Question

I have a new VB.Net WPF application. The MainWindow.xaml contains nothing more than a single ‘test’ button:

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button Content="Test"
                Name="btnTest" />
    </Grid>
</Window>

The Application.xaml is untouched:

<Application x:Class="Application"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="MainWindow.xaml">
    <Application.Resources>

    </Application.Resources>
</Application>

The code behind is shown here. All I did was double click the button so the event handler is added automatically. I have also added the MainWindow to the View namespace.

Namespace View
    Class MainWindow
        ' A test button on the main window
        Private Sub btnTest_Click(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles btnTest.Click
            MessageBox.Show("Hello world!")
        End Sub
    End Class
End Namespace

When I build this it doesn’t compile. Error message that I get is:

Handles clause requires a WithEvents variable defined in the containing type or one of its base types.

When I remove the MainWindow from the View namespace everything is fine. So clearly the namespace is an issue. Can I add a Window to a namespace and do I need to change something else in the application to make it work?

Answer 1

You are breaking the partial class when you are putting it in a namespace. In addition to moving the VB.NET code behind to the namespace, you need to move the x:Class attribute as well:

<Window x:Class="View.MainWindow" ... />

And

Namespace View
    Class MainWindow
       '...
    End Class
End Namespace

Visual Studio generates a partial VB.NET class that is a partial with your code behind. Since you moved the code behind to another namespace, it is no longer a partial with what Visual Studio generates.