[英]React Native and Refs - Why does this function not return my content?
我在React Native中有以下代碼:
'use strict'
import React, { Component } from 'react';
import { AppRegistry, Animated, Dimensions, Easing, Image, Text, View, StyleSheet, TouchableOpacity, ScrollView } from 'react-native';
const categoryTwoLinks = [
{ label: 'Subcategory1' },
{ label: 'Subcategory2' },
{ label: 'Subcategory3' },
{ label: 'Subcategory4' },
{ label: 'Subcategory5' },
{ label: 'Subcategory6' },
]
const categoryTouts = [
{ image: require('./assets/images/image01.jpg'), title: 'Category1' },
{ image: require('./assets/images/image02.jpg'), title: 'Category2', links: categoryTwoLinks },
{ image: require('./assets/images/image03.jpg'), title: 'Category3' },
]
class Tout extends Component {
render() {
console.log('tout')
return (
<Image
source={this.props.image}
ratioGrow
alignItems='center'
style={{ alignItems: 'center', justifyContent: 'center' }}
>
<Text
style={{ color: 'white', fontSize: 24, backgroundColor: 'transparent', fontWeight: 'bold' }}
>
{this.props.title}
</Text>
</Image>
)
}
}
export default class scrollAccordion extends Component {
handleScroll = ({ nativeEvent: { contentOffset } }: Object) => {
const scrollY = contentOffset.y
this.scrollOffsetValue.setValue(scrollY)
}
setScrollRef = node => {
console.log('set scroll ref')
if (node) {
this.scrollRef = node
}
}
renderCategoryTouts = () => {
console.log('render category tout')
categoryTouts.map((tout, index) => {
return (
<Tout
key={tout.title}
{...tout}
scrollViewRef={this.state.scrollRef}
scrollOffset={this.scrollOffsetValue}
/>
)
})
}
render() {
console.log('render')
let categoryTouts = this.scrollRef ? this.renderCategoryTouts() : null
return (
<View style={styles.container}>
<ScrollView
scrollEventThrottle={1}
ref={this.setScrollRef}
onScroll={this.handleScroll}
>
<View>
{categoryTouts}
</View>
</ScrollView>
</View>
)
}
}
const styles = StyleSheet.create({
container: {
flex: 1,
alignItems: 'center',
justifyContent: 'center',
paddingTop: 40,
backgroundColor: 'white',
},
toutText: {
color: 'white', backgroundColor: 'transparent', fontWeight: 'bold', fontSize: 24
}
});
AppRegistry.registerComponent('scrollAccordion', () => scrollAccordion);
不會從renderCategoryTouts
函數返回任何內容。
我知道,最初, this.scrollRef
是未定義的,因此主渲染函數將為{categoryTouts}
變量返回{null}
。 但是在設置scrollRef之后,我需要它返回renderCategoryTouts
的結果。 我該如何工作?
在您的renderCategoryTouts函數中,您具有變量categoryTouts變量。 您從未在此函數中聲明過像這樣的變量,因此我認為它是全局變量。
renderCategoryTouts = () => {
categoryTouts.map((tout, index) => {
return (
<Tout
key={tout.title}
{...tout}
scrollViewRef={this.state.scrollRef}
scrollOffset={this.scrollOffsetValue}
/>
)
})
}
在此函數中,您使用this.state.scrollRef,this.scrollOffsetValue,因此您需要綁定此函數。(建議您在類的構造函數中進行此操作)
this.renderCategoryTouts = this.renderCategoryTouts.bind(this)
另外,如果這不能正常工作,那么完整的代碼將非常有幫助
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