// Constructor.
        public BattleViewModel()
        {
            Title = "Battle";

            SelectedCharacters  = new ObservableCollection <Character>();
            AvailableCharacters = new ObservableCollection <Character>();
            SelectedMonsters    = new ObservableCollection <Monster>();

            LoadDataCommand = new Command(async() => await ExecuteLoadDataCommand());

            BattleEngine = new BattleEngine();
            BattleEngine.BattleEngineClearData();

            // Load Data
            ExecuteLoadDataCommand().GetAwaiter().GetResult();

            MessagingCenter.Subscribe <OpeningPage, Character>(this, "AddSelectedCharacter", async(obj, data) =>
            {
                SelectedListAdd(data);
            });

            MessagingCenter.Subscribe <OpeningPage, Character>(this, "RemoveSelectedCharacter", async(obj, data) =>
            {
                SelectedListRemove(data);
            });
        }