VisualStudio confuses Avalonia XAML files with WPF XAML

Update: Workaround - use .axaml file extension instead of .xaml.

---

I created a custom Window this way:

namespace MyProject.Desktop.Views
{
    public abstract class BaseWindow : Window
    {
        public BaseWindow()
        {
            this.InitializeComponent();
#if DEBUG
            this.AttachDevTools();
#endif
        }

        protected void InitializeComponent()
        {
            AvaloniaXamlLoader.Load(this);
        }

        [...]
    }
}

Now I use it in my views:

(MainWindow.xaml)

<base:BaseWindow 
        xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:base="clr-namespace:MyProject.Desktop.Views"
        mc:Ignorable="d"
        x:Class="MyProject.Desktop.Views.Main.MainWindow"
        Icon="/Assets/icon_square.png"
        Title="MyProject">

    <StackPanel>[...]</StackPanel>
</base:BaseWindow>

In MainWindow.xaml.cs, the view is declared as

namespace SparkEvo.Desktop.Views.Main
{ 
    public partial class MainWindow : BaseWindow
    [...]

At this point, the XAML designer in Visual Studio 2017 gets full of errors…

It does not recognize the tags anymore (“The type XXXX was not found. Verify that you are not missing an assembly reference.”). But…

• If I make MainWindow a simple Window, so that it does not extend BaseWindow, the error disappears.
• I can compile even with this error, but the XAML designer is unusable, example there is no autocomplete and working gets really difficult.

Avalonia version: 0.8.0 Target Frameworks: netcoreapp2.2;net461

[grokys]

#111 contains a workaround for this issue. It doesn’t fix the underlying issue but at least allows you to open a XAML file with the Avalonia editor from the “Open With…” menu. Thanks @donandren for coming up with this.

[grokys]

@stevenbrix yeah, the problem is this:

Visual Studio works on the xmlns of the root element, not the root xmlns declaration. Because BaseWindow is not in the https://github.com/avaloniaui namespace, it gives up and shows the WPF designer 😦

So it’s showing the WPF designer instead of ours because base:BaseWindow is in the clr-namespace:MyProject.Desktop.Views and not in the avalonia namespace.

IMO it should be looking at the xmlns="https://github.com/avaloniaui" namespace to decide which designer to show, not the namespace of the root element.

@waliarubal we originally did that, but that caused other problems IIRC (I can’t remember the details right now). Also they’re XAML files, we shouldn’t have to come up with our own extension 😉 This is 100% a bug in VS that should be fixed IMO.