Debugging event subscriptions in C#/.NET

Recently I had to debug a problem around events. I wanted to find out which objects are subscribing to a certain event and when. As there is no code in the class that handles the event subscription, you cannot set a breakpoint there. Too bad...

But there's a simple way out of this. Let's assume you have a class like this:

class Test : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged = delegate { };

    void FirePropertyChanged(string property)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(property));
    }
}

You can add a "custom event implementation" that forwards all event subscriptions and un-subscriptions to a private event, similar to a property that uses a private field to store its value:

class Test : INotifyPropertyChanged
{

    private event PropertyChangedEventHandler propertyChangedImpl = delegate { };
    public event PropertyChangedEventHandler PropertyChanged
    {
        add { this.propertyChangedImpl += value; }
        remove { this.propertyChangedImpl -= value; }
    }

    void FirePropertyChanged(string property)
    {
        this.propertyChangedImpl(this, new PropertyChangedEventArgs(property));
    }
}

The you can simply set the breakpoint to the add method and see exactly where and when these event registrations happen.