Disposal of event handlers
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Thread: Disposal of event handlers

  1. #1
    Join Date
    Nov 2009
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    Disposal of event handlers

    When I use the designer to generate Event Handlers for my Click events it adds a line of code which adds a delegate instance to the event eg

    this.button1 = new System.Windows.Forms.Button();
    this.button1.Click += System.EventHandler (this.button1_Click);

    However, the designer does not provide the code which removes the event handler from the Click event.

    Does this mean that when I add my own event handlers, using the += syntax, I also do not have to remove them using the -= syntax? Or will this cause memory leaks?

    Thanks in advance

  2. #2
    Join Date
    Mar 2004
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    Prague, Czech Republic, EU
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    1,701

    Re: Disposal of event handlers

    Simply: it depends. Event handlers generated by the designer is local to the form, so if the instance of the is GC'ed out, they cannot be more executed. Also, it is supposed that no more events can occure on closed form, because form's events are related to GUI. If you attach your own handler, especially on you own event, it is upon you to ensure that is (not) called properly. If the target method of the event handler (keep in mind it is a delegate) belongs to other instance, it can cause memory leaks if it is not properly detached.
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  3. #3
    Join Date
    Oct 2003
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    .NET2.0 / VS2005 Developer
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    7,104

    Re: Disposal of event handlers

    Quote Originally Posted by Rachel888s View Post
    However, the designer does not provide the code which removes the event handler from the Click event.
    Indeed, it is a reasonable expectation that you wouldnt want to unlink an event handler you have linked at design time

    Does this mean that when I add my own event handlers, using the += syntax, I also do not have to remove them using the -= syntax? Or will this cause memory leaks?
    As Bou says, it depends on how long you expect your object raising the event, to last. It is reasonable to expect that the form will last the life of the app and so its event handler will be linked all that time.. If you tell us more about the life of the object that raises events and why sometimes you might not want to listen to them, we can tell you if you need to remove the handlers or not
    "it's a fax from your dog, Mr Dansworth. It looks like your cat" - Gary Larson...DW1: Data Walkthroughs 1.1...DW2: Data Walkthroughs 2.0...DDS: The DataSet Designer Surface...ANO: ADO.NET2 Orientation...DAN: Deeper ADO.NET...DNU...PQ

  4. #4
    Join Date
    Nov 2009
    Posts
    4

    Re: Disposal of event handlers

    The object will be raising the event for the lifetime of my Tab Control which is displayed on a Tab Page. I have now implemented a method which is called on closing the property page that unregisters the event handler.

    Thanks for your help.

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