Question

I am trying to update a label from one form to another. the code is compiling fine but not updating?

Class MainWindow 

    Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
        Dim frm As New Window1
        frm.Show()
    End Sub
End Class

second form:

Public Class Window1

    Private Sub Button1_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles Button1.Click
        My.Windows.MainWindow.Label1.Content = "dsfdsfsdf"
        My.Windows.MainWindow.Label1.UpdateLayout()
    End Sub
End Class

it doesn’t update the main form’s label… hope that makes it clearer

Answer 1

So here’s the code that you actually need:

Public Class Window1

Private Sub Button1_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles Button1.Click
    DirectCast(Application.Current.MainWindow, MainWindow).Label1.Content = "test"
End Sub

End Class

I’m not sure what the My.Windows collection is, but the Application.MainWindow gives you a reference to the window that is set as the start up object in the project properties (or the one you set in your app.xaml.cs file). Previously you were probably getting a reference to a different instance of the Window1 class, hence it was running and not throwing an exceptions, but since it wasn’t the actual visible instance of the window then you didn’t see any changes.