ICommand MVVM implementation

Question

So in this particular MVVM implementation I m doing  I need several commands  I really got tired of implementing the ICommand classes one by one  so I came up with a solution  but I don t know how good it is  so the input of any WPF expert here will be greatly appreciated  And if you could provide a better solution  even better   What I did is a single ICommand class and two delegates which take an object as a parameter  one delegate is void  for OnExecute   the other bool  for OnCanExecute   So in the constructor of my ICommand  which is called by the ViewModel class  I send the two methods  and on each ICommand method I invoke the delegates  methods   It works really good  but I m not sure if this is a bad way to do it  or if there s a better way  Below is the complete code  any input will be greatly appreciated  even negative  but please be constructive   ViewModel   public class TestViewModel   DependencyObject       public ICommand Command1   get  set        public ICommand Command2   get  set        public ICommand Command3   get  set         public TestViewModel                 this Command1   new TestCommand ExecuteCommand1  CanExecuteCommand1           this Command2   new TestCommand ExecuteCommand2  CanExecuteCommand2           this Command3   new TestCommand ExecuteCommand3  CanExecuteCommand3              public bool CanExecuteCommand1 object parameter                return true             public void ExecuteCommand1 object parameter                MessageBox Show  Executing command 1               public bool CanExecuteCommand2 object parameter                return true             public void ExecuteCommand2 object parameter                MessageBox Show  Executing command 2               public bool CanExecuteCommand3 object parameter                return true             public void ExecuteCommand3 object parameter                MessageBox Show  Executing command 3              ICommand   public class TestCommand   ICommand       public delegate void ICommandOnExecute object parameter       public delegate bool ICommandOnCanExecute object parameter        private ICommandOnExecute  execute      private ICommandOnCanExecute  canExecute       public TestCommand ICommandOnExecute onExecuteMethod  ICommandOnCanExecute onCanExecuteMethod                 execute   onExecuteMethod           canExecute   onCanExecuteMethod              region ICommand Members      public event EventHandler CanExecuteChanged               add   CommandManager RequerySuggested    value            remove   CommandManager RequerySuggested -  value               public bool CanExecute object parameter                return  canExecute Invoke parameter              public void Execute object parameter                 execute Invoke parameter               endregion

User · Accepted Answer

This is almost identical to how Karl Shifflet demonstrated a RelayCommand, where Execute fires a predetermined Action<T>. A top-notch solution, if you ask me.

public class RelayCommand : ICommand
{
    private readonly Predicate<object> _canExecute;
    private readonly Action<object> _execute;

    public RelayCommand(Predicate<object> canExecute, Action<object> execute)
    {
        _canExecute = canExecute;
        _execute = execute;
    }

    public event EventHandler CanExecuteChanged
    {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute(parameter);
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }
}

This could then be used as...

public class MyViewModel
{
    private ICommand _doSomething;
    public ICommand DoSomethingCommand
    {
        get
        {
            if (_doSomething == null)
            {
                _doSomething = new RelayCommand(
                    p => this.CanDoSomething,
                    p => this.DoSomeImportantMethod());
            }
            return _doSomething;
        }
    }
}

Read more:
Josh Smith (introducer of RelayCommand): Patterns - WPF Apps With The MVVM Design Pattern

User · Answer

Carlo I really like your implementation of this  but I wanted to share my version and how to use it in my ViewModel  First implement ICommand  public class Command   ICommand       public delegate void ICommandOnExecute        public delegate bool ICommandOnCanExecute         private ICommandOnExecute  execute      private ICommandOnCanExecute  canExecute       public Command ICommandOnExecute onExecuteMethod  ICommandOnCanExecute onCanExecuteMethod   null                 execute   onExecuteMethod           canExecute   onCanExecuteMethod              region ICommand Members      public event EventHandler CanExecuteChanged               add   CommandManager RequerySuggested    value            remove   CommandManager RequerySuggested -  value               public bool CanExecute object parameter                return  canExecute  Invoke      true             public void Execute object parameter                 execute  Invoke                endregion     Notice I have removed the parameter from ICommandOnExecute and ICommandOnCanExecute and added a null to the constructor   Then to use in the ViewModel  public Command CommandToRun WithCheck       get               return new Command      gt                           Code to run                 gt                           Code to check to see if we can run                 Return true or false                      public Command CommandToRun NoCheck       get               return new Command      gt                           Code to run                       I just find this way cleaner as I don t need to assign variables and then instantiate  it all done in one go

User · Answer

I ve just created a little example showing how to implement commands in convention over configuration style  However it requires Reflection Emit   to be available  The supporting code may seem a little weird but once written it can be used many times  Teaser  public class SampleViewModel  BaseViewModelStub       public string Name   get  set          UiCommand      public void HelloWorld                 MessageBox Show  quot Hello World  quot                UiCommand      public void Print                 MessageBox Show String Concat  quot Hello   quot   Name   quot   quot     quot SampleViewModel quot               public bool CanPrint                 return  String IsNullOrEmpty Name              UPDATE  now there seem to exist some libraries like http   www codeproject com Articles 101881 Executing-Command-Logic-in-a-View-Model that solve the problem of ICommand boilerplate code

User · Answer

I have written this article about the ICommand interface    The idea - creating a universal command that takes two delegates  one is called when ICommand Execute  object param  is invoked  the second checks the status of whether you can execute the command  ICommand CanExecute  object param     Requires the method to switching event CanExecuteChanged  It is called from the user interface elements for switching the state CanExecute   command   public class ModelCommand   ICommand        region Constructors      public ModelCommand Action lt object gt  execute            this execute  null           public ModelCommand Action lt object gt  execute  Predicate lt object gt  canExecute                 execute   execute           canExecute   canExecute              endregion       region ICommand Members      public event EventHandler CanExecuteChanged       public bool CanExecute object parameter                return  canExecute    null    canExecute parameter    true             public void Execute object parameter                if   execute    null               execute parameter              public void OnCanExecuteChanged                 CanExecuteChanged this  EventArgs Empty               endregion      private readonly Action lt object gt   execute   null      private readonly Predicate lt object gt   canExecute   null

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