© 2010 Autodesk
Introduction to Revit 2011 API
Implementing External Command
Show Hello World
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<VB.NET>
''  Hello World #1 - A minimum Revit external command.
<Autodesk.Revit.Attributes.Transaction(Autodesk.Revit.Attributes.TransactionMode.Automatic)> _
<Autodesk.Revit.Attributes.Regeneration(Autodesk.Revit.Attributes.RegenerationOption.Manual)> _
Public Class HelloWorld
    Implements IExternalCommand
 
    Public Function Execute( _
            ByVal commandData As Autodesk.Revit.UI.ExternalCommandData, _
            ByRef message As String, _
            ByVal elements As Autodesk.Revit.DB.ElementSet) _
            As Autodesk.Revit.UI.Result _
            Implements Autodesk.Revit.UI.IExternalCommand.Execute
 
        Autodesk.Revit.UI.TaskDialog.Show("My Dialog Title", "Hello World!")
        Return Result.Succeeded
 
    End Function
 
End Class
</VB.NET>
Task Dialog: 
Revit-style message box
to say  “Hello World”
4. Show a dialog with a message