Shulou(Shulou.com)06/02 Report--

Editor to share with you how to declare VB.NET Windows API function, I believe that most people do not know much about it, so share this article for your reference, I hope you will learn a lot after reading this article, let's go to know it!

VB.NET looks at the function of the icon in the file and how VB.NET declares Windows API:

For VB.NET to view icons in files, it is currently impossible to use .net FrameWork SDK alone. As mentioned earlier, it is mainly due to the short time since .net FrameWork SDK was launched, and its functionality cannot be comprehensive. The key to solve the problem is to use the Windows API function correctly, in which there are two main Windows API functions: one is to get the number of icons in the specified file; the other is to export the Windows handle of the icon from the specified location of the specified file. Both functions are located in the "Shell32.dll" file, and the entry point for both functions is "ExtractIcon". Here are the specific methods to declare these two Windows API functions in VB.NET using the DllImport feature class and the "Declare" statement, respectively.

1. Use the DllImport feature class to declare the Windows API function:

The following is a concrete example of using the DllImport feature class to declare two Windows API functions in VB.NET:

'function ExtractIcon, whose function is to export the Windows handle of the icon from the specified location of the specified file.

< System.Runtime.InteropServices.DllImport ("Shell32.dll", EntryPoint: = "ExtractIcon") > _

Public Function _ ExtractIcon (ByVal src As System.IntPtr, ByVal strFileName As string

ByVal uiIconIndex As UInt32) As System.IntPtr

End Function

'function Icon_Num, whose function is to get the number of icons in the specified file

< System.Runtime.InteropServices.DllImport ("Shell32.dll", EntryPoint: = "ExtractIcon") > _

Public Function _ Icon_Num (ByVal src As System.IntPtr, ByVal strFileName As string

ByVal uiIconIndex As Integer) As Integer

End Function

When using the DllImport feature class to declare the Windows API function, if the declared function name is the same as the entry point of the function, when VB.NET declares the Windows API function, you can omit the code that defines the entry point of the function, that is, the code corresponding to the EntryPoint object field. In this way, the code for declaring the ExtractIcon function can also be simplified as follows:

< System.Runtime.InteropServices.DllImport ("Shell32.dll") > _

Public Function _ ExtractIcon (ByVal src As System.IntPtr

ByVal strFileName As string, ByVal uiIconIndex As UInt32) As System.IntPtr

End Function

two。 Use the "Declare" statement to declare the Windows API function:

Using the "Declare" statement is indeed much easier than using the DllImport feature class. Here is how to declare the above two Windows API functions using the "Declare" statement in VB.NET:

Declare Auto Function ExtractIcon Lib "Shell32.dll" Alias "ExtractIcon"

(ByVal src As System.IntPtr, ByVal strFileName As string

ByVal uiIconIndex As UInt32) As System.IntPtr

'declare the ExtractIcon function

Declare Auto Function Icon_Num Lib "Shell32.dll" Alias "ExtractIcon"

(ByVal src As System.IntPtr, ByVal strFileName As string

ByVal uiIconIndex As Integer) As Integer

'declare the Icon_Num function

When VB.NET declares the Windows API function, the Alias keyword in the "Declare" statement is equivalent to using the EntryPoint object field in the DllImport feature class. Similarly, when using the "Declare" statement to declare a Windows API function, if the declared function and the entry point of the function are the same, you can also omit the code corresponding to the Alias keyword, so the ExtractIcon function can also be simplified as follows:

Declare Auto Function ExtractIcon Lib "Shell32.dll" (ByVal src As System.IntPtr

ByVal strFileName As string, ByVal uiIconIndex As UInt32) As System.IntPtr

These are all the contents of the article "how VB.NET declares Windows API functions". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.