主頁 > 後端開發 > React陣列狀態更新不一致

React陣列狀態更新不一致

2022-01-12 04:01:14 後端開發

遇到一個奇怪的問題，希望有人能幫忙。我試圖通過一系列單詞和標點符號“迭代”，以使滾動對話出現。我有這個作業，除了當我嘗試將它推送到 React 時，它只是……亂七八糟。這是我所擁有的：


export default function DialogueBox(params){

    const params="The story, characters, and events, in this game are entirely fictional. Any similarities to actual people, places and events are entirely coicidental.";

    let dialogueValue = [];

    let [dialogue, setDialogue] = useState([]);
  
    let letterArray = params.text.split(/\b/);

    const handleChangeValue = text => {
       
                const updatedLettersArray = [...dialogueValue, text];
                console.log('updated: '   updatedLettersArray);
                // setDialogue(oldArray=>[...oldArray,updatedLettersArray]);
                
    }

    return (
        <div className="dialogueBox">
            {letterArray.forEach(function(element,index){
                setTimeout(
                    function(){
                        handleChangeValue(element);
                        dialogueValue.push(element);
                    }, index * 500
                );
            })}
            <p>{dialogue}</p>
        </div>
    )
}

這是控制臺日志，這是正確的：

updated: The DialogueBox.js:15
updated: The, DialogueBox.js:15
updated: The, ,story DialogueBox.js:15
updated: The, ,story,, DialogueBox.js:15
updated: The, ,story,, ,characters DialogueBox.js:15
updated: The, ,story,, ,characters,, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are, ,entirely DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are, ,entirely, DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are, ,entirely, ,coicidental DialogueBox.js:15
updated: The, ,story,, ,characters,, ,and, ,events,, ,in, ,this, ,game, ,are, ,entirely, ,fictional,. ,Any, ,similarities, ,to, ,actual, ,people,, ,places, ,and, ,events, ,are, ,entirely, ,coicidental,.

但是，如果我取消注釋該行

// setDialogue(oldArray=>[...oldArray,updatedLettersArray]);

發生以下情況：

updated: The 94 DialogueBox.js:15
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updated: The, ,story DialogueBox.js:15
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基本上只是不停地重復自己。我很肯定我在這里遺漏了一些明顯的東西，但我很茫然！謝謝大家的幫助

uj5u.com熱心網友回復：

使用setInterval和index來跟蹤位置。在此處查看示例https://codesandbox.io/s/bold-wind-sq8lb?file=/src/App.js：

import { useEffect, useState } from "react";

export default function App() {
  const sentence =
    "The story, characters, and events, in this game are entirely fictional. Any similarities to actual people, places and events are entirely coicidental.";

  const [dialogue, setDialogue] = useState("");
  const [index, setIndex] = useState(0);
  const letterArray = sentence.split(/\b/);

  const handleChangeValue = () => {
    if (letterArray[index] !== undefined) {
      setDialogue((dialogue) => dialogue   letterArray[index]);
    }
  };

  useEffect(() => {
    // update the dialogue here
    const interval = setInterval(() => {
      if (index < letterArray.length) {
        setIndex((index) => index   1);
      }
    }, 100);
    return () => clearInterval(interval);
  });

  useEffect(() => {
    // update the dialogue here
    handleChangeValue();
    console.log(`New dialogue: ${dialogue}`);
  }, [index]);

  return (
    <div className="App">
      <p>{dialogue}</p>
    </div>
  );
}

uj5u.com熱心網友回復：

不要直接在 React 組件回傳中使用 setTimeout，它會在 Javascript 運行時設定大量計時器并且永遠不會被回收。

如果 setTimeout 甚至 setInterval 是您所需要的，那么用 useEffect 將它們包裝起來就是個好主意

通過猜測你想要做什么，這是一個示例代碼。它將每 0.5 秒在螢屏上顯示一個單詞，直到 params 結束

export default function DialogueBox(params){

  const params = "The story, characters, and events, in this game are entirely fictional. Any similarities to actual people, places and events are entirely coicidental.";
  const letters = params.split(/\b/)

  const [dialogue, setDialogue] = useState([]);

  useEffect(() => {
    const timers = []

    letters.forEach((letter, index) => {
      timers.push(
        setTimeout(() => {
          console.log(`Display at 500*${index} ms: ${letter}`)
          setDialogue(originDialogue => [...originDialogue, letter])
        }, 500*index)
      )
    })

    return () => timers.map((timer) => clearTimeout(timer))  // clean up timers to prevent memory leak
  }, [params]) // params here as dependency of useEffect, see offical document for useEffect for detail

  return (
    <div className="dialogueBox">
      {dialogue.map((letter) => (
        <p>{letter}</p>
      ))}
    </div>
  )
}

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