {
        name: 'Alfa-Romeo',
        models: ['159', '4C', 'Alfasud', 'Brera', 'GTV6', 'Giulia', 'MiTo', 'Spider'],
    },
    aston: {
        name: 'Aston Martin',
        models: ['DB5', 'DB9', 'DBS', 'Rapide', 'Vanquish', 'Vantage'],
    },
};
export default class RNPickerView extends Component {
    constructor(props){
        super(props);
        this.state = {
            language: 'java',
            selectCount: 0,
            carMake: 'amc',
        }
    }
    _pickerView = ()=>{
        return(
            <Picker style={{width: 300, height: 200, backgroundColor: "#ffaaff"}}
                    selectedValue={this.state.language}
                    onValueChange={(lang)=>this.setState({language: lang})}>
                <Picker.Item label="Java" value="java" />
                <Picker.Item label="JavaScript" value="js" />
                <Picker.Item label="Swift" value="swift" />
                <Picker.Item label="Object-c" value="oc" />
                <Picker.Item label="Php" value="php" />
                <Picker.Item label="Html" value="html" />
                <Picker.Item label="Css" value="css" />
                <Picker.Item label="C++" value="c++" />
            </Picker>
        )
    };
    _iosValue11 = (item)=> {
        console.log('_iosValue11' + item);
        this.setState({
            carMake: item
        })
    };
    _iosValue22 = (item)=> {
        console.log('_iosValue22' + item);
        this.setState({
            selectCount: item
        })
    };
    _pickerIOS = ()=>{
        let make = CAR_MAKES_AND_MODELS[this.state.carMake];
        let selectIndex = make.name + ' ' + make.models[this.state.selectCount];
        return(
            <View>
                <PickerIOS style={{width: 300, height: 200, backgroundColor: '#11fff1'}}
//这里的selectedValue选择的是value
                       selectedValue={this.state.carMake}
//onValueChange中的传递参数是value属性，保证和selectedValue的属性一样
                       onValueChange={(itemValue)=>this._iosValue11(itemValue)}
                >
                    {
//这里是有map函数变量了CAR_MAKES_AND_MODELS对象中的keys值
                        Object.keys(CAR_MAKES_AND_MODELS).map((carmake)=>(
                             <Picker.ItemIOS
                                 key={carmake}
                                 value={carmake}
                                 label={CAR_MAKES_AND_MODELS[carmake].name}
                             />
                    ))
                    }
                </PickerIOS>
                <PickerIOS style={{width: 300, height: 200, backgroundColor: '#11fff1'}}
//selectedValue 选择的是索引位置
                selectedValue={this.state.selectCount}
//onValueChange中的传递参数是value属性，保证和selectedValue的属性一样，这里的value是索引位置
                onValueChange={(itemValue)=>this._iosValue22(itemValue)}>
                    {
//这里map遍历的是models数组，modelName为数组的value，modelIndex数组位置

CAR_MAKES_AND_MODELS[this.state.carMake].models.map((modelName, modelIndex)=>(
                            <Picker.ItemIOS
                                key={this.state.carMake + '_' + modelIndex}
                                value={modelIndex}
                                label={modelName}
                            />
                        ))
                    }
                </PickerIOS>
            </View>
        )
    };
    render() {
        return(
            <View style={{flex: 1, backgroundColor: "#aaffaa", alignItems: 'center', justifyContent: 'center'}}>
                {this._pickerView()}
                {this._pickerIOS()}
            </View>
        )
    }
}
AppRegistry.registerComponent('RNPickerView', ()=> RNPickerView);

效果图：

CA479814-0E51-47D5-8FC7-C99A714EF90F.png