Question

我遇到此错误。

不变违规：元素类型无效：预期为字符串（对于内置组件）或类/函数（对于复合组件），但得到：未定义。您可能忘记了从定义文件中导出组件，或者可能混淆了默认导入和命名导入。

检查ListScreen的呈现方法。

想知道是什么问题。多谢您的协助。谢谢

ListScreen.js

import React, { Component } from 'react'
import { Alert, Dimensions, Platform, View } from 'react-native'
import { Button, Header, Icon, Input, Item, Left, Right, Text } from 'native-base'
import UltimateListView from 'react-native-ultimate-listview'
// import { UltimateListView } from '../lib/index'
import styles from './Styles/ListScreenStyles'
import LoadingSpinner from '../Components/LoadingSpinner'
import ControlTab from '../Components/ControlTab'
import FlatListItem from '../Components/FlatListItem'
import FlatListGrid from '../Components/FlatListGrid'

const { width, height } = Dimensions.get('window')
export default class ListScreen extends Component {
  constructor(props) {
    super(props)
    this.state = {
      layout: 'list',
      text: ''
    }
  }

  onFetch = async (page = 1, startFetch, abortFetch) => {
    try {
      // This is required to determinate whether the first loading list is all loaded.
      let pageLimit = 24
      if (this.state.layout === 'grid') pageLimit = 60
      const skip = (page - 1) * pageLimit

      // Generate dummy data
      let rowData = Array.from({ length: pageLimit }, (value, index) => `item -> ${index + skip}`)

      // Simulate the end of the list if there is no more data returned from the server
      if (page === 10) {
        rowData = []
      }

      // Simulate the network loading in ES7 syntax (async/await)
      await this.sleep(2000)
      startFetch(rowData, pageLimit)
    } catch (err) {
      abortFetch() // manually stop the refresh or pagination if it encounters network error
      console.log(err)
    }
  }

  onChangeLayout = (event) => {
    this.setState({ text: '' })
    switch (event.nativeEvent.selectedSegmentIndex) {
      case 0:
        this.setState({ layout: 'list' })
        break
      case 1:
        this.setState({ layout: 'grid' })
        break
      default:
        break
    }
  }

  onChangeScrollToIndex = (num) => {
    this.setState({ text: num })
    let index = num
    if (this.state.layout === 'grid') {
      index = num / 3
    }
    try {
      this.listView.scrollToIndex({ viewPosition: 0, index: Math.floor(index) })
    } catch (err) {
      console.warn(err)
    }
  }

  onPressItem = (type, index, item) => {
    Alert.alert(type, `You're pressing on ${item}`)
  }

  sleep = time => new Promise(resolve => setTimeout(() => resolve(), time))

  renderItem = (item, index, separator) => {
    if (this.state.layout === 'list') {
      return (
        <FlatListItem item={item} index={index} onPress={this.onPressItem} />
      )
    } else if (this.state.layout === 'grid') {
      return (
        <FlatListGrid item={item} index={index} onPress={this.onPressItem} />
      )
    }
    return null
  }

  renderControlTab = () => (
    <ControlTab
      layout={this.state.layout}
      onChangeLayout={this.onChangeLayout}
    />
  )

  renderHeader = () => (
    <View>
      <View style={styles.header}>
        <Text style={{ textAlign: 'center' }}>I am the Header View, you can put some Instructions or Ads Banner here!
        </Text>
      </View>
      <View style={styles.headerSegment}>
        <Left style={{ flex: 0.15 }} />
        {this.renderControlTab()}
        <Right style={{ flex: 0.15 }} />
      </View>
    </View>
  )

  renderPaginationFetchingView = () => (
    <LoadingSpinner height={height * 0.2} text="loading..." />
  )

  render() {
    return (
      <View style={styles.container}>
        <Header searchBar rounded>
          <Item style={{ backgroundColor: 'lightgray', borderRadius: 5 }}>
            <Icon name="ios-search" />
            <Input placeholder="Search" onChangeText={this.onChangeScrollToIndex} value={this.state.text} />
          </Item>
        </Header>
        <UltimateListView
          ref={ref => this.listView = ref}
          key={this.state.layout} // this is important to distinguish different FlatList, default is numColumns
          onFetch={this.onFetch}
          keyExtractor={(item, index) => `${index} - ${item}`} // this is required when you are using FlatList
          refreshableMode="advanced" // basic or advanced

          item={this.renderItem} // this takes three params (item, index, separator)
          numColumns={this.state.layout === 'list' ? 1 : 3} // to use grid layout, simply set gridColumn > 1

          // ----Extra Config----
          displayDate
          header={this.renderHeader}
          paginationFetchingView={this.renderPaginationFetchingView}
          // sectionHeaderView={this.renderSectionHeaderView}   //not supported on FlatList
          // paginationFetchingView={this.renderPaginationFetchingView}
          // paginationAllLoadedView={this.renderPaginationAllLoadedView}
          // paginationWaitingView={this.renderPaginationWaitingView}
          // emptyView={this.renderEmptyView}
          // separator={this.renderSeparatorView}

          // new props on v3.2.0
          arrowImageStyle={{ width: 20, height: 20, resizeMode: 'contain' }}
          dateStyle={{ color: 'lightgray' }}
          refreshViewStyle={Platform.OS === 'ios' ? { height: 80, top: -80 } : { height: 80 }}
          refreshViewHeight={80}
        />
      </View>
    )
  }
}

Navigation.js

import { StackNavigator } from 'react-navigation'
import LaunchScreen from '../Containers/LaunchScreen'
import ListScreen from '../Containers/ListScreen'

import styles from './Styles/NavigationStyles'

// Manifest of possible screens
const PrimaryNav = StackNavigator({
  LaunchScreen: { screen: LaunchScreen },
  ListScreen: { screen: ListScreen }
}, {
  // Default config for all screens
  headerMode: 'none',
  initialRouteName: 'ListScreen',
  navigationOptions: {
    headerStyle: styles.header
  }
})

export default PrimaryNav

Answer 1

如react-native-ultimate-listview的{{3}}中所述，这是一个重大变化，您需要将react-native-ultimate-listview导入为

import { UltimateListView } from 'react-native-ultimate-listview'

响应本机不变变量：元素类型无效：预期为字符串（对于内置组件）或类/函数

1 个答案: