Error: Cannot read property 'State' of undefined
Error: Cannot read property 'State' of undefined
来自调试器和屏幕的错误
我从本地 api 创建了一个博客 post,目的是单击 "read more" 按钮导航到根据 id 检索其他剩余项目。但是,我使用了导航,但它给出了一个错误“无法读取未定义的 属性 'state'。
import React, {Component} from 'react';
import { StyleSheet, Text, View} from 'react-native';
import Post from './components/Post';
import PostSingle from './components/PostSingle';
import { createStackNavigator, createAppContainer } from 'react-navigation';
const RootStack = createStackNavigator(
{
PostScreen: { screen: Post},
PostSingleScreen:{screen: PostSingle},
}
);
const AppNavigator = createAppContainer(RootStack);
export default class App extends Component {
constructor(props) {
super(props);
};
render() {
return (
<View style={styles.container}>
<AppNavigator/>
</View>
);
}
}
Post.js
屏幕加载到 POST,从中按下阅读更多按钮以触发 PostSingle
import React, { Component } from 'react';
import {
ScrollView,
StyleSheet,
View,
Text,
InputText,
TouchableOpacity
} from 'react-native';
import axios from 'axios';
export default class Post extends Component{
constructor(props){
super(props);
this.state = {
posts: []
}
}
readMore = (id) => {
this.setState({ id: id})
this.props.navigation.navigate('PostSingleScreen')
}
componentDidMount(){
axios.get(`http://localhost/rest_api_myblog/api/post/read.php`)
//.then(json => console.log(json.data.data[0].id))
.then(json => json.data.data.map(mydata =>(
{
title: mydata.title,
body: mydata.body,
author: mydata.author,
category_name: mydata.category_name,
id: mydata.id
}
)))
//.then(newData => console.log(newData))
.then(newData => this.setState({posts: newData}))
.catch(error => alert(error))
}
render(){
return (
<View>
<ScrollView style={styles.scrollContent}>
<View style={styles.header}>
<Text style={styles.headerText}>Gist Monger</Text>
</View>
{
this.state.posts.map((post, index) =>(
<View key={index} style={styles.container}>
<Text style={styles.display}>
Author: {post.author}
</Text>
<Text style={styles.display}>
Category: {post.category_name}
</Text>
<Text style={styles.display}>
Title: {post.title}
</Text>
<Text style={{overflow:'hidden'}}>
Id: {post.id}
</Text>
<TouchableOpacity style={styles.buttonContainer}
onPress = {() => this.readMore(post.id)}
>
<Text style={styles.buttonText}>
Read More
</Text>
</TouchableOpacity>
</View>
))
}
</ScrollView>
<View style={styles.footer}></View>
</View>
);
}
}
PostSingle.js
PostSingle 预计将根据在 post 上单击的项目的 ID 显示单个 post。
import React, { Component } from 'react';
import {
ScrollView,
StyleSheet,
View,
Text,
TouchableOpacity
} from 'react-native';
import axios from 'axios';
export default class Post extends Component{
constructor(props){
super(props);
this.state = {
posts: []
}
}
componentDidMount(){
axios.get(`http://localhost/rest_api_myblog/api/post/read_single.php?id=${id}`)
.then(json => json.data.data.map(mydata =>(
{
title: mydata.title,
body: mydata.body,
author: mydata.author,
category_name: mydata.category_name,
body: mydata.body
}
)))
.then(newData => this.setState({posts: newData}))
.catch(error => alert(error))
}
render(){
return (
<View>
<ScrollView style={styles.scrollContent}>
<View style={styles.header}>
<Text style={styles.headerText}>Gist Monger</Text>
</View>
{
this.state.posts.map((post, index) =>(
<View key={index} style={styles.container}>
<Text style={styles.display}>
Author: {post.author}
</Text>
<Text style={styles.display}>
Category: {post.category_name}
</Text>
<Text style={styles.display}>
Title: {post.title}
</Text>
<Text style={{overflow:'hidden'}}>
Body: {post.body}
</Text>
</View>
))
}
</ScrollView>
<View style={styles.footer}></View>
</View>
);
}
}
您必须安装 react-native-gesture-handler
和 react-navigation
。参见 this
我从本地 api 创建了一个博客 post,目的是单击 "read more" 按钮导航到根据 id 检索其他剩余项目。但是,我使用了导航,但它给出了一个错误“无法读取未定义的 属性 'state'。
import React, {Component} from 'react';
import { StyleSheet, Text, View} from 'react-native';
import Post from './components/Post';
import PostSingle from './components/PostSingle';
import { createStackNavigator, createAppContainer } from 'react-navigation';
const RootStack = createStackNavigator(
{
PostScreen: { screen: Post},
PostSingleScreen:{screen: PostSingle},
}
);
const AppNavigator = createAppContainer(RootStack);
export default class App extends Component {
constructor(props) {
super(props);
};
render() {
return (
<View style={styles.container}>
<AppNavigator/>
</View>
);
}
}
Post.js 屏幕加载到 POST,从中按下阅读更多按钮以触发 PostSingle
import React, { Component } from 'react';
import {
ScrollView,
StyleSheet,
View,
Text,
InputText,
TouchableOpacity
} from 'react-native';
import axios from 'axios';
export default class Post extends Component{
constructor(props){
super(props);
this.state = {
posts: []
}
}
readMore = (id) => {
this.setState({ id: id})
this.props.navigation.navigate('PostSingleScreen')
}
componentDidMount(){
axios.get(`http://localhost/rest_api_myblog/api/post/read.php`)
//.then(json => console.log(json.data.data[0].id))
.then(json => json.data.data.map(mydata =>(
{
title: mydata.title,
body: mydata.body,
author: mydata.author,
category_name: mydata.category_name,
id: mydata.id
}
)))
//.then(newData => console.log(newData))
.then(newData => this.setState({posts: newData}))
.catch(error => alert(error))
}
render(){
return (
<View>
<ScrollView style={styles.scrollContent}>
<View style={styles.header}>
<Text style={styles.headerText}>Gist Monger</Text>
</View>
{
this.state.posts.map((post, index) =>(
<View key={index} style={styles.container}>
<Text style={styles.display}>
Author: {post.author}
</Text>
<Text style={styles.display}>
Category: {post.category_name}
</Text>
<Text style={styles.display}>
Title: {post.title}
</Text>
<Text style={{overflow:'hidden'}}>
Id: {post.id}
</Text>
<TouchableOpacity style={styles.buttonContainer}
onPress = {() => this.readMore(post.id)}
>
<Text style={styles.buttonText}>
Read More
</Text>
</TouchableOpacity>
</View>
))
}
</ScrollView>
<View style={styles.footer}></View>
</View>
);
}
}
PostSingle.js PostSingle 预计将根据在 post 上单击的项目的 ID 显示单个 post。
import React, { Component } from 'react';
import {
ScrollView,
StyleSheet,
View,
Text,
TouchableOpacity
} from 'react-native';
import axios from 'axios';
export default class Post extends Component{
constructor(props){
super(props);
this.state = {
posts: []
}
}
componentDidMount(){
axios.get(`http://localhost/rest_api_myblog/api/post/read_single.php?id=${id}`)
.then(json => json.data.data.map(mydata =>(
{
title: mydata.title,
body: mydata.body,
author: mydata.author,
category_name: mydata.category_name,
body: mydata.body
}
)))
.then(newData => this.setState({posts: newData}))
.catch(error => alert(error))
}
render(){
return (
<View>
<ScrollView style={styles.scrollContent}>
<View style={styles.header}>
<Text style={styles.headerText}>Gist Monger</Text>
</View>
{
this.state.posts.map((post, index) =>(
<View key={index} style={styles.container}>
<Text style={styles.display}>
Author: {post.author}
</Text>
<Text style={styles.display}>
Category: {post.category_name}
</Text>
<Text style={styles.display}>
Title: {post.title}
</Text>
<Text style={{overflow:'hidden'}}>
Body: {post.body}
</Text>
</View>
))
}
</ScrollView>
<View style={styles.footer}></View>
</View>
);
}
}
您必须安装 react-native-gesture-handler
和 react-navigation
。参见 this