Unloadable Plugin Architecture in .NET

[A Popat]

This is my first question here, so apologies if I have made a mistake.

I am developing a collection of small games using WPF with C# but have been having real difficulty in being able to load and unload each game into my main viewer application.

The structure of my program is I have a main view application GameViewer.EXE which basically consists of a Frame object to view pages.
Each game is a custom class GamePage.CS, shown below:

GameLibrary.DLL

namespace GameLibrary
{
 public class GamePage : Page
    {
        public Guid GameID;
        public string GameName;
        public string Description;
        public virtual void PauseGame(){}

       public event GameEndArgsEventHandler GameEnd;

        protected void OnGameEnd(GameEndArgs e)
        {
            if (GameEnd != null)
                GameEnd(this, e);
        }
   }

 public class GameEndArgs : EventArgs
    {
        public double Score;
        public bool Finished;
        public int Level = 1;
    }
}

I also have a ControlLibrary. DLL , which contains a collection of stylized controls, i.e. customs, sliders, etc., which is used in all games and the main interface GameViewer.EXE.

The structure of the application is:

Home\
         GameViewer.EXE
         GameLibrary.DLL
         ControlLibrary.DLL
 
        Games\
                  Game1\
                             game1.DLL
                             game1Dependency1.DLL
                             game1Dependency2.DLL
                  Game2\
                            game2.DLL
                  Game3\
                            game3.DLL
                            image\
                     ...
                 Game n

My trouble is being able to load then successfully unload each game DLL into my main viewer. I have been reading dozen of threads, but I cannot seem to get anything to work. I am trying to create a new AppDomain load the assembly in there and create the GamePage object.
- I can then unload the appdomain when the game is finished, but on repeated opening and closing the game I see the memory usuage shoot up, so something is going wrong.
- I have also tried creating a separate loader, using the MarshalByRefObj ect, but on returning a GamePage I am told that GamePage is not Serializable.

This is my current attempt:

In the GameLibrary.DLL I have:

namespace GameLibrary
{
     [Serializable]
      public class Factory
      {
          public GamePage CreateGamePageObject(string path, string typename)
          {
              return Activator.CreateInstanceFrom(path, typename).Unwrap() as GamePage;
           }
      }
}

Then in the my app I have:

        private AppDomain domain  =null;

         void LoadGame(string GameFile)
          {
                domain = AppDomain.CreateDomain("Remote Load");

                ObjectHandle oh = domain.CreateInstance("GameLibrary", "GameLibrary.Factory");
                Object obj = oh.Unwrap();
                GameLibrary.Factory f = obj as GameLibrary.Factory;
                GameLibrary.GamePage addIn=null;

                FileInfo fi = new FileInfo(GameFile);
               addIn =f.CreateGamePageObject(fi.FullName, fi.Name.Substring(0, fi.Name.Length - 4) + ".Page1");

                MainFrame.Content = addIn;
          }
         void UnloadGame()
         {
               MainFrame.Content = null;
               AppDomain.Unload(domain);
         }

The trouble with this is the memory leak.

I would greatly appreciate any help and suggestions.

[A Popat]

I have since realised that the reason for the increasing memory usage was due to the use of a Frame, which would store a history of past pages. By setting Frame.JournalOw nership to UsesParentJourn al, this problem is avoided.