Question

I’m trying to convert the following C# code to VB. The reults from online conversion pages I have tried doesn’t make sense to me and VS2010 marks them as flawed. My limited C# knowledge about events isn’t enough to solve this one…

The MVVM sample uses this interface:

public interface IRequestCloseViewModel
{
  event EventHandler RequestClose
} 

And it is used in this base class:

public class ApplicationWindowBase : Window
{
    public ApplicationWindowBase()
    {
        this.DataContextChanged += new DependencyPropertyChangedEventHandler(this.OnDataContextChanged);
    }

    private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue is IRequestCloseViewModel)
        {
              // if the new datacontext supports the IRequestCloseViewModel we can use
              // the event to be notified when the associated viewmodel wants to close
              // the window
             ((IRequestCloseViewModel)e.NewValue).RequestClose += (s, e) => this.Close();
        }
    }
} 

What would the correct VB .NET translation look like?

Answer 1

This should do it for you:

Public Interface IRequestCloseViewModel

    //Event RequestClose As EventHandler
    Event RequestClose(ByVal sender As Object, ByVal e As EventArgs)

End Interface

Public Class ApplicationWindowBase
    Inherits Window

    Public Sub New()
        AddHandler Me.DataContextChanged, AddressOf OnDataContextChanged
    End Sub

    Private Sub OnDataContextChanged(ByVal sender As Object, ByVal e As DependencyPropertyChangedEventArgs)

        Dim request = TryCast(e.NewValue, IRequestCloseViewModel)

        If request IsNot Nothing Then
            AddHandler request.RequestClose, Sub(sender, event) Me.Close
            //Bear in mind you cannot do Sub(x,y) in VS pre 2010    
        End If

    End Sub

End Class