Generic method with reflection in factory pattern

Question

I've posted my factory to codereview.so now I've got this:

public class WpfControlFactory
{
    public static TControl CreateWpfControl<TControl>(string name = null) where TControl : class, IWpfControl
    {
        TControl wpfControl = default(TControl);

        //Avoid some bone-headed exceptions
        if (!typeof(TControl).IsAbstract)
        {
            wpfControl = Activator.CreateInstance<TControl>();
        }

        if (wpfControl != null)
        {
            wpfControl.Name = name ?? Consts.DefaultEaControlName;
        }

        return wpfControl;
    }
}

But unfortunately I can't use CreateWpfControl<TControl>() because I don't have TControl I've got only typeName string.

I've read this so I know how to create generic method with reflection. But actually I don't know where should I create it. In factory like this:

    public static IWpfControl CreateWpfControl(string controlType, string controlName)
    {
        Type type = FindType(controlType);
        if (type == null)
        {
            return null;
        }

        MethodInfo method = typeof(WpfControlFactory).GetMethod("CreateInstance");
        MethodInfo generic = method.MakeGenericMethod(type);
        return (IWpfControl)generic.Invoke(null, null);
    }

    private static Type FindType(string typeName)
    {
        Type type = null;
        WpfControl wpfControl;
        Enum.TryParse(typeName, out wpfControl);
        if (wpfControl != default(WpfControl))
        {
            type = Type.GetType(typeName);
        }

        return type;
    }

    private static TControl CreateInstance<TControl>(string name = null) where TControl : class, IWpfControl
    {
        TControl wpfControl = default(TControl);

        //Avoid some bone-headed exceptions
        if (!typeof(TControl).IsAbstract)
        {
            wpfControl = Activator.CreateInstance<TControl>();
        }

        if (wpfControl != null)
        {
            wpfControl.Name = name ?? Consts.DefaultEaControlName;
        }

        return wpfControl;
    }

Or where? I want my class be consistent with SOLID

EDIT

Next possible version:

public class WpfControlFactory
{
    public static IWpfControl CreateWpfControl(string controlType, string controlName = null)
    {
        IWpfControl wpfControl = default(IWpfControl);

        Type type = Type.GetType(controlType);
        if (type != null && type.IsAssignableFrom(typeof(IWpfControl)))
        {
            wpfControl = (IWpfControl)Activator.CreateInstance(type);
        }

        if (wpfControl != null)
        {
            wpfControl.Name = controlName ?? Consts.DefaultEaControlName;
        }

        return wpfControl;
    }
}

Could you say something about the line with `Enum.TryParse`? I can't get the idea. Plus, I don't quite get why you insist on reusing the generic version. Having the type name in hand, you could use the other overload of `CreateInstance` that accepts the type name as string. — Wiktor Zychla, Nov 01 '14 at 10:00
@WiktorZychla I have enum of supported controls, this is important because I'm writing addin to Enterprise Architect and I don't support all controls that it provide. So I check if my controlType is supported type. Edit version in first post. — rechandler, Nov 01 '14 at 10:24

score 0 · Answer 1 · edited Nov 01 '14 at 11:58

Your second approach won't work, you can't get the type out of the controlName. My idea is that if you already have a closed enum, make use of it.

public class WpfControlFactory
{
  public static IWpfControl CreateWpfControl(WpfControl control, string controlName)
  {
    IWpfControl wpfControl = default(IWpfControl);

    Type type = GetControl(control);
    if (type != null && type.IsAssignableFrom(typeof(IWpfControl)))
    {
        wpfControl = (IWpfControl)Activator.CreateInstance(type);
    }

    if (wpfControl != null)
    {
        wpfControl.Name = controlName ?? Consts.DefaultEaControlName;
    }

    return wpfControl;
  }

  private Type GetControl( WpfControl control )
  {
     switch ( control )
     {
        case WpfControl.Foo : return typeof( FooControlType );
        ...
     }
  }
}

This way you have a clean 1-1 mapping between enum values and control types.

On the other hand, if you rely on a string, finding a type is much more difficult. Types can exist in different assemblies. A short type name could just be not enough. And making the caller using a full type name (that also includes the assembly name) would make the invocation more difficult (the caller would have to know the type to get its full name).

At the beginning I also try approach with `swich case` but on [codereview.so](http://codereview.stackexchange.com/questions/68559/factory-pattern-with-controls) wasn't very satisfied. I know about create types limitation, and all my controls I want to create, are in the same assembly with factory. So short type is enough I think. — rechandler, Nov 01 '14 at 11:05

Generic method with reflection in factory pattern

1 Answers1