WPF-MVVM: RelayCommand Implementation

In WPF if we are implementing MVVM pattern then we need to play with Command rather than Events. You can use ICommand interface to create each command class. Implementation of ICommand in a class gives you CanExecute(), Execute() methods which take part in the action performed by Command.

 

Rather than making Command Class for each Command we can implement a generic Relay Command to get Command. Below is a RelayCommand class that we will implement.

 

/// <summary>     /// To register commands in MMVM pattern     /// </summary>     class RelayCommands : ICommand     {         readonly Action<object> _execute;         readonly Predicate<object> _canExecute;         /// <summary>         /// Constructer takes Execute events to register in CommandManager.         /// </summary>         /// <param name="execute">Execute method as action.</param>         public RelayCommands(Action<object> execute)             : this(execute, null)         {             try             {                 if (null == execute)                 {                     throw new NotImplementedException("Not implemented");                 }                 _execute = execute;             }             catch (Exception)             {                 throw;             }         }         /// <summary>         /// Constructer takes Execute and CanExcecute events to register in CommandManager.         /// </summary>         /// <param name="execute">Execute method as action.</param>         /// <param name="canExecute">CanExecute method as return bool type.</param>         public RelayCommands(Action<object> execute, Predicate<object> canExecute)         {             try             {                 if (null == execute)                 {                     _execute = null;                     throw new NotImplementedException("Not implemented");                 }                 _execute = execute;                 _canExecute = canExecute;             }             catch (Exception)             {             }         }         /// <summary>         /// Can Executed Changed Event         /// </summary>         public event EventHandler CanExecuteChanged         {             add             {                 CommandManager.RequerySuggested += value;             }             remove             {                 CommandManager.RequerySuggested -= value;             }         }         /// <summary>         /// Execute method.         /// </summary>         /// <param name="parameter">Method parameter.</param>         public void Execute(object parameter)         {             _execute(parameter);         }         /// <summary>         /// CanExecute method.         /// </summary>         /// <param name="parameter">Method parameter.</param>         /// <returns>Return true if can execute.</returns>         public bool CanExecute(object parameter)         {             return _canExecute == null || _canExecute(parameter);         }         /// <summary>         /// InvalidateCanExecute method will initiate validation of the Command.         /// </summary>         private void InvalidateCanExecute()         {             CommandManager.InvalidateRequerySuggested();         }     }

 

 

You need to create object of RelayCommand with delegate as paramenters point to CanExecute and Execute methods.

Like:

 

ICommand _createNewCollegeCommand;        /// <summary>        /// Command to create new College.        /// </summary>        public ICommand CreateNewCollegeCommand        {            get            {                if (_createNewCollegeCommand == null)                {                    _createNewCollegeCommand = new RelayCommands(param => this.CreateNewCollegeCommand_Execute(param),                    param => this.CreateNewCollegeCommand_CanExecute(param));                }                return _createNewCollegeCommand;            }        }        bool CreateNewCollegeCommand_CanExecute(object param)        {            return true;        }        void CreateNewCollegeCommand_Execute(object param)        {            IndividualCollegeViewModel indCollegeVM = this._individualCollegeVMFactory();            //Set the DataContext            (indCollegeVM.View as AddCollege).DataContext = indCollegeVM;            //Show dialog box to add College.            (indCollegeVM.View as AddCollege).Owner = this.CurrentView;            (indCollegeVM.View as AddCollege).ShowDialog();        }

 

Hope this will be helpful to you all.

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