如何显示React JS中函数返回的内容？

问题描述

我是新来回应JS的人。 我想在单击“检查统计信息”按钮后显示图形。我可以看到我的函数正在执行，但是如何显示返回的函数呢？由于handleShowStatistics（）是一个函数，因此我无法编写render（）方法。 这是我的“ Quiz.js”代码

import React,{ Component } from "react";
import { Link } from "react-router-dom";
import "./style.css";
import QuestionBank from "./QuestionBank.js";
import { Pie } from "react-chartjs-2";

class Quiz extends Component {
  constructor(props) {
    super(props);
    this.state = {
      userAnswer: null,currentIndex: 0,options: [],data: [],quizEnd: false,score: 0,disabled: true
    };
  }

  loadQuiz = () => {
    const { currentIndex } = this.state;
    this.setState(() => {
      return {
        question: QuestionBank[currentIndex].question,options: QuestionBank[currentIndex].options,answer: QuestionBank[currentIndex].answer
      };
    });
  };

  nextQuestionHandler = () => {
    const { userAnswer,answer,score } = this.state;

    if (userAnswer === answer) {
      this.setState({
        score: score + 1
      });
    }
    this.setState({
      currentIndex: this.state.currentIndex + 1,userAnswer: null
    });
  };

  previosQuestionHandler = () => {
    // const{userAnswer}=this.state
    this.setState({
      currentIndex: this.state.currentIndex - 1,userAnswer: null
    });
  };

  componentDidMount() {
    this.loadQuiz();
  }

  checkAnswer = (answer) =>
    this.setState({
      userAnswer: answer,disabled: false
    });

  finishHandler = () => {
    const { userAnswer,score } = this.state;
    if (userAnswer === answer) {
      this.setState({
        score: score + 1
      });
    }
    if (this.state.currentIndex === QuestionBank.length - 1) {
      this.setState({
        quizEnd: true
      });
    }
  };

  attemptAnotherTry = () => {
    this.loadQuiz();
    this.setState({
      userAnswer: null,disabled: true
    });
  };

  handleShowStatistics = () => {
    console.log("fucntion start");
    const { data } = this.state;
    this.setState({
      data: [
        {
          labels: ["Correct Answers","Incorrect Answers"],datasets: [
            {
              label: "statistical chart",data: [this.state.score,6 - this.state.score],backgroundColor: ["rgba(255,99,132,1)","rgba(255,205,86,1)"]
            }
          ]
        }
      ]
    });
    console.log("fucntion end");

    return (
      <div>
        <div
          style={{
            width: "1000px",height: "1000px",textAlign: "center",marginLeft: "250px"
          }}
        >
          {/* <Pie data={data} options={options}/> */}
          <Pie data={data} />
          <Link to="/Test" style={{ textAlign: "center" }}>
            Attempt test again
          </Link>
        </div>
      </div>
    );
    
  };

  componentDidUpdate(prevProps,prevState) {
    const { currentIndex } = this.state;
    if (this.state.currentIndex !== prevState.currentIndex) {
      this.setState(() => {
        return {
          disabled: true,question: QuestionBank[currentIndex].question,answer: QuestionBank[currentIndex].answer
        };
      });
    }
  }

  render() {
    const { question,options,currentIndex,userAnswer,quizEnd } = this.state;
    if (quizEnd) {
      return (
        <div className="containerBox">
          <h1> Game Over. Final score is {this.state.score} points</h1>
          <p> The correct answers for the quiz are</p>
          <ul>
            {QuestionBank.map((item,index) => (
              <li className="options" key={index}>
                {item.answer}
              </li>
            ))}
          </ul>
          {currentIndex === QuestionBank.length - 1 && (
            <button
              className="attemptButton"
              onClick={this.attemptAnotherTry}
              disabled={this.state.disabled}
            >
              Retest?
            </button>
          )}

          {currentIndex === QuestionBank.length - 1 && (
            <button onClick={this.handleShowStatistics}>
              Check Statistics
            </button>
          )}
          {/* <globalThis.pieChart/> */}
        </div>
      );
    }
    return (
      <div className="containerBox">
        <div className="title">Quiz </div>
        <h2>{question}</h2>
        <span>{`Question ${currentIndex + 1} of ${QuestionBank.length}`}</span>
        {options.map((option) => (
          <p
            key={option.id}
            className={`options ${userAnswer === option ? "selected" : null}`}
            onClick={() => this.checkAnswer(option)}
          >
            {option}
          </p>
        ))}

        {currentIndex < QuestionBank.length - 1 && (
          <button
            disabled={this.state.disabled}
            onClick={this.nextQuestionHandler}
          >
            Next Question
          </button>
        )}
        {currentIndex < QuestionBank.length - 1 && currentIndex > 0 && (
          <button
            onClick={this.previosQuestionHandler}
            className="previousQuestion"
          >
            Previous Question
          </button>
        )}
        {currentIndex === QuestionBank.length - 1 && (
          <button onClick={this.finishHandler} disabled={this.state.disabled}>
            Finish
          </button>
        )}
      </div>
    );
  }
}

export default Quiz;

请帮助我解决问题。我真的被困在这里，努力显示图表。

解决方法

在渲染中，您可以检查是否有数据并在此处显示统计信息

return (
<div className="containerBox">
   {this.state.data && <Statistics data={this.state.data}/>}
   ...
</div>
)

假设您定义了一个组件统计信息以显示数据

调用setState函数将自动调用render方法

,

如果使用单击检查统计信息按钮，则可以将标志状态设置为true。因此，只有在checkStatistics id为true时，它才会出现。

沙盒https://codesandbox.io/s/patient-rgb-z5tkj?file=/src/App.js

类似的东西：

 class App extends Component {
   constructor(props) {
     super(props);
     this.state = {
       data: [],checkStatistics: false
     };
   }

  handleShowStatistics = () => {
    console.log("fucntion start");
    const { checkStatistics } = this.state;
    this.setState({
      checkStatistics: !checkStatistics
    });
    console.log("fucntion end");
  };

  render() {
    const { checkStatistics } = this.state;

    return (
      <div className="containerBox">
        <div className="title">Quiz</div>
        <h2>Question</h2>
        <button onClick={this.handleShowStatistics}>Check Statistics</button>
        {checkStatistics && (
          <div
            style={{
              width: "100px",height: "100px",textAlign: "center",marginLeft: "25px"
            }}
          >
            Show this div if checkStatistics is true
          </div>
        )}
      </div>
    );
  }
}

export default App;