您试图在一个本应是不可变且已被冻结的对象上设置密钥

Question

在以下示例中：

• MapView 将ListView 的元素显示为注解
• 单击 ListView 元素应将其绘制成蓝色颜色。
• 如果MapView 和ListView 有效地使用状态对象，则会得到奖励

修改ListView的DataSource似乎会在active属性被修改时引起冲突：

您试图将键 'active' 设置为 本来应该是不可变的并且已被冻结的对象。

设置状态的正确方法是什么？

RNPlay Example

'use strict';

import React, {Component} from 'react';
import {AppRegistry,View,ListView,MapView,Text,TouchableOpacity} from 'react-native';

var annotations = [
        {
          title: 'A',active: false,latitude: 45,longitude: 26,latitudeDelta: 0.015,longitudeDelta: 0.015,
        },{
          title: 'B',active: false,latitude: 49,longitude: 14,latitudeDelta: 0.015,longitudeDelta: 0.015,
        },{
          title: 'C',active: false,latitude: 26,longitude: 25,latitudeDelta: 0.015,longitudeDelta: 0.015,
        }
      ]

class SampleApp extends Component {

  constructor(props) {
    super(props);
    var ds = new ListView.DataSource({
        rowHasChanged: (row1, row2) => row1 !== row2,
    });
    this.state = {
      region: annotations[0],
      annotations: annotations,
      dataSource: ds.cloneWithRows(annotations)
    };
  }

  handleClick(field) {
    if (this.previousField) {
      this.previousField.active = false;
    }
    this.previousField = field;
    field.active = true;
    this.setState({
      region: field,
    });
  }

  renderField(field) {
    let color = (field.active == true)?'blue':'yellow'; 

    return (
      <TouchableOpacity onPress={this.handleClick.bind(this,field)}>
        <Text style={{backgroundColor:color,borderWidth:1}}>{field.title}</Text>
      </TouchableOpacity>
    );
  }

  render() {
    return (
      <View style={{flex:1,flexDirection:'column',alignSelf:'stretch'}}>
        <MapView
            style={{flex:0.5,alignSelf:'stretch',borderWidth:1}}
          region={this.state.region}
          annotations={this.state.annotations}
        />
        <ListView
          dataSource={this.state.dataSource}
          renderRow={(field) => this.renderField(field)}
        />
      </View>
    );
  }
}

AppRegistry.registerComponent('SampleApp', () => SampleApp);

Answer 1

问题

当您设置field.active = true; 或this.previousField.active = false; 时，您正在修改ListView 的数据源中存在的对象(field)。 ListView 会引发错误，因为当您使用 cloneWithRows 创建它时，它会冻结其数据源。这是为了确保不能在正常的 React 组件生命周期之外修改数据源（如 setState）。相反，ListView.DataSource 对象被设计为使用cloneWithRows 进行更改，这将返回现有数据源的副本。

如果您熟悉 Redux 库，它与让 reducer 函数返回状态的副本而不是修改现有状态的理念非常相似。

克隆数据源

为了解决这个问题，你真正想要做的是创建一个已经设置值的新数据数组（如active），然后调用@987654334 @ 为您的 ListView 使用 cloneWithRows 创建的新数据源。如果你这样做，你实际上甚至根本不需要你所在州的annotations 键。

这里的代码可能比文字更有帮助：

handleClick(field) {

  //iterate over annotations, and update them.
  //I'm taking 'title' as a unique id property for each annotation, 
  //for the sake of the example.
  const newAnnotations = annotations.map(a => {
    //make a copy of the annotation.  Otherwise you'll be modifying
    //an object that's in your listView's datasource,
    //and therefore frozen.
    let copyA = {...a};
    if (copyA.title === field.title) {
      copyA.active = true;
    } else {
      copyA.active = false;
    }
    return copyA;
  });

  this.setState({
    region: {...field, active: true},
    dataSource: this.state.dataSource.cloneWithRows(newAnnotations),
  });
}

我希望这会有所帮助！这是一个包含您发布的完整代码的代码 sn-p 以及我的修改。正如您在使用 React Native 0.29 的 iOS 上描述的那样，它对我有用。您标记了问题 android-mapview，所以我假设您运行的是 Android，但在这种情况下，平台应该不会真正产生影响。

'use strict';

import React, {Component} from 'react';
import {AppRegistry,View,ListView,MapView,Text,TouchableOpacity} from 'react-native';

var annotations = [
        {
          title: 'A',active: false,latitude: 45,longitude: 26,latitudeDelta: 0.015,longitudeDelta: 0.015,
        },{
          title: 'B',active: false,latitude: 49,longitude: 14,latitudeDelta: 0.015,longitudeDelta: 0.015,
        },{
          title: 'C',active: false,latitude: 26,longitude: 25,latitudeDelta: 0.015,longitudeDelta: 0.015,
        }
      ]

class SampleApp extends Component {

  constructor(props) {
    super(props);
    var ds = new ListView.DataSource({
        rowHasChanged: (row1, row2) => row1 !== row2,
    });
    this.state = {
      region: annotations[0],
      dataSource: ds.cloneWithRows(annotations)
    };
  }

  handleClick(field) {

    //iterate over annotations, and update them.
    //I'm taking 'title' as a unique id property for each annotation, 
    //for the sake of the example.
    const newAnnotations = annotations.map(a => {
      //make a copy of the annotation.  Otherwise you'll be modifying
      //an object that's in your listView's datasource,
      //and therefore frozen.
      let copyA = {...a};
      if (copyA.title === field.title) {
        copyA.active = true;
      } else {
        copyA.active = false;
      }
      return copyA;
    });

    this.setState({
      region: {...field, active: true},
      dataSource: this.state.dataSource.cloneWithRows(newAnnotations),
    });
  }

  renderField(field) {
    console.log(field);
    let color = (field.active == true)?'blue':'yellow';

    return (
      <TouchableOpacity onPress={this.handleClick.bind(this,field)}>
        <Text style={{backgroundColor:color,borderWidth:1}}>{field.title}</Text>
      </TouchableOpacity>
    );
  }

  render() {
    return (
      <View style={{flex:1,flexDirection:'column',alignSelf:'stretch'}}>
        <MapView
          style={{flex:0.5,alignSelf:'stretch',borderWidth:1}}
          region={this.state.region}
          annotations={this.state.annotations}
        />
        <ListView
          dataSource={this.state.dataSource}
          renderRow={(field) => this.renderField(field)}
        />
      </View>
    );
  }
}

AppRegistry.registerComponent('SampleApp', () => SampleApp);