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.

Example

' 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

Compile the code

This example requires:

• A reference to the System namespace.

Robust Programming

The following conditions may cause an exception:

• The method is not static, is abstract, or has been previously defined. The parent type is an interface, or the length of name or dllName is zero. (ArgumentException)

• The name or dllName is Nothing. (ArgumentNullException)

• The containing type has been previously created using CreateType. (InvalidOperationException)

See also

• A Closer Look at Platform Invoke
• Platform Invoke Examples
• Consuming Unmanaged DLL Functions
• Defining a Method with Reflection Emit
• Walkthrough: Calling Windows APIs
• COM Interop