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How to: Call Windows APIs (Visual Basic)

This example defines and calls the MessageBox function in user32.dll and then passes a string to it.

' Defines the MessageBox function.
Public Class Win32
    Declare Auto Function MessageBox Lib "user32.dll" (
        ByVal hWnd As Integer, ByVal txt As String,
        ByVal caption As String, ByVal Type As Integer
        ) As Integer
End Class

' Calls the MessageBox function.
Public Class DemoMessageBox
    Public Shared Sub Main()
        Win32.MessageBox(0, "Here's a MessageBox", "Platform Invoke Sample", 0)
    End Sub
End Class

This example requires:

  • A reference to the System namespace.

The following conditions may cause an exception: