How can i set a control event to null

Question

H,

I have a listView with an event set to ItemChecked, now i need to do something like:

var tmp = this.listView.ItemChecked;
this.listView.ItemChecked = null; //set the event to null

// run some code which checkes some item in the list
// wehre the event shouldnt get fired on

this.listView.ItemChecked = tmp; //set the event again

Problem is that i can not read the event, i get the message that it can be used only on the left side of a statement.

Any Ideas?

Can't you just unsubscribe all handlers, cache them in a local list, then re-subscribe them afterwards? — Chris, Nov 13 '12 at 13:40
Check out the following answer [How to remove all event handlers from a control](http://stackoverflow.com/a/5475424/519383). — juan.facorro, Nov 13 '12 at 13:44
@juan.facorro that only works if it's *your* event. See the accepted answer on that question. — Jon B, Nov 13 '12 at 13:47

score 1 · Accepted Answer · answered Nov 13 '12 at 13:41

1

this.listView.ItemChecked -= myEventHandler;

// run some code

this.listView.ItemChecked += myEventHandler;

answered Nov 13 '12 at 13:41

Cole Cameron

2,213
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score 1 · Answer 2 · answered Nov 13 '12 at 13:41

1

You can unsubscribe and resubscribe to do what you're trying to do:

private void listView1_ItemChecked(object sender, ItemCheckedEventArgs e)
{
    listView1.ItemChecked -= new ItemCheckedEventHandler(listView1_ItemChecked);

    // do stuff

    listView1.ItemChecked += new ItemCheckedEventHandler(listView1_ItemChecked);
}

answered Nov 13 '12 at 13:41

Jon B

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What if the code is not able to assume that `listView1_ItemChecked` is the only subscribed handler? – David Heffernan Nov 13 '12 at 13:43
@DavidHeffernan that gets a lot harder: http://stackoverflow.com/questions/91778/how-to-remove-all-event-handlers-from-a-control – Jon B Nov 13 '12 at 13:46
But that's what the question is about. – David Heffernan Nov 13 '12 at 13:47

score 1 · Answer 3 · answered Nov 13 '12 at 13:53

You could remove then add the event handler. Assuming your code is in a method named ItemChecked

listView.ItemChecked -= ItemChecked;

// do whatever

listView.ItemChecked += ItemChecked;

However, I prefer checking for re-entrant calls.

object alreadyInItemChecked;

void ItemChecked(object s, EventArgs e)
{
   if (Monitor.TryEnter(alreadyInItemChecked))
   {
      try
      {
          // do whatever
      }
      finally
      {
          Monitor.Exit(alreadyInItemChecked)
      }
   }
 }

score 0 · Answer 4 · answered Nov 13 '12 at 13:44

You can subscribe / unsubscribe to events as something like this.

        this.someObject.someObjectEvent += someEventHandler;
        this.someObject.someObjectEvent -= null;

So subscribe when you want the event to be fired and unsubscribe when not needed.

How can i set a control event to null

4 Answers4