Who's signing the propertyChanged event?

[Alberto]

There's a piece of code taken from the resource. http://howtowpf.ru/mvvm-dlya-chaynikov/

He had a question about the event. PropertyChanged

using System.ComponentModel;
using System.Windows.Input;
namespace firstMVVMapp

{

public class ViewModel : INotifyPropertyChanged

{

//Поля

private int _summa;

//Свойства

public int A { get; set; }

public int B { get; set; }

public int Summa

{

get { return _summa; }

set

{

if (_summa != value)

{

_summa = value;

OnPropertyChanged("Summa");

}

}

}

//Команды

public ICommand ClickCommand { get; set; }

//реализация INotifyPropertyChanged

public event PropertyChangedEventHandler PropertyChanged;

protected virtual void OnPropertyChanged(string propertyName)

{

if (PropertyChanged != null)

{

PropertyChanged(this, new PropertyChangedEventArgs(propertyName));

}

}

//Конструктор

public ViewModel()

{

ClickCommand = new RelayCommand(arg => ClickMethod());

}

//Методы

private void ClickMethod()

{

Summa = A + B;

}

}

}

The question is, in fact, that no one has signed the event. And as far as I'm concerned, it's in method. OnPropertyChanged shall not pass the inspection null♪ But somehow it passes well. There's no signature on the code. += to this event. Why not? null ?

[Cleofas]

Objects are signed. http://msdn.microsoft.com/en-us/library/system.windows.data.binding.aspx when you make the connections. Try to realize this event in a clear way, put a brakepoint in the section. add and look at the glasses:

private event PropertyChangedEventHandler propertyChanged;
private object objectLock = new Object();
public event PropertyChangedEventHandler PropertyChanged

{

add

{

lock (this.objectLock)

{

this.propertyChanged += value;

}

}

remove

{

lock (this.objectLock)

{

this.propertyChanged -= value;

}

}

}