RelayCommand's reference is not found

Question

I have a WPF application in which i'd like to change its design pattern to MVVM.I have used this snippet

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using FirstMVVm.Model;
using System.ComponentModel;
using System.Windows.Input;
using System.Windows;
namespace FirstMVVm.ModelView
{
    class MyViewModel: INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private float result;

          public float Result
          {
           get { return result; }
              private set
              {
                  if (result != value) { 
                      result = value;
                  if (PropertyChanged != null)
                  {
                      PropertyChanged(this, new PropertyChangedEventArgs("Result"));
                  }
                     }
                    }
                 }

          public int Number { get; set; }

        private RelayCommand _calculatePerimeterCommand;

        public ICommand CalculatePerimeterCommand
                  {
                  get
                    {
                    if (_calculatePerimeterCommand == null)
                      {
                          _calculatePerimeterCommand = new RelayCommand(param => this.CalculatePerimeter());
                       }
                    return _calculatePerimeterCommand;
                       }
                      }
        private MyModel _model;

        public MyViewModel() {
            _model = new MyModel();
        }


        private void CalculatePerimeter(){
            Result = _model.Perimetre(Number);
        }

  }
}

The problem is that the RelayCommand type is not known and i don't know what is the assembly missing.

• So how can i fix this problem?

Thanks,

Answer 1

RelayCommand is a class created by MS for handling event or command in WPF. you can create own class or go through below link.

http://msdn.microsoft.com/en-us/magazine/dd419663.aspx

Answer 2

This does not necessarily have to be RelayCommand it's simply a name of class from most common example on the web.

The mechanism of ICommand works in a way that instead of getter or setter being called you get public void Execute(object parameter) to be called on class that is implementing ICommand

Let me give you an example:

I have a hyperlink which when clicked should do some stuff before redirecting person to browser.

XAML

<Hyperlink NavigateUri="https://payments.epdq.co.uk/ncol/prod/backoffice/"
     Command="{Binding Path=NavigateToTakePayment}"  IsEnabled="{Binding CanTakePayment}">
     Launch Payments Portal
</Hyperlink>

now in viewModel I have property

public ICommand NavigateToTakePayment       
{
    get { return _navigateToTakePayment ?? (_navigateToTakePayment = new NavigateToTakePaymentCommand(this)); }
    set { _navigateToTakePayment = value; }
}

but when hyperlink is clicked instead of getter being fired like one would expect NavigateToTakePaymentCommand class Execute method is fired instead.

  public class NavigateToTakePaymentCommand : ICommand
  {
        public NavigateToTakePaymentCommand(PaymentViewModel paymentViewModel)
        {
            ViewModel = paymentViewModel;
        }

        public PaymentViewModel ViewModel { get; set; }

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

        public void Execute(object parameter)
        {
         //your implementation stuff goes here.
        }

        public event EventHandler CanExecuteChanged;
  }

I hope this example will clarify how the mechanism works and will save you some time.