Switch语句和等效的if-else循环始终返回错误的值。

huangapple
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英文:

Switch statement and equivalent if else loop always return wrong value

问题

我目前正在尝试使用Angular框架在文档旁边显示不同文件类型的图标。然而，无论我将文件类型设置为txt或jpg，它总是返回file-text作为图标类型的默认值。

如果我尝试进行调试，我可以看到尽管fileExtension的值是"jpg"，它却返回默认的图标类型"file-text"。

我还尝试了使用简单的if-else循环等效方法，但当我这样做时，它似乎总是对所有情况返回第一个if条件的值（例如：即使fileExtension等于"txt"，也返回"picture"）。

我真的很困惑为什么它不进入正确的case。任何帮助将不胜感激！

英文:

I am currently trying to display a different icon next to a document for different file types using Angular framework. However, no matter what file type I set as the fileExtension, be it txt or jpg as examples, it always goes to the default value of returning file-text as the iconType.

  1.     public getIcon(document: Document): string {
  2.         let mimeType = document.fileType;
  3.         let fileExtension = mimeType.split('.')[1];
  4.         let iconType = '';
  6.         switch (fileExtension) {
  7.             case fileExtension === 'jpeg' || 'gif' || 'png' || 'svg' || 'xml'  || 'bmp' || 'jpg'|| 'tif' || 'tiff':
  8.                 iconType = 'picture';
  9.                 break;
  10.             case fileExtension === 'avi' || 'mpg' || 'wmv' || 'mpeg' || 'mp4' || 'mov':
  11.                 iconType = 'video-folder';
  12.                 break;
  13.             case fileExtension === 'cda' || 'mp3' || 'mpa' || 'wav' || 'wma':
  14.                 iconType = 'volume';
  15.                 break;
  16.             case fileExtension === 'pdf' || 'ai' || 'pptx':
  17.                 iconType = 'article';
  18.                 break;
  19.             default:
  20.                 //includes: .docx , .odt, .rtf, .txt, .xml, .xps
  21.                 iconType = 'file-text';
  22.                 break;
  23.         }
  24.         console.log(iconType);
  25.         return iconType;
  26.     }

If I try debugging, I can see that despite the value of fileExtension being "jpg", it returns the default icon-type of "file-text". Image of debugging with breakpoints

I also tried using a simple if else loop equivalent but when I do that it seems to always return the first if case value for all (e.g: picture even when fileExtension = "txt"):

  1.         if (fileExtension === 'jpeg' || 'gif' || 'png' || 'svg' || 'xml' || 'bmp' || 'jpg' || 'tif' || 'tiff') {
  2.             iconType = 'picture';
  3.         } else if (fileExtension === 'avi' || 'mpg' || 'wmv' || 'mpeg' || 'mp4' || 'mov') {
  4.             iconType = 'video-folder';
  5.         } else if (fileExtension === 'cda' || 'mp3' || 'mpa' || 'wav' || 'wma') {
  6.             iconType = 'volume';
  7.         } else if (fileExtension === 'pdf' || 'ai' || 'pptx') {
  8.             iconType = 'article';
  9.         } else {
  10.             iconType = 'file-text';
  11.         }
  12.         console.log(iconType);
  13.         return iconType;

I am just really confused as to why it doesn't go to the proper case. Any help would be greatly appreciated!

答案1

得分: 1

你需要在每次条件检查的if语句中重新表述左侧，或者为每个单独的文件扩展类型在switch语句中创建一个单独的情况。

  1. if(fileExtension === "jpg" || fileExtension === "png" ...) {...}

以下还有一些其他选项，以供参考：

将每种图片类型包含在一个数组中，然后检查值是否包含在数组中：

  1. pictureFileExtensions = ["jpg", "gif", ...]
  2. videoFileExtensions = [...]
  4. if (pictureFileExtensions.includes(fileExtension)) {
  5.     iconType = "picture"
  6. } else if (videoFileExtensions.includes(fileExtension)) {
  7.     iconType = "video"
  8. } else if ...

创建一个以文件扩展名作为键，以图标类型作为值的对象：

  1. const iconTypes = {jpg: "picture", avi: "video", ...}
  3. iconType = iconTypes[fileExtension]
英文:

You need to restate the left side of your conditional check in your if statement each time; or have a separate case for each individual file extension type in your switch.

  1. if(fileExtension === “jpg” || fileExtension === “png” …) {…}

Here are a few other options as well in case you’re interested:

Include each picture type in an array, and check to see if the value is included in the array:

  1. pictureFileExtensions = [“jpg”, “gif”, …]
  2. videoFileExtensions = […]
  4. If (pictureFileExtension.includes(fileExtension)){
  5.         iconType = “picture”
  6.     } else if (videoFileExtension.includes(fileExtension)){
  7.         iconType = “video”
  8.     } else if …

Create an object with the file extension as the key and the icon type as the value:

  1. const iconTypes = {jpg: “picture”, avi: “video”, …}
  3. iconType = iconType[fileExtension]

答案2

得分: 0

你实际上在使用 switch case 时出现了错误。以下是正确的语法：

  1. switch (fileExtension) {
  2.     case 'jpeg':
  3.     case 'gif':
  4.     case 'png':
  5.     case 'svg':
  6.     case 'xml':
  7.     case 'bmp':
  8.     case 'jpg':
  9.     case 'tif':
  10.     case 'tiff':
  11.         iconType = 'picture';
  12.         break;
  13.     case 'avi':
  14.     case 'mpg':
  15.     case 'wmv':
  16.     case 'mpeg':
  17.     case 'mp4':
  18.     case 'mov':
  19.         iconType = 'video-folder';
  20.         break;
  21.     case 'cda':
  22.     case 'mp3':
  23.     case 'mpa':
  24.     case 'wav':
  25.     case 'wma':
  26.         iconType = 'volume';
  27.         break;
  28.     case 'pdf':
  29.     case 'ai':
  30.     case 'pptx':
  31.         iconType = 'article';
  32.         break;
  33.     default:
  34.         // 包括：.docx，.odt，.rtf，.txt，.xml，.xps
  35.         iconType = 'file-text';
  36.         break;
  37. }
英文:

You're actually using the switch case wrong. Here is the correct syntax:

  1.     switch (fileExtension) {
  2.         case 'jpeg':
  3.         case 'gif':
  4.         case 'png':
  5.         case 'svg':
  6.         case 'xml':
  7.         case 'bmp':
  8.         case 'jpg':
  9.         case 'tif':
  10.         case 'tiff':
  11.             iconType = 'picture';
  12.             break;
  13.         case 'avi':
  14.         case 'mpg':
  15.         case 'wmv':
  16.         case 'mpeg':
  17.         case 'mp4':
  18.         case 'mov':
  19.             iconType = 'video-folder';
  20.             break;
  21.         case 'cda':
  22.         case 'mp3':
  23.         case 'mpa':
  24.         case 'wav':
  25.         case 'wma':
  26.             iconType = 'volume';
  27.             break;
  28.         case 'pdf':
  29.         case 'ai':
  30.         case 'pptx':
  31.             iconType = 'article';
  32.             break;
  33.         default:
  34.             //includes: .docx , .odt, .rtf, .txt, .xml, .xps
  35.             iconType = 'file-text';
  36.             break;
  37.     }

huangapple
  • 本文由 发表于 2023年6月19日 12:30:31
  • 转载请务必保留本文链接：https://go.coder-hub.com/76503615.html
  • angular
  • if-statement
  • switch-statement
  • typescript
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