Javascript (Expo)从服务器获取数据后,响应本机不更新状态
我正在用react native创建一个应用程序。我在应用程序中遇到一个问题。我正在从服务器获取数据,并用获取的数据更新我的状态。来自服务器的数据在控制台日志记录中没有任何错误。但是,在设置状态后,react native不会在屏幕上重新呈现我的问题。但当我从代码编辑器中保存项目并重新加载expo时,数据(问题)就会显示在屏幕上。我找不到解决方案,也找不到发生错误的地方。希望下面的代码和gif演示我的问题。Javascript (Expo)从服务器获取数据后,响应本机不更新状态,javascript,reactjs,react-native,expo,Javascript,Reactjs,React Native,Expo,我正在用react native创建一个应用程序。我在应用程序中遇到一个问题。我正在从服务器获取数据,并用获取的数据更新我的状态。来自服务器的数据在控制台日志记录中没有任何错误。但是,在设置状态后,react native不会在屏幕上重新呈现我的问题。但当我从代码编辑器中保存项目并重新加载expo时,数据(问题)就会显示在屏幕上。我找不到解决方案,也找不到发生错误的地方。希望下面的代码和gif演示我的问题。 我已经从代码中删除了一些样式以减少长度,但代码仍然很长。可以在此处找到原始文件(代码
我已经从代码中删除了一些样式以减少长度,但代码仍然很长。可以在此处找到原始文件(代码)的链接
import React,{useffect,useState}来自“React”;
从“react native multiple choice picker”导入MultipleChice;
进口{
看法
文本,
(其他进口),
按钮
}从“反应本族语”;
从“./加载”导入加载屏幕;
从“../../config/firebase”导入firebase;
从“../../config/variable”导入服务器;
常量解决方案=({route,navigation})=>{
const[isLoading,setIsLoading]=useState(false);
const[questionData,setQuestionData]=useState([]);
const[correctAnswer,setCorrectAnswer]=useState([]);
常量[ErrorAnswer,SetErrorAnswer]=useState([]);
const[notAttempted,setNotAttempted]=useState([]);
常量[questionCount,setQuestionCount]=useState(0);
const[allQuestion,setAllQuestion]=useState([]);
const{examid}=route.params;
const fetchSolution=async()=>{
设置加载(真);
试一试{
const response=wait fetch(`${SERVER}admin/get/result for user`{
方法:“张贴”,
标题:{
接受:“应用程序/json”,
“内容类型”:“应用程序/json”,
},
正文:JSON.stringify({
电子邮件:firebase.auth().currentUser.email,
examid,
}),
});
const responseData=await response.json();
设置问题数据(应答数据);
setCorrectAnswer(wait JSON.parse(responseData.result[0].correctAnsArr));
const data1=JSON.parse(responseData.result[0].ErrorAnsarr);
设置错误答案(数据1);
setNotAttempted(等待JSON.parse(responseData.result[0].notAttemtedArr));
const datafinal=wait updateQuestion();
设置所有问题(最终数据);
}捕获(错误){
console.log(错误);
警报。警报(“服务器错误”);
}
设置加载(假);
};
常量updateQuestion=()=>{
var correctAnsArr=[];
var=var[];
var notAttemtedArr=[];
for(设i=0;i{
fetchSolution();
}, []);
const RenderQuestion=()=>{
返回(
{allQuestion.length>0(
问题{allQuestion.length}中的问题{questionCount+1}
{allQuestion[questionCount]。isQuestionImage==“1”(
) : (
{allQuestion[questionCount].questionText}
)}
) : (
没有数据
)}
);
};
常量渲染=()=>{
返回(
{allQuestion.length>0(
{allQuestion[questionCount].isOptionImage==“1”(
) : (
)}
) : (
)}
);
};
常量渲染按钮=()=>{
返回(
{问题计数!=0(
{
setQuestionCount(()=>questionCount-1);
}}
/>
):null}
{questionCount+1questionCount+1);
}}
/>
):null}
navigation.navigate(“结果列表”)}
/>
);
};
如果(孤岛加载){
返回;
}
返回(
);
};
导出默认解决方案;
在updateQuestion()
函数中,将填充为allQuestion
的内容,您希望正确答案、问题数据,
状态保存他们在fetchSolution()
中获得的数据
问题是,setState
函数是异步调用,当您进入updateQuestion()
,从fetchSolution()
内部进入时,状态并不是您期望的状态
添加一个示例,说明使用useffect
等待更改如何影响状态,然后才会触发操作
需要明确的是,问题是在第一次渲染时运行
useffect
之后,
import React, { useEffect, useState } from "react";
import MultipleChoice from "react-native-multiple-choice-picker";
import {
View,
Text,
(other imports),
Button,
} from "react-native";
import LoadingScreen from "../Loading";
import firebase from "../../config/firebase";
import SERVER from "../../config/variable";
const Solution = ({ route, navigation }) => {
const [isLoading, setIsLoading] = useState(false);
const [questionData, setQuestionData] = useState([]);
const [correctAnswer, setCorrectAnswer] = useState([]);
const [wrongAnswer, setWrongAnswer] = useState([]);
const [notAttempted, setNotAttempted] = useState([]);
const [questionCount, setQuestionCount] = useState(0);
const [allQuestion, setAllQuestion] = useState([]);
const { examid } = route.params;
const fetchSolution = async () => {
setIsLoading(true);
try {
const response = await fetch(`${SERVER}admin/get/result-for-user`, {
method: "POST",
headers: {
Accept: "Application/json",
"Content-Type": "Application/json",
},
body: JSON.stringify({
email: firebase.auth().currentUser.email,
examid,
}),
});
const responseData = await response.json();
setQuestionData(responseData.data);
setCorrectAnswer(await JSON.parse(responseData.result[0].correctAnsArr));
const data1 = JSON.parse(responseData.result[0].wrongAnsArr);
setWrongAnswer(data1);
setNotAttempted(await JSON.parse(responseData.result[0].notAttemtedArr));
const datafinal = await updateQuestion();
setAllQuestion(datafinal);
} catch (error) {
console.log(error);
Alert.alert("Server Error");
}
setIsLoading(false);
};
const updateQuestion = () => {
var correctAnsArr = [];
var wrongAnsArr = [];
var notAttemtedArr = [];
for (let i = 0; i < correctAnswer.length; i++) {
for (let j = 0; j < questionData.length; j++) {
if (correctAnswer[i].questionId === questionData[j].id) {
questionData[j].selectedOption = correctAnswer[i].selectedOption;
correctAnsArr.push(questionData[j]);
}
}
}
for (let i = 0; i < wrongAnswer.length; i++) {
for (let j = 0; j < questionData.length; j++) {
if (wrongAnswer[i].questionId === questionData[j].id) {
questionData[j].selectedOption = wrongAnswer[i].selectedOption;
wrongAnsArr.push(questionData[j]);
}
}
}
for (let i = 0; i < notAttempted.length; i++) {
for (let j = 0; j < questionData.length; j++) {
if (notAttempted[i].questionId === questionData[j].id) {
questionData[j].selectedOption = notAttempted[i].selectedOption;
notAttemtedArr.push(questionData[j]);
}
}
}
return [...correctAnsArr, ...wrongAnsArr, ...notAttemtedArr];
};
useEffect(() => {
fetchSolution();
}, []);
const RenderQuestion = () => {
return (
<View>
<View>
{allQuestion.length > 0 ? (
<View
key={allQuestion[0].id}
style={{
width: Dimensions.get("window").width,
}}
>
<View style={{ margin: 10 }}>
<Text style={{ fontSize: 16 }}>
Question {questionCount + 1} of {allQuestion.length}
</Text>
</View>
{allQuestion[questionCount].isQuestionImage === "1" ? (
<View
style={{
width: Dimensions.get("window").width,
display: "flex",
flex: 1,
justifyContent: "center",
alignItems: "center",
}}
>
<Image
style={{
height: Dimensions.get("window").height * 0.5,
width: Dimensions.get("window").width * 0.8,
}}
source={{
uri: allQuestion[questionCount].questionFile,
}}
/>
</View>
) : (
<View>
<Text style={{ fontSize: 35, margin: 15 }}>
{allQuestion[questionCount].questionText}
</Text>
</View>
)}
<RenderOption />
</View>
) : (
<View>
<Text>No Data</Text>
</View>
)}
</View>
</View>
);
};
const RenderOption = () => {
return (
<View>
{allQuestion.length > 0 ? (
<View>
{allQuestion[questionCount].isOptionImage === "1" ? (
<MultipleChoice
direction={"column"}
chosenIndex={allQuestion[questionCount].selectedOption}
choices={[
<Image
style={{
height: Dimensions.get("window").height * 0.3,
width: Dimensions.get("window").width * 0.6,
}}
source={{
uri: allQuestion[questionCount].optionAFile,
}}
/>,
<Image
style={{
height: Dimensions.get("window").height * 0.3,
width: Dimensions.get("window").width * 0.6,
}}
source={{
uri: allQuestion[questionCount].optionBFile,
}}
/>,
<Image
style={{
height: Dimensions.get("window").height * 0.3,
width: Dimensions.get("window").width * 0.6,
}}
source={{
uri: allQuestion[questionCount].optionCFile,
}}
/>,
<Image
style={{
height: Dimensions.get("window").height * 0.3,
width: Dimensions.get("window").width * 0.6,
}}
source={{
uri: allQuestion[questionCount].optionDFile,
}}
/>,
]}
/>
) : (
<MultipleChoice
direction={"column"}
chosenIndex={allQuestion[questionCount].selectedOption}
choices={[
<Text>
{allQuestion[questionCount].optionAText}
</Text>,
<Text>
{allQuestion[questionCount].optionBText}
</Text>,
<Text>
{allQuestion[questionCount].optionCText}
</Text>,
<Text>
{allQuestion[questionCount].optionDText}
</Text>,
]}
/>
)}
</View>
) : (
<View></View>
)}
</View>
);
};
const Renderbutton = () => {
return (
<View>
{questionCount != 0 ? (
<View>
<Button
color="#f9a602"
title="Prev"
onPress={() => {
setQuestionCount(() => questionCount - 1);
}}
/>
</View>
) : null}
{questionCount + 1 < allQuestion.length ? (
<View>
<Button
title="Next"
onPress={() => {
setQuestionCount(() => questionCount + 1);
}}
/>
</View>
) : null}
<View>
<Button
color="red"
title="Finish"
onPress={() => navigation.navigate("ResultList")}
/>
</View>
</View>
);
};
if (isLoading) {
return <LoadingScreen />;
}
return (
<SafeAreaView style={{ display: "flex", flex: 1 }}>
<ImageBackground
source={require("../../images/signup_screen.jpg")}
style={{ flex: 1, resizeMode: "cover" }}
>
<View>
<ScrollView>
<RenderQuestion />
<Renderbutton />
</ScrollView>
</View>
</ImageBackground>
</SafeAreaView>
);
};
export default Solution;
const Solution = ({ route, navigation }) => {
const [questionData, setQuestionData] = useState([]);
const [correctAnswer, setCorrectAnswer] = useState([]);
const [allQuestion, setAllQuestion] = useState([]);
const fetchSolution = async () => {
setQuestionData(['something'])
setCorrectAnswer(['something'])
}
useEffect(() => fetchSolution(), []);
useEffect(() => correctAnswer.length && questionData.length &&
updateQuestion(), [correctAnswer, questionData]);