在React-Native FlatList中突出显示所选项

Question

我整理了一个简单的React-native应用程序来从远程服务获取数据,将其加载到FlatList中.当用户点击某个项目时,应突出显示该项目并保留选择.我相信这样一个微不足道的行动应该不难.我不确定我错过了什么.

import React, { Component } from 'react';
import {
  StyleSheet,
  Text,
  View,
  FlatList,
  ActivityIndicator,
  Image,
  TouchableOpacity,
} from 'react-native';

export default class BasicFlatList extends Component {
  constructor(props) {
    super(props);

    this.state = {
      loading: false,
      data: [],
      page: 1,
      seed: 1,
      error: null,
      refreshing: false,
      selectedItem:'null',
    };
  }

  componentDidMount() {
    this.makeRemoteRequest();
  }

  makeRemoteRequest = () => {
    const {page, seed} = this.state;
    const url = `https://randomuser.me/api/?seed=${seed}&page=${page}&results=20`;
    this.setState({loading: true});
    fetch(url)
      .then(res => res.json())
      .then(res => {
        this.setState({
          data: page === 1 ? res.results : [...this.state.data, ...res.results],
          error: res.error || null,
          loading: false,
          refreshing: false
        });
      })
      .catch(error => {
        this.setState({error, loading: false});
      });
  };

  onPressAction = (rowItem) => {
    console.log('ListItem was selected');
    console.dir(rowItem);
    this.setState({
      selectedItem: rowItem.id.value
    });
  }

  renderRow = (item) => {
    const isSelectedUser = this.state.selectedItem === item.id.value;
    console.log(`Rendered item - ${item.id.value} for ${isSelectedUser}`);
    const viewStyle = isSelectedUser ? styles.selectedButton : styles.normalButton;
    return(
        <TouchableOpacity style={viewStyle} onPress={() => this.onPressAction(item)} underlayColor='#dddddd'>
          <View style={styles.listItemContainer}>
            <View>
              <Image source={{ uri: item.picture.large}} style={styles.photo} />
            </View>
            <View style={{flexDirection: 'column'}}>
              <View style={{flexDirection: 'row', alignItems: 'flex-start',}}>
                {isSelectedUser ?
                  <Text style={styles.selectedText}>{item.name.first} {item.name.last}</Text>
                  : <Text style={styles.text}>{item.name.first} {item.name.last}</Text>
                }
              </View>
              <View style={{flexDirection: 'row', alignItems: 'flex-start',}}>
                <Text style={styles.text}>{item.email}</Text>
              </View>
            </View>
          </View>
        </TouchableOpacity>
    );
  }

  render() {
    return(
      <FlatList style={styles.container}
        data={this.state.data}
        renderItem={({ item }) => (
          this.renderRow(item)
        )}
      />
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    marginTop: 50,
  },
  selectedButton: {
    backgroundColor: 'lightgray',
  },
  normalButton: {
    backgroundColor: 'white',
  },
  listItemContainer: {
    flex: 1,
    padding: 12,
    flexDirection: 'row',
    alignItems: 'flex-start',
  },
  text: {
    marginLeft: 12,
    fontSize: 16,
  },
  selectedText: {
    marginLeft: 12,
    fontSize: 20,
  },
  photo: {
    height: 40,
    width: 40,
    borderRadius: 20,
  },
});

当用户点击列表中的项目时,将使用所选项目的信息调用"onPress"方法.但是Flatlist中突出显示项目的下一步不会发生.'UnderlayColor'也没有任何帮助.

任何帮助/建议将不胜感激.

Answer 1

您可以执行以下操作：

1. 对于renderItem，使用TouchableOpacity 之类的东西，通过onPress 事件传递renderItem 的索引或id；

2. 将所选项目添加到状态的函数：

   handleSelection = (id) => {
      var selectedId = this.state.selectedId
   
      if(selectedId === id)
        this.setState({selectedItem: null})
      else 
        this.setState({selectedItem: id})
   }
   
   handleSelectionMultiple = (id) => {
      var selectedIds = [...this.state.selectedIds] // clone state
   
      if(selectedIds.includes(id))
        selectedIds = selectedIds.filter(_id => _id !== id)
      else 
        selectedIds.push(id)
   
      this.setState({selectedIds})
   }
   

3. 平面列表：

   <FlatList
     data={data}
     extraData={
       this.state.selectedId     // for single item
       this.state.selectedIds    // for multiple items
     }
     renderItem={(item) => 
        <TouchableOpacity 
   
          // for single item
          onPress={() => this.handleSelection(item.id)}
          style={item.id === this.state.selectedId ? styles.selected : null} 
   
          // for multiple items
          onPress={() => this.handleSelectionMultiple(item.id)}
          style={this.state.selectedIds.includes(item.id) ? styles.selected : null} 
        >
           <Text>{item.name}</Text>
        </TouchableOpacity>
     }
   

   />

4. 为所选项目创建一个样式，就是这样！

Answer 2

您应该将extraData道具传递到FlatList，以便它将根据您的选择重新渲染项目

这里 ：

<FlatList style={styles.container}
    data={this.state.data}
    extraData={this.state.selectedItem}
    renderItem={({ item }) => (
      this.renderRow(item)
    )}
 />

来源：https : //facebook.github.io/react-native/docs/flatlist

确保您的renderItem函数所依赖的所有内容都作为更新后不是===的道具（例如extraData）传递，否则您的UI可能不会根据更改进行更新

Answer 3

代替this.state.selectedItem和设置/检查a rowItem.id.value,我建议使用具有键:值对的Map对象,如RN FlatList文档示例中所示:https://facebook.github.io/react-native/docs/flatlist . HTML.另请参阅js Map文档:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map.

@ jI-V推荐的extraData prop将确保当this.state.selected在选择时发生更改时会重新呈现.

您的onPressAction显然会从下面的示例中改变一点,具体取决于您是否要在任何给定时间限制选择的数量,或者不允许用户切换选择等.

另外,虽然没有必要通过任何方式,但我喜欢使用另一个类或纯组件作为renderItem组件; 最终看起来像下面这样:

export default class BasicFlatList extends Component {
  state = {
    otherStateStuff: ...,
    selected: (new Map(): Map<string, boolean>) //iterable object with string:boolean key:value pairs
  }

  onPressAction = (key: string) => {
    this.setState((state) => {
      //create new Map object, maintaining state immutability
      const selected = new Map(state.selected);
      //remove key if selected, add key if not selected
      this.state.selected.has(key) ? selected.delete(key, !selected.get(key)) : selected.set(key, !selected.get(key));
      return {selected};
    });
  }

  renderRow = (item) => {
    return (
        <RowItem
          {...otherProps}
          item={item}
          onPressItem={this.onPressAction}
          selected={!!this.state.selected.get(item.key)} />
    );
  }

  render() {
    return(
      <FlatList style={styles.container}
        data={this.state.data}
        renderItem={({ item }) => (
          this.renderRow(item)
        )}
        extraData={this.state}
      />
    );
  }
}


class RowItem extends Component {
  render(){
    //render styles and components conditionally using this.props.selected ? _ : _
    
    return (
      <TouchableOpacity onPress={this.props.onPressItem}>
        ...
      </TouchableOpacity>
    )
  }
}