c# - SimpleIoc.Default.Register fails at IsInDesignModeStatic if the Interface is in different assembly

Question

In the static constructor of ViewModelLocator class the SimpleIoc.Default.Register<T>(); fails at IsInDesignModeStatic mode, if the Interface is in a different project. As a result the MainWindow.xaml designer is empty at design time.

I've made a simple solution to test it. Only changes that I've made is to move the DataItem class and the IDataService interface into the Domain project.

Download here

I've found a walk-around: Add a link to the IDataService.cs in the ClientWpf project.

public class ViewModelLocator {
    static ViewModelLocator() {
        ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);

        if (ViewModelBase.IsInDesignModeStatic) {

            // It fails if the IDataService is in different assembly
            // Delete the link of IDataService.cs from the ViewModel folder...
            SimpleIoc.Default.Register<IDataService, Design.DesignDataService>();
        }
        else {
            SimpleIoc.Default.Register<IDataService, DataService>();
        }

        SimpleIoc.Default.Register<MainViewModel>();
    }
...
}

Answer 1

    if (ViewModelBase.IsInDesignModeStatic) {


        // put these lines here:
        if (SimpleIoc.Default.IsRegistered<IDataService>()) {
            SimpleIoc.Default.Unregister<IDataService>();
        }

        SimpleIoc.Default.Register<IDataService, Design.DesignDataService>();
    }
    else {
        SimpleIoc.Default.Register<IDataService, DataService>();
    }