Can muli-inheritance be simulated with generic class in C# [closed]

Question

I have several DataGrid (actually an UserControl based on a DataGrid with filtering dialog, etc.) in a WPF project which show ObservableCollection<VisualXModel> entities where VisualXModel inherits from XModel where X stands for Field, Item, etc. The XModel are in a separate non-UI related library which includes the data access layer. Most of the properties in the XModel are virtual and overriden in the VisualXModel in order to deal with validation.

I also implemented the INotifyPropertyChanged and INotifyDataErrorInfo interfaces, but realise to lead to much duplicated codes.

I wonder if it shouldn't be possible to use a base class VisualModel<XModel> which implements the interfaces as well as other common commands such as CopyCellCommand, EditCommand, RemoveCommand.

But is there a way I can access the generic instance (type parameter) in the "overriden" properties which previously corresponded to the base class? The root part of the inheritance still remain the type parameter.

---

public class XModel
{
    public int Id { get; set; }
    public virtual string Name { get; set; } // Name is made editable from the UI.
}

Currently :

public class VisualXModel : XModel, INotifyPropertyChanged, INotifyDataErrorInfo
{
    public override string Name
    {
        get => base.Name;
        set
        {
            base.Name = value;
            
            // Validation
            // ..
            
            OnPropertyChange(nameof(Name));
        }
    }
    
    // Miscellaneous commands, such as Copy-to-clipboard
    // ..

    // INotifyPropertyChanged, INotifyDataErrorInfo implementations.. which is quite long to duplicate
    // ..
}

With some refactoring

public class VisualModel<T> : INotifyPropertyChanged, INotifyDataErrorInfo
{
    // Miscellaneous commands, such as Copy-to-clipboard
    // ..

    // INotifyPropertyChanged, INotifyDataErrorInfo implementations
    // ..
}

public class VisualXModel : VisualModel<XModel>
{
    public override string Name
    {
        get => How to access / get the Name property of the XModel instance?
        set
        {
            How to access / set the Name property of the XModel instance?

            // Validation
            // ..

            OnPropertyChange(nameof(Name));
        }
    }
}

Answer 1

In my opinion your problem starts that you try to violate Single Responsibility Principle and try to define class that would act as DTO and as view model.

I would take different approach here - separate DTO, which can be even the model class itself and define view model that would implement interfaces INotifyPropertyChanged and INotifyDataErrorInfo.

View model then would take the domain object in it's constructor and "prepare the data" for display.

Roughly the code should look like

public class VisualXModel : INotifyPropertyChanged, INotifyDataErrorInf
{
    public XViewModel(XModel model)
    {
        //...prepare data for display 
    }

    // ... interfaces implementation
}

By the way, by passing XModel through constructor, we are preferring composition over inhertiance here.

Then you have opened options for centralizing code. For instance define common base class for view models:

public class BaseVisual : INotifyPropertyChanged, INotifyDataErrorInf
{
    // ... interfaces implementation
}

// Now view models can be simplified
public class VisualXModel : BaseVisual
{
    public XViewModel(XModel model)
    {
        //...prepare data for display 
    }
}

EDIT You can make use of default interface methods, which would allow you to define IBaseVisual:

public interface IBaseVisual: INotifyPropertyChanged, INotifyDataErrorInf
{
    // ... interfaces implementation with default interface methods
}

public class VisualXModel : XModel, IBaseVisual
{
    // ... you have XModel props and IBaseVisual implementations
}

EDIT Referring to your code sample

public class VisualXModel : VisualModel<XModel>
{
    public override string Name
    {
        get => How to access / get the Name property of the XModel instance?
        set
        {
            How to access / set the Name property of the XModel instance?

            // Validation
            // ..

            OnPropertyChange(nameof(Name));
        }
    }
}

You could put generic parameter contraint. If you have some base class for all models, that for instance defines Name property, then you could write

public class VisualTModel : VisualModel<TModel> where TModel : BaseModel
{
    public override string Name
    {
        get => // Here you will be able to access Name property of TModel object
        set
        {
            // Again you can use object of TModel class as long as it exposes setter property.

            // Validation
            // ..

            OnPropertyChange(nameof(Name));
        }
    }
}