Windows Universal App UI Library Parser internal error

Question

I built a user control in an user control library and I want to include it into my windows universal app. I remember in the old days you had to add something to app.xaml (something like pack:// this is my xaml).

So my thoughts (or hope) I just include my library and user the control. When I do I get - Parser internal error: Object writer 'xClassNotDerivedFromElement'.

I tried adding it as a msappx reference in the App.Xaml, but I may have the syntax wrong. If I can get this working by literally copying over the code itself into my project (which I do not want to do). Suggestions? Thanks

EDIT: Added source code

public MainPage()
{
    _webControl = new NativeWebView.WebUserControl();
    _webControl.Loaded += _webControl_Loaded;
    _contentView = new NativeWebView.ContentView(_webControl);
    this.InitializeComponent();
    root.Children.Add(_webControl);
}


public sealed partial class WebUserControl : UserControl, IWebView
{
    public WebUserControl()
    {
        this.InitializeComponent();
    }

}

Answer 1

So, I found out the answer. So to include a library into another project, you have to have some extra crazy files (.xr.xml and .xrc). I manually copied them into a folder, but it seems they can get out of date. I found that if I want to include the library from the build directory, I have to check a box in the build properties page (Generate library layout). This copies the files for me. SOLUTION!

Answer 2

Just add namespace of the library into root tag of the page where you use the control, ex. for ImageButton control in WinRT XAML Toolkit:

<Page
[...]
xmlns:toolkit="using:WinRTXamlToolkit.Controls">

[...]

<toolkit:ImageButton [...] />

[...]

If you still get xClassNotDerivedFromElement, it means there's a problem in the library. (need source to track it)