在C＃中嵌套使用语句

系统管理员 2023-03-06 08:15 2阅读 0赞

本文翻译自：[Nested using statements in C\#][Nested using statements in C]

*I am working on a project.* **我正在做一个项目。** *I have to compare the contents of two files and see if they match each other precisely.* **我必须比较两个文件的内容，看看它们是否精确匹配。**

*Before a lot of error-checking and validation, my first draft is:* **在进行大量错误检查和验证之前，我的初稿是：**

DirectoryInfo di = new DirectoryInfo(Environment.CurrentDirectory + "\\TestArea\\");
      FileInfo[] files = di.GetFiles(filename + ".*");
    
      FileInfo outputFile = files.Where(f => f.Extension == ".out").Single<FileInfo>();
      FileInfo expectedFile = files.Where(f => f.Extension == ".exp").Single <FileInfo>();
    
      using (StreamReader outFile = new StreamReader(outputFile.OpenRead()))
      {
        using (StreamReader expFile = new StreamReader(expectedFile.OpenRead()))
        {
          while (!(outFile.EndOfStream || expFile.EndOfStream))
          {
            if (outFile.ReadLine() != expFile.ReadLine())
            {
              return false;
            }
          }
          return (outFile.EndOfStream && expFile.EndOfStream);
        }
      }

*It seems a little odd to have nested `using` statements.* **嵌套`using`语句似乎有点奇怪。**

*Is there a better way to do this?* **有一个更好的方法吗？**

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### \#1楼 ###

参考：[https://stackoom.com/question/5zVp/在C-中嵌套使用语句][https_stackoom.com_question_5zVp_C-]

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### \#2楼 ###

*If the objects are of the **same type** you can do the following* **如果对象属于同一类型 ，则可以执行以下操作**

using (StreamReader outFile = new StreamReader(outputFile.OpenRead()), 
                        expFile = new StreamReader(expectedFile.OpenRead()))
    {
        // ...
    }

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### \#3楼 ###

*There's nothing odd about it.* **它没什么奇怪的。** *`using` is a shorthand way of ensuring the disposal of the object once the code block is finished.* **`using`是一种在代码块完成后确保处理对象的简便方法。** *If you have a disposable object in your outer block that the inner block needs to use, this is perfectly acceptable.* **如果您的外部块中有一个一次性物体，内部块需要使用，这是完全可以接受的。**

*Edit: Too slow on the typing to show consolidated code example.* **编辑：输入太慢以显示合并代码示例。** *+1 to everyone else.* **+1给其他人。**

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### \#4楼 ###

*When the `IDisposable` s are of the same type, you can do the following:* **当`IDisposable`的类型相同时，您可以执行以下操作：**

using (StreamReader outFile = new StreamReader(outputFile.OpenRead()), 
         expFile = new StreamReader(expectedFile.OpenRead()) {
         // ...
     }

*The MSDN page on [`using`][using] has documentation on this language feature.* **在MSDN页面[`using`][using]了这种语言功能的文档。**

*You can do the following whether or not the `IDisposable` s are of the same type:* **无论`IDisposable`是否属于同一类型，您都可以执行以下操作：**

using (StreamReader outFile = new StreamReader(outputFile.OpenRead()))
    using (StreamWriter anotherFile = new StreamReader(anotherFile.OpenRead()))
    { 
         // ...
    }

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### \#5楼 ###

*You can group multiple disposable objects in one using-statement with commas:* **您可以使用逗号将多个一次性对象组合在一个using语句中：**

using (StreamReader outFile = new StreamReader(outputFile.OpenRead()), 
           expFile = new StreamReader(expectedFile.OpenRead()))
    {
    
    }

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### \#6楼 ###

*The preferred way to do this is to only put an opening brace `{` after the last `using` statement, like this:* **执行此操作的首选方法是仅在最后一个`using`语句之后放置一个大括号`{` ，如下所示：**

using (StreamReader outFile = new StreamReader(outputFile.OpenRead()))
    using (StreamReader expFile = new StreamReader(expectedFile.OpenRead())) 
    {
        ///...
    }

[Nested using statements in C]: https://oldbug.net/q/5zVp/Nested-using-statements-in-C
[https_stackoom.com_question_5zVp_C-]: https://stackoom.com/question/5zVp/%E5%9C%A8C-%E4%B8%AD%E5%B5%8C%E5%A5%97%E4%BD%BF%E7%94%A8%E8%AF%AD%E5%8F%A5
[using]: http://msdn.microsoft.com/en-us/library/yh598w02.aspx