javascript - 如何使用 ES6 和 React Native

Question

使用 React-Native 并尝试学习 ES6 语法。我昨天遇到了类似的问题并得到了解决方案。我加了

.bind(this)

到我的函数调用，问题就解决了。我在另一个函数调用中再次遇到了同样的问题，但我无法追踪到底发生了什么。错误信息是一样的。

undefined is not a object (evaluating 'this.props.drawer.open')

函数是:

    onClickMenu () {
    this.props.drawer.open();
  }

它被这样调用:

onPress={this.onClickMenu.bind(this)}

这是完整的代码。如果您看到除此问题以外的其他问题，请告诉我! *注意我已经用“let”替换了“var”。根据我的阅读，正确的 ES6 语法在任何地方都可以做到这一点？

    'use strict';

const React = require('react-native');
const {
  Text,
  View,
  Component,
  StyleSheet,
  SwitchAndroid
} = React;

import { Button } from 'react-native-material-design';
import Store from 'react-native-simple-store';
import Underscore from 'underscore';
import RNGMap from 'react-native-gmaps';
import Polyline from 'react-native-gmaps/Polyline';
import Icon from 'react-native-vector-icons/Ionicons';
import SettingsService from './../settings/settings.service';
//import subdivisions from './subdivisions.json';
import commonStyles from './../common/styles';

let accessToken = null;
let userId = null;
let routeId = null;
let subdivisionId = null;

SettingsService.init('Android');

class Map extends Component {
  constructor(props) {
    super(props)
    this.state = {
      odometer: 0,
      mapWidth: 300,
      mapHeight: 300,
      enabled: false,
      isMoving: false,
      currentLocation: undefined,
      locationManager: undefined,
      paceButtonIcon: 'Start Trip',
      navigateButtonIcon: 'navigate',
      paceButtonStyle: commonStyles.disabledButton,
      // mapbox
      center: {
        lat: 40.7223,
        lng: -73.9878
      },
      zoom: 10,
      markers: []
    }
  }

  componentDidMount() {
    Store.get('token').then((token) => {
      accessToken = token.access_token;
      userId = token.userId;
    });
    let me = this,
      gmap = this.refs.gmap;

    this.locationManager = this.props.locationManager;

    // location event
    this.locationManager.on("location", function(location) {
      console.log('- location: ', JSON.stringify(location));
      me.setCenter(location);
      gmap.addMarker(me._createMarker(location));

      me.setState({
        odometer: (location.odometer / 1000).toFixed(1)
      });

      // Add a point to our tracking polyline
      if (me.polyline) {
        me.polyline.addPoint(location.coords.latitude, location.coords.longitude);
      }
    });
    // http event
    this.locationManager.on("http", function(response) {});
    // geofence event
    this.locationManager.on("geofence", function(geofence) {});
    // error event
    this.locationManager.on("error", function(error) {
      console.log('- ERROR: ', JSON.stringify(error));
    });
    // motionchange event
    this.locationManager.on("motionchange", function(event) {
      me.updatePaceButtonStyle();
    });

    // getGeofences
    this.locationManager.getGeofences(function(rs) {
    }, function(error) {
      console.log("- getGeofences ERROR", error);
    });

    SettingsService.getValues(function(values) {
      values.license = "eddbe81bbd86fa030ea466198e778ac78229454c31100295dae4bfc5c4d0f7e2";
      values.orderId = 1;
      values.stopTimeout = 0;
      //values.url = 'http://192.168.11.120:8080/locations';

      me.locationManager.configure(values, function(state) {
        me.setState({
          enabled: state.enabled
        });
        if (state.enabled) {
          me.initializePolyline();
          me.updatePaceButtonStyle()
        }
      });
    });

    this.setState({
      enabled: false,
      isMoving: false
    });
  }
  _createMarker(location) {
    return {
      title: location.timestamp,
      id: location.uuid,
      icon: require("image!transparent_circle"),
      anchor: [0.5, 0.5],
      coordinates: {
        lat: location.coords.latitude,
        lng: location.coords.longitude
      }
    };
  }

  initializePolyline() {
    // Create our tracking Polyline
    let me = this;
    Polyline.create({
      width: 12,
      points: [],
      geodesic: true,
      color: '#2677FF'
    }, function(polyline) {
      me.polyline = polyline;
    });
  }

  onClickMenu () {
    this.props.drawer.open();
  }

  onClickEnable() {
    let me = this;
    if (!this.state.enabled) {
      this.locationManager.start(function() {
        me.initializePolyline();
      });
    } else {
      this.locationManager.resetOdometer();
      this.locationManager.stop();
      this.setState({
        markers: [{}],
        odometer: 0
      });
      this.setState({
        markers: []
      });
      if (this.polyline) {
        this.polyline.remove(function(result) {
          me.polyline = undefined;
        });
      }
    }

    this.setState({
      enabled: !this.state.enabled
    });
    this.updatePaceButtonStyle();
  }

  onClickPace() {
    if (!this.state.enabled) {
      return;
    }
    let isMoving = !this.state.isMoving;
    this.locationManager.changePace(isMoving);

    this.setState({
      isMoving: isMoving
    });
    this.updatePaceButtonStyle();
  }

  onClickLocate() {
    let me = this;

    this.locationManager.getCurrentPosition({
      timeout: 30
    }, function(location) {
      me.setCenter(location);
    }, function(error) {
      console.error('ERROR: getCurrentPosition', error);
      me.setState({
        navigateButtonIcon: 'navigate'
      });
    });
  }

  onRegionChange() {}

  setCenter(location) {
    this.setState({
      navigateButtonIcon: 'navigate',
      center: {
        lat: location.coords.latitude,
        lng: location.coords.longitude
      },
      zoom: 16
    });
  }

  onLayout() {
    let me = this,
      gmap = this.refs.gmap;

    this.refs.workspace.measure(function(ox, oy, width, height, px, py) {
      me.setState({
        mapHeight: height,
        mapWidth: width
      });
    });
  }

  updatePaceButtonStyle() {
    let style = commonStyles.disabledButton;
    if (this.state.enabled) {
      style = (this.state.isMoving) ? commonStyles.redButton : commonStyles.greenButton;
    }
    this.setState({
      paceButtonStyle: style,
      paceButtonIcon: (this.state.enabled && this.state.isMoving) ? 'Stop Trip' : 'Start Trip'
    });
  }

  render() {
    return (
      <View style={commonStyles.container}>
        <View style={commonStyles.topToolbar}>
          <Icon.Button name="android-options" onPress={this.onClickMenu.bind(this)} backgroundColor="transparent" size={30} color="#000" style={styles.btnMenu} underlayColor={"transparent"} />
          <Text style={commonStyles.toolbarTitle}>Background Geolocation</Text>
          <SwitchAndroid onValueChange={this.onClickEnable.bind(this)} value={this.state.enabled} />
        </View>
        <View ref="workspace" style={styles.workspace} onLayout={this.onLayout.bind(this)}>

          <RNGMap
            ref={'gmap'}
            style={{width: this.state.mapWidth, height: this.state.mapHeight}}
            markers={this.state.markers}
            zoomLevel={this.state.zoom}
            onMapChange={(e) => console.log(e)}
            onMapError={(e) => console.log('Map error --> ', e)}
            center={this.state.center} />

        </View>
        <View style={commonStyles.bottomToolbar}>
          <Icon.Button name={this.state.navigateButtonIcon} onPress={this.onClickLocate.bind(this)} size={25} color="#000" underlayColor="#ccc" backgroundColor="transparent" style={styles.btnNavigate} />
          <Text style={{fontWeight: 'bold', fontSize: 18, flex: 1, textAlign: 'center'}}>{this.state.odometer} km</Text>
          <Button raised={true} 
                  text={this.state.paceButtonIcon} 
                  onPress={this.onClickPace.bind(this)}
                  overrides={{backgroundColor:"#e12429",textColor:"#ffffff"}} 
                  style={this.state.paceButtonStyle}></Button>
          <Text>&nbsp;</Text>
        </View>
      </View>
    );
  }
};

const styles = StyleSheet.create({
  workspace: {
    flex: 1
  }
});

module.exports = Map;

更新:在终端中通过 adb 调试显示相同的错误

所以这里是剩下的代码。进行故障排除。我将项目文件添加到 plunker。这是我正在使用的演示项目。 plunker

    'use strict';

const React = require('react-native');
const {
  Text, 
  Component,
  StyleSheet, 
  AppRegistry
} = React;

import Map from './map/map';
import Drawer from 'react-native-drawer';
import Settings from './settings/settings.android';
import Icon from 'react-native-vector-icons/Ionicons';
import BackgroundGeolocation from 'react-native-background-geolocation-android';

global.bgGeo = BackgroundGeolocation;

class App extends Component {
  onClickMenu() {
    this.props.refs.drawer.open();
  }

  render() {
    return (
      <Drawer ref="drawer" side="right" acceptPan={false} content={<Settings drawer={this.refs.drawer} locationManager={BackgroundGeolocation} />}>
        <Map drawer={this.refs.drawer} locationManager={BackgroundGeolocation} />    
      </Drawer>
    );
  }
};

module.exports = App;

更新:

Answer 1

我认为您不能以这种方式将引用传递给组件，当然它不会在 React 中工作，我认为它不会工作在 React-Native 中以这种方式。

我不清楚您为什么要尝试从 .open DrawerMap 组件，因为它看起来像 Map 组件只能是当 Drawer 打开时访问，但是，如果你想访问父级 child 的行为一个好的模式是通过函数让 child 执行(你可以争辩说这实际上很糟糕传递事件是一种更强大的模式)。

我从来没有使用过这个库，所以我不太清楚它的用法，但是你可以像这样传递函数:

class Application extends Component {

  closeControlPanel = () => {
    this.refs.drawer.close()
  };
  openControlPanel = () => {
    this.refs.drawer.open()
  };
  render () {
    return (
      <Drawer
        ref="drawer"
        content={<ControlPanel />}
        >
        <Map onMenuClose={ this.closeControlPanel.bind( this ) } />
      </Drawer>
    )
  }
})

在这种情况下，this.props.onMenuClose 应该附加到一个 Action ，当执行该 Action 时，将触发来自父级的函数并执行 this.refs.drawer.close 函数。