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This article mainly introduces VB.NET how to use the Windows API function, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

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 VB.NET 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 VB.NET 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 Its 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, you can omit the code that defines the entry point of the function, that is, the code corresponding to the EntryPoint object field, when declaring the Windows API function. 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 'declares 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' declares Icon_Num function

When you declare the Windows API function in VB.NET, 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

The following is combined with the writing process of an example to grasp the specific use of these two Windows API functions. The purpose of this example is to read the number of icons in the specified file and display the icons in the file.

Thank you for reading this article carefully. I hope the article "how to use the Windows API function in VB.NET" shared by the editor will be helpful to everyone. At the same time, I also hope that you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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