React - 防止所有子组件安装在负载上

Question

我正在尝试创建一个单页 React 应用程序，一次安装某些组件。相反，所有组件都是一次性加载的。

我发现的有关安装组件的 StackOverflow 帖子是关于防止它们在更改时重新渲染的。我有 3 个部分，但我只希望其中一个部分出现在页面加载时。我希望计时器首先出现。当按下开始按钮时，我希望出现问题。最后，当计时器归零或用户按下提交按钮时，结果就会出现。各个组件都按我想要的方式工作，但我想隐藏它们直到它们被调用。仅供参考 - (selectedOption) 来自 React-Select 依赖项。

仓库： https: //github.com/irene-rojas/pixar-react

应用程序

import React, { Component } from 'react';
import './App.css';
import Timer from "./Timer";
import Questions from "./Questions/Questions.js";
import Results from "../src/Results";

class App extends Component {

state = {
    totalTrue: 0,
    totalFalse: 0,
}

componentDidMount() {
    return (
        <Timer />
    )
}

// submit button
handleFormSubmit = event => {
    event.preventDefault();
    console.log("submit button clicked");
        return (
            <Results />
        )
};

callbackHandlerFunction = ( selectedOption ) => {
    const answerValue = selectedOption.value;
    if (answerValue === true) {
        this.setState({totalTrue: this.state.totalTrue + 1}, () => {
            console.log(`New TotalTrue: ${this.state.totalTrue}`);
        });
    };
    if (answerValue === false) {
        this.setState({totalFalse: this.state.totalFalse + 1}, () => {
            console.log(`New TotalFalse: ${this.state.totalFalse}`);
        });
    };
  } 

  render() {
    return (

  <div className="parallax">

    <div className="App">

        <div className="wrapper">

        <div className="headerDiv">
            <h1>Pixar Trivia!</h1>
        </div>

        <div className="timerDiv">
            <Timer />   
        </div>

        <div className="questionSection">
            <Questions 
                handleClickInParent={this.callbackHandlerFunction} 
            />

            <div>
                <button onClick={this.handleFormSubmit}>Submit</button>
            </div>
        </div>



        {/* this code will hide Results until these conditions are met. This was an experiment to see if anything hid Results from mounting on load */}
        {this.state.totalTrue >= 8 && this.state.totalFalse >= 8 &&
        <div className="resultsDiv">
            <Results 
                totalTrue={this.state.totalTrue}
                totalFalse={this.state.totalFalse}
            />
        </div>
        }      
        </div>

    </div>

  </div>
   );
  }
}

export default App;

计时器

import React, { Component } from 'react';

class Timer extends Component {

  state = {
timer: 10
  };

  startTimer = () => {
    this.timer = setInterval(() => this.setState({
    timer: this.state.timer - 1}), 1000); 
    // onClick, load Questions
    // but do I need to import Questions?
   };

  stopTimer = () => {
    clearInterval(this.timer);
    alert("Time's up!");
    // when this.state.timer === 0, load Results
    // do I need to import Results?
  };

  render() {
    return (
      <div className="Timer">
        <div>{this.state.timer} seconds</div>
        <button onClick={this.startTimer}>Start!</button>
        {this.state.timer === 0 && this.stopTimer()}
      </div>
    );
  }
}

export default Timer;

Answer 1

您应该研究条件渲染。默认情况下，您的应用程序render()具有所有子组件。您要么想要将它们设置为隐藏，要么根本不渲染它们。

例如

{conditionToMeet &&
 <div>
    content to render here
 </div>
}