Question

我已经在Reactjs中编写了以下代码，以显示来自名为from googletrans import Translator translator = Translator() with open('text.txt', 'r') as fin: text = fin.read() lst = text.split("\n") with open('spreadsheet.csv', 'w', encoding= 'UTF-8', newline='') as fout: headers = "English, Arabic, Chinese(simplified), Chinese(traditional, Finnish, French, German, Greek, Hebrew, Hindi, Irish, Italian, Japanese, Korean, Polish, Portuguese, Russian, Spanish, Turkish\n" fout.write(headers) language_lst = ['en','ar','zh-CN', 'zh-TW', 'fi', 'fr', 'de','el', 'iw', 'hi', 'ga', 'it', 'ja', 'ko', 'pl', 'pt', 'ru', 'es', 'tr'] new_lst = [] for item in lst: for i in language_lst: translated_text = translator.translate(item, dest = i) new = str(translated_text).split(",")[2].replace("text=","").strip() new_lst.append(new) counter = 0 for z in new_lst: z.encode('utf-8') fout.write(z+ ',') counter += 1 print(z) if counter % 19 == 0: fout.write('\n')的文件中名为“ data”的数组中的元素列表。我试图使显示的按钮可单击，然后在控制台上显示消息"regionData"，但我不断收到错误消息：

TypeError：无法读取未定义的属性'showSubstation'。

"Button Clicked"

Answer 1

您正在将普通函数传递给map，该函数将在没有上下文的情况下被调用，因此具有未定义的this。

render() {
    return (
        <ul>
            {regionData.data.map(function(name, i){ // <-- this function has undefined this
                //which is in turn captured by the arrow function that is created inside:
                return <tr><button onClick={ () => {this.showSubstation}}>{regionData.data[i].name}</button></tr>
            })}
        </ul>      
    );
}

一种解决方案是将this作为第二个参数传递给map，然后将其传递给回调。另一个方法是也将箭头函数用作map的参数，该函数具有词法，因此保留适当的上下文。

要注意的另一件事是this.showSubstation.bind(this)是无用的。 showSubStation是一个箭头函数，无论如何，它们都将忽略绑定的this并按词法获得this。

Answer 2

问题在于您的组件上下文（this）在map调用中未公开给您的函数。您应该改用arrow function，如下所示：

render(){
    return (
        <ul>       
          {regionData.data.map((name, i)=>{
            return <tr>
                      <button onClick={ () => {this.showSubstation}}> 
                            {regionData.data[i].name}
                      </button>
                   </tr>
          })}
        </ul>
    );
}

TypeError：尝试访问函数onClick时无法读取未定义的属性'showSubstation'

2 个答案: