有关[DllImport]的疑问 [英] Doubt regarding [DllImport]

问题描述

大家好，

请参阅以下代码段....

 [DllImport(" )]]
私有 静态 外部  IntPtr  hWnd，
 
是什么意思


我的疑问不仅仅在于单词DllImport :-) c#中[]的含义是什么?
解决方案
 
这意味着您正在声明方法的属性声明(因此带有"["和]"部分)，表示该方法不在.NET程序集中:它在标准的DLL文件中，在本例中为user32.dll 
 
 
这是您要导入的函数的本机位置. User32.dll是核心Windows dll之一，并且在其中实现了ShowWindow.
 
 
这是一个属性 –请参见[DllImport("user32.dll")]
private static extern Boolean ShowWindow(IntPtr hWnd, Int32 nCmdShow);

My doubt is what is mean by

[DllImport("user32.dll")]

My doubt is not simply on the word DllImport :-) What is the meaning of [] in c# ?

解决方案

It means that you are declaring an attribute to the method declaration (hence the ''['' and '']'' parts) which is saying that the method is not located in a .NET assembly: it is in a standard DLL file, in this case called user32.dll

It is the native location of the function that you are importing. User32.dll is one of the core windows dlls and ShowWindow is implemented in it.

That is an attribute – see this article[^] for a good introduction to them.

E: Attributes allow you to add declarative metadata to elements, in addition to the normal type system metadata included in the declaration itself. Attributes don''t generally do anything, they are just static information within the assembly, but various parts of the framework (including the compiler and the OS) look at some of them (e.g. [Obsolete], [Serializable], [AssemblyVersion]) and alter their behaviour accordingly.

You can create new attributes by inheriting from Attribute, but they don''t do anything – you then need to write code to inspect elements (through reflection generally) for attributes and change your logic accordingly. This can result in very elegant ''end user'' code, marking fields as e.g. columns in an output data table, or to be packaged up in a TCP message, etc, but at the cost of a bit of performance and also some rather messy code in the part of the application that manages the logic based on attributes.

[DllImport] is used by the framework to cue it on what to try to load when it resolves the method (at runtime, I think, not sure about that though).

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