Generator for DesignTimeViewModels

[Tommycore]

Hi everyone!

tl;dr: How about a feature that creates a ViewModel parallel to your actual ViewModel which you can use with the d:DataContext attribute?

A common annoyance I encounter is bringing in example data to view in the XAML designer. The way I currently do it is creating 3 files:

• The actual ViewModel class
• An interface defining everything that View and ViewModel interact over
• A DesignTimeViewModel class that implements said interface and delivers example data
  I then bind the DesignTimeViewModel to the window/user control/whatever in the XAML file using d:DataContext="{d:DesignInstance myNamespace:MyDesignTimeViewModel, IsDesignTimeCreatable=True}".

So my ViewModel might have a public int CurrentViews { get; set; } and the DesignTimeViewModel might have a public int CurrentViews { get => 130; set => throw new NotImplementedException(); }. As you can imagine, this is quite tedious to work with, so my idea would be to use specific attributes and source generators to automatically create those DesignTimeViewModels.

For example:

public class BottleViewModel
{
    [CreateDesignTimeData("Random", 10, 100)]
    public int Price { get; set; }

    [CreateDesignTimeData]
    public DrinkCategory Category { get; }

    [CreateDesignTimeData("ProductName")]
    public string Name { get; set; }
}

should create

public class BottleDesignTimeViewModel
{
    public int Price { get => Random.Shared.Next(10, 100); set => throw new NotImplementedException(); } 
    public DrinkCategory Category { get => EnumHelper.GetRandomValue<DrinkCategory>(); }
    public string Name { get => NamingHelper.GetRandomProductName(); set => throw new NotImplementedException(); } 
}

This is a rough idea at an early stage, so I'd love to hear some feedback. Do you think the Toolkit would benefit from this or should I rather go ahead and create my own project? Should it be implemented in a way that those attributes can be used alongside existing [ObservableProperty] generators or would that cause trouble? Any pitfalls you foresee? What datasources to use? I mean, generating a random number between X and Y is easy, but pulling a random name from a list requires said list in the first place.

Thanks for your thoughts and insights,
Tommycore