VB -> C#: Event handler assignments are placed above InitializeComponent

Repro instructions

1. Create a new VB WPF Application (.NET Framework) project.
2. Fill MainWindow.xaml as follows:

<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="450" Width="800">
    <Button x:Name="btn" />
</Window>

1. Fill MainWindow.xaml.vb as follows:

Class MainWindow
    Private Sub MainWindow_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
        MsgBox("Window loaded")
    End Sub

    Private Sub btn_Click(sender As Object, e As RoutedEventArgs) Handles btn.Click
        MsgBox("Button clicked")
    End Sub
End Class

1. Run the program and note that everythings works as expected: The first message box is shown immediately, and the second one upon clicking the (full-size) button.
2. Convert the project to C# using the Visual Studio Extension.
3. Fix the namespace in the XAML file (depends on your project name, in my case it was x:Class="MainWindow" -> x:Class="WpfApp1.MainWindow").
4. Run the program.

Erroneous output

Neither the window’s nor the button’s event handler gets called, because (a) the XAML file is left unmodified and (b) the Handles clauses from the VB code are gone without replacement. This is what MainWindow.xaml.cs looks like:

using System.Windows;
using Microsoft.VisualBasic;

namespace WpfApp1
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            Interaction.MsgBox("Window loaded");
        }

        private void btn_Click(object sender, RoutedEventArgs e)
        {
            Interaction.MsgBox("Button clicked");
        }
    }
}

Expected output

There are multiple ways to fix this:

Solution 1: Add the event handler names to the XAML file. This would be the most idiomatic solution, but requires parsing and modifying the XAML file, which is probably a lot of work.

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="450" Width="800"
        Loaded="MainWindow_Loaded">
    <Button x:Name="btn" Click="btn_Click" />
</Window>

Solution 2: Add the event handlers in code in the constructor.

        public MainWindow()
        {
            InitializeComponent();

            this.Loaded += MainWindow_Loaded;
            btn.Click += btn_Click;
        }

Solution 3: Inform the user that there is still work that needs to be done:

        // TODO: Attach the event handler to its event. VB version was: "Handles Me.Loaded"
        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            Interaction.MsgBox("Window loaded");
        }

        // TODO: Attach the event handler to its event. VB version was: "Handles btn.Click"
        private void btn_Click(object sender, RoutedEventArgs e)
        {
            Interaction.MsgBox("Button clicked");
        }

Details

• Product in use: VS extension
• Version in use: 9.0.4.0

[GrahamTheCoder]

I’ve found that if people use the WPF designer to add events, they get added in the xaml even in VB, so people will only face this issue if manually adding Handles statements. So yeah if it’s slightly rarer that’s even less reason to dabble with mutating xaml.

It looks like the first part of the reason the event hookups aren’t added is to do with partial classes that WPF generates in the obj folder to represent the xaml. This gets selected as the best place to add the initialization. I’ll see if I can stop that happening. (The files have the .g.i.vb and .g.vb extensions if you’re interested)

[GrahamTheCoder]

Thanks, I’ve reopened this and will try to take another look when I get time