WPF Custom Routed Events - How to UnSubscribe?

Question

How to DeRegister from one Custom Routed Event.

I have the following code (very standard for Custom Routed Events)

//Dispatch the Video Detection Movements
public delegate void MovementRoutedEventHandler( object sender
                                                , MovementRoutedEventArgs e);
public class MovementRoutedEventArgs : RoutedEventArgs
{
    private readonly DahuaDevice _device;
    private readonly byte[] _canals;
    private readonly DateTime _when;

    public MovementRoutedEventArgs(DahuaDevice device, byte[] canals, DateTime when)
    {
        _device = device;
        _canals = canals;
        _when = when;
    }
    public DahuaDevice Device
    {
        get { return _device; }
    }
    public Byte[] Canals
    {
        get { return _canals; }
    }
    public DateTime When
    {
        get { return _when; }
    }
}
public static RoutedEvent MovementEvent = EventManager.RegisterRoutedEvent(
        "Movement"
    , RoutingStrategy.Tunnel
    , typeof(MovementRoutedEventHandler)
    , typeof(Window)
);

public event RoutedEventHandler Movement
{
    add { AddHandler(MovementEvent, value); }
    remove { RemoveHandler(MovementEvent, value); }
}
public void RaiseMovementEvent(DahuaDevice device, byte[] canals, DateTime when)
{
    RaiseEvent(new MovementRoutedEventArgs(device, canals, when)
    {
        RoutedEvent = MovementEvent
    });
}

Now a class will subscribe to this event with this line:

//Receive the Movement events
EventManager.RegisterClassHandler( 
      typeof(Window)
    , Main.MovementEvent
    , new Main.MovementRoutedEventHandler(MovementHandler));

When I close the class instance, I should UnSubscribe from the event (otherwise, instance won't be garbage collected).

What should I call? I tried RegisterClassHandler(typeof(Window), Main.MovementEvent, **null**) but I get an exception...

Any help welcome. Thanks in advance.

JM

score 10 · Accepted Answer · edited Nov 27 '14 at 05:12

10

You can use RemoveHandler method from System.Windows.Window class (generally from UIElement class).

The code could look something like this:

Main.RemoveHandler( Main.MovementEvent
                  , new Main.MovementRoutedEventHandler(MovementHandler));

edited Nov 27 '14 at 05:12

Noctis

11,507
3
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answered Oct 23 '11 at 21:05

Rafal Spacjer

4,838
2
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Thanks a lot for the quick answer. – Jean-Marie Oct 24 '11 at 00:10
Glad, that I was able to help you. – Rafal Spacjer Oct 24 '11 at 05:33

score 6 · Answer 2 · answered Oct 23 '11 at 20:50

6

I'm not sure if I completely understand what you're doing, but I'll throw in my two cents.

Your EventManager.RegisterClassHandler call should be placed in a static constructor for your class you wish to register. This will apply to all of your instances of the class and should not affect garbage collection.

If you wish to make register/unregister to the event on a per instance level, use the traditional

myEvent += myDelegate;
myEvent -= myDelegate;

Hope this helps.

answered Oct 23 '11 at 20:50

philt5252

939
7
19

Thanks for the answer but can u directly use the + and - when they are "Custom Routed Events"... I am not sure. I will put the RegisterClassHandler in a static constructor to avoid memory leaks. – Jean-Marie Oct 24 '11 at 00:10
Yes you can use the + and - for Custom Routed Events. These are used on an instance level, however since your solution seems to want ALL instances of the class to subscribe to the event, EventManager.RegisterClassHandler is the way to go. However it is also important to note that the method registered to the event should be static or else you will get the memory leak problem you were concerned with. See this [link](http://www.japf.fr/2009/08/wpf-memory-leak-with-eventmanager-registerclasshandler/) – philt5252 Oct 24 '11 at 13:16

WPF Custom Routed Events - How to UnSubscribe?

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