MVP Framework ;)

Presenter.cs

using System.Collections.Generic;

/// <summary>
/// The base class of the Presenter class which does not operate View.
/// </summary>
public abstract class Presenter
{
	protected Presenter()
	{
	}
}

/// <summary>
/// The base class of the Presenter class which operates View
/// </summary>
public abstract class Presenter<TView>
{
	#region properties
	public int ViewsCount
	{
		get
		{
			return views.Count;
		}
	}

	protected List<TView> views;
	#endregion

	#region public methods
	public void AddView(TView view)
	{
		if (view == null || ContainsView(view))
		{
			return;
		}
		views.Add(view);
	}

	public void AddView(TView view, params TView[] moreViews)
	{
		AddView(view);
		AddView(moreViews);
	}

	public void AddView(IEnumerable<TView> views)
	{
		if (views == null)
		{
			return;
		}
		foreach (TView view in views)
		{
			AddView(view);
		}
	}

	public bool ContainsView(TView view)
	{
		return views.Contains(view);
	}

	public void RemoveView(TView view)
	{
		if (view == null || !ContainsView(view))
		{
			return;
		}
		views.Remove(view);
	}

	public void RemoveView(TView view, params TView[] moreViews)
	{
		RemoveView(view);
		RemoveView(moreViews);
	}

	public void RemoveView(IEnumerable<TView> views)
	{
		if (views == null)
		{
			return;
		}
		foreach (TView view in views)
		{
			RemoveView(view);
		}
	}

	public void RemoveAllView(TView view)
	{
		views.Clear();
	}
	#endregion

	#region private methods
	protected Presenter(TView view) : this()
	{
		AddView(view);
	}

	protected Presenter(IEnumerable<TView> views) : this()
	{
		AddView(views);
	}

	protected Presenter()
	{
		views = new List<TView>();
	}

	protected IEnumerable<TView> GetViews()
	{
		return new List<TView>(views);
	}
	#endregion
}

PresenterTest.cs

using NUnit.Framework;
using System.Collections.Generic;

[TestFixture]
public class PresenterTest
{
	public class MockPresenter : Presenter<MockPresenter.IView>
	{
		public interface IView
		{
		}
	}


	public class MockView : MockPresenter.IView
	{
	}

	[Test]
	public void TestViewDuplicationIsNotAllowed()
	{
		MockView view = new MockView();
		MockPresenter presenter = new MockPresenter();
		presenter.AddView(view);
		Assert.AreEqual(1, presenter.ViewsCount);
		Assert.IsTrue(presenter.ContainsView(view));
		presenter.AddView(view);
		Assert.AreEqual(1, presenter.ViewsCount);
		Assert.IsTrue(presenter.ContainsView(view));
	}

	[Test]
	public void TestRangeAddRange()
	{
		int viewsCount = 10;
		List<MockPresenter.IView> views = new List<MockPresenter.IView>();
		for (int i = 0; i < viewsCount; i++)
		{
			views.Add(new MockView());
		}

		MockPresenter presenter = new MockPresenter();

		presenter.AddView(views[0], views[1], views[2], views[3]);
		Assert.AreEqual(4, presenter.ViewsCount);
		Assert.IsTrue(presenter.ContainsView(views[0]));
		Assert.IsTrue(presenter.ContainsView(views[1]));
		Assert.IsTrue(presenter.ContainsView(views[2]));
		Assert.IsTrue(presenter.ContainsView(views[3]));

		presenter.AddView(views);
		Assert.AreEqual(viewsCount, presenter.ViewsCount);
		foreach (MockView view in views)
		{
			Assert.IsTrue(presenter.ContainsView(view));
		}
	}
}