Using the Windows API in VB.NET

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We have been using Windows APIs to get the most out of the Windows operating system. Sites like www.vbapi.com have always been my favorite hangouts for understanding and using APIs.

.NET extends its support for using Windows APIs. Let's check out how we can use the MessageBox API to display a simple MessageBox.

We will be using the DLLImport attribute for Platform Invoke (Pinvoke) service, which is used to tell the runtime that the code being executed is unmanaged code.

Class TestAPI.vb

Imports system
Imports System.Runtime.InteropServices

PublicClass TestAPI
  SharedSub main()
  ' Display a messagebox using the Win32 API
    API.MessageBox(0, "API Message Box", "Win32 API", 0)
  EndSub

EndClass

'Class that will expose the Win32 API 
PublicClass API

 ' Declare the external Win32 API function
 ' BETA 2 requires the <DLLimport> attribute before the function  signature.

<DLLimport("user32.dll")>PublicSharedFunction MessageBox(ByVal HwndAsInteger, _
ByVal [text]AsString, _
ByVal CaptionAsString, _
ByVal ypeAsInteger)AsInteger

EndFunction
EndClass

Compile the class as Vbc testapi.vb /r:system.dll. When we execute the testapi.exe we will see a MessageBox being popped up.