How to remove event handler

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  • moondaddy
    #1

    How to remove event handler

    I'm working in WPF and c# and am adding an event handler to an object like
    this:



    this.tgt.SizeCh anged += new SizeChangedEven tHandler(OnTarg etSizeChanged);



    Later I kill the instance of tgt like this:

    tgt = null;; //which I'm not sure this is the most correct way of getting
    rid of it.



    However, I find that the event 'OnTargetSizeCh anged' is still fireing.
    Evedently the event handler is still alive and wired. Before I kill the
    object 'tgt', should I be removing any attached event handlers? If so, how?



    Thanks.





    moondaddy@noema il.noemail


    Tags: None
    • Jon Skeet [C# MVP]
      #2
      Re: How to remove event handler

      moondaddy <moondaddy@noem ail.noemailwrot e:
      I'm working in WPF and c# and am adding an event handler to an object like
      this:
      >
      this.tgt.SizeCh anged += new SizeChangedEven tHandler(OnTarg etSizeChanged);
      >
      Later I kill the instance of tgt like this:
      >
      tgt = null;; //which I'm not sure this is the most correct way of getting
      rid of it.
      That's not "killing" anything. It's making the object available to the
      garbage collector *if* nothing else is referencing it. Is it still a
      control on the form, perhaps?
      However, I find that the event 'OnTargetSizeCh anged' is still fireing.
      Evedently the event handler is still alive and wired. Before I kill the
      object 'tgt', should I be removing any attached event handlers? If
      so, how?
      Well, I think you need to seriously consider how you're "removing" tgt,
      but to remove the event handler, just do:

      this.tgt.SizeCh anged -= new SizeChangedEven tHandler
      (OnTargetSizeCh anged);


      --
      Jon Skeet - <skeet@pobox.co m>
      http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
      If replying to the group, please do not mail me too

        Comment

        • Keith Patrick
          #3
          Re: How to remove event handler

          Wouldn't that fail due to the SizeChangedEven tHandler being a different
          instance than was added via +=?



            Comment

            • Jon Skeet [C# MVP]
              #4
              Re: How to remove event handler

              Keith Patrick <richard_keith_ patrick@nospam. hotmail.comwrot e:
              Wouldn't that fail due to the SizeChangedEven tHandler being a different
              instance than was added via +=?
              No. They'd still compare as being equal, which is what's used.

              --
              Jon Skeet - <skeet@pobox.co m>
              http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
              If replying to the group, please do not mail me too

                Comment

                • Keith Patrick
                  #5
                  Re: How to remove event handler

                  Well, cool! I was gonna do the -= on some code a while back but saw the new
                  instance I had to create and didn't even check to see if it would work.
                  Guess I can finally fix that!



                    Comment

                    • moondaddy
                      #6
                      Re: How to remove event handler

                      Thanks this looks like just what I need. By the way, this code is running
                      in a class that manages some custom bindings and tgt is a reference to a
                      user control on a canvas. when I connect a line to tgt, I use a custom
                      binding in this class. When tgt becomes un-connected I unbind it from the
                      line and no longer need a reference to tgt so I set tgt=null in the binding
                      management class. However, tgt is still alive and well in the canvas.
                      Saying all of this, is it appropriate to set tgt to null here? or should I
                      do something else?


                      "Jon Skeet [C# MVP]" <skeet@pobox.co mwrote in message
                      news:MPG.204eaa b454353bec98d8e 3@msnews.micros oft.com...
                      moondaddy <moondaddy@noem ail.noemailwrot e:
                      >I'm working in WPF and c# and am adding an event handler to an object
                      >like
                      >this:
                      >>
                      >this.tgt.SizeC hanged += new SizeChangedEven tHandler(OnTarg etSizeChanged);
                      >>
                      >Later I kill the instance of tgt like this:
                      >>
                      >tgt = null;; //which I'm not sure this is the most correct way of
                      >getting
                      >rid of it.
                      >
                      That's not "killing" anything. It's making the object available to the
                      garbage collector *if* nothing else is referencing it. Is it still a
                      control on the form, perhaps?
                      >
                      >However, I find that the event 'OnTargetSizeCh anged' is still fireing.
                      >Evedently the event handler is still alive and wired. Before I kill the
                      >object 'tgt', should I be removing any attached event handlers? If
                      >so, how?
                      >
                      Well, I think you need to seriously consider how you're "removing" tgt,
                      but to remove the event handler, just do:
                      >
                      this.tgt.SizeCh anged -= new SizeChangedEven tHandler
                      (OnTargetSizeCh anged);
                      >
                      >
                      --
                      Jon Skeet - <skeet@pobox.co m>
                      http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
                      If replying to the group, please do not mail me too

                        Comment

                        • Jon Skeet [C# MVP]
                          #7
                          Re: How to remove event handler

                          moondaddy <moondaddy@noem ail.noemailwrot e:
                          Thanks this looks like just what I need. By the way, this code is running
                          in a class that manages some custom bindings and tgt is a reference to a
                          user control on a canvas. when I connect a line to tgt, I use a custom
                          binding in this class. When tgt becomes un-connected I unbind it from the
                          line and no longer need a reference to tgt so I set tgt=null in the binding
                          management class. However, tgt is still alive and well in the canvas.
                          Saying all of this, is it appropriate to set tgt to null here? or should I
                          do something else?
                          If you want the user control to actually "die" you'll need to remove it
                          from the canvas too. If you just want to not reference it any more from
                          tgt, then setting tgt to null is entirely appropriate.

                          --
                          Jon Skeet - <skeet@pobox.co m>
                          http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
                          If replying to the group, please do not mail me too

                            Comment

                            • moondaddy
                              #8
                              Re: How to remove event handler

                              Great! Thanks alot.


                              "Jon Skeet [C# MVP]" <skeet@pobox.co mwrote in message
                              news:MPG.204f40 06e7c92e1b98d8e 8@msnews.micros oft.com...
                              moondaddy <moondaddy@noem ail.noemailwrot e:
                              >Thanks this looks like just what I need. By the way, this code is
                              >running
                              >in a class that manages some custom bindings and tgt is a reference to a
                              >user control on a canvas. when I connect a line to tgt, I use a custom
                              >binding in this class. When tgt becomes un-connected I unbind it from
                              >the
                              >line and no longer need a reference to tgt so I set tgt=null in the
                              >binding
                              >management class. However, tgt is still alive and well in the canvas.
                              >Saying all of this, is it appropriate to set tgt to null here? or should
                              >I
                              >do something else?
                              >
                              If you want the user control to actually "die" you'll need to remove it
                              from the canvas too. If you just want to not reference it any more from
                              tgt, then setting tgt to null is entirely appropriate.
                              >
                              --
                              Jon Skeet - <skeet@pobox.co m>
                              http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
                              If replying to the group, please do not mail me too

                                Comment

                                • moondaddy
                                  #9
                                  Re: How to remove event handler


                                  "Jon Skeet [C# MVP]" <skeet@pobox.co mwrote in message
                                  news:MPG.204f40 06e7c92e1b98d8e 8@msnews.micros oft.com...
                                  moondaddy <moondaddy@noem ail.noemailwrot e:
                                  >Thanks this looks like just what I need. By the way, this code is
                                  >running
                                  >in a class that manages some custom bindings and tgt is a reference to a
                                  >user control on a canvas. when I connect a line to tgt, I use a custom
                                  >binding in this class. When tgt becomes un-connected I unbind it from
                                  >the
                                  >line and no longer need a reference to tgt so I set tgt=null in the
                                  >binding
                                  >management class. However, tgt is still alive and well in the canvas.
                                  >Saying all of this, is it appropriate to set tgt to null here? or should
                                  >I
                                  >do something else?
                                  >
                                  If you want the user control to actually "die" you'll need to remove it
                                  from the canvas too. If you just want to not reference it any more from
                                  tgt, then setting tgt to null is entirely appropriate.
                                  >
                                  --
                                  Jon Skeet - <skeet@pobox.co m>
                                  http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
                                  If replying to the group, please do not mail me too

                                    Comment

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