C# Delegation is not being removed

Question

In the program I have multiple panels being created with picture boxes. The picture boxes are delegated to be clickable. I would like to have the user to have the option to remove one of the panels/picture boxes from the order. Right now if it is removed and the order is rearranged all picture boxes after the one that was removed retains its delegated order. So clicking on any of them after the one that was removed, skips to the one next to it down the line (ie click on #9 and it will go to #10). I need to remove the delegation of the reordered ones and re delegate them correctly. I have tried:

int z2 = z;
var myClickDelegate = (EventHandler)delegate { clicked(z2, null); };
PicBx[z].Click += myClickDelegate;

to create and

PicBx[z].Click -= myClickDelegate;

to remove

and also

int z2 = z;
PicBx[z].Click -= delegate { clicked(z2, null); };

but both of them does not remove the origional delegation.

Answer 1

Your first method should work, but the later one shouldn't work.
because when you do PicBx[z].Click -= delegate { clicked(z2, null); }; method you are not removing the old delegate, instead you are creating a new delegate and then removing it.

In your first try this should work:

private void SomeMethod()
{
    var myClickDelegate = (EventHandler)delegate { clicked(z2, null); };
    PicBx[z].Click += myClickDelegat;
    //Do extra work
    PicBx[z].Click -= mayClickDelegat;
}

Edit: Pair to your comment: I notice that you are only in your delegate adding clicked(z2, null), so I assumed that you are only creating the delegate at the first place just to pass that int z2 to represent the picture box index.
You can put that index with the picture box itself by using pictureBox.Tag and in the click event get that int from the tag:

int z2 = z;
picBx[z].Tag = z2;//here we embedded the number with the picture box.
PicBx[z].Click += clicked;
...
PicBx[z].Click -= clicked;

And so in the clicked event:

private void clicked(object sender, EventArgs e)
{
    PictureBox pictureBox = sender as PictureBox;

    if (pictureBox != null)
    {
        int number = Convert.ToInt32(pictureBox.Tag);
        ...
    }
}

Edit2: As pair to your comments, it seems like you have a different signature of the clicked method:

private void clicked(int tes,..
{
    Pnl[tes].BackColor = Color.Red;
}

Here we only change it to be:

private void clicked(object sender, EventArgs e)
{
    PictureBox pictureBox = sender as PictureBox;//when user clicks on picture box it will be the sender parameter.

    if (pictureBox != null)
    {
        //we add number to each of picture boxes at there tags. "picBx[z].Tag = z2"
        int tes = Convert.ToInt32(pictureBox.Tag);
        pnl[tes].BackColor = Color.Red;
    }
}

Answer 2

You are not trying to delete the same delegate. You should try to store your delegates somewhere:

this.MyDelegate = delegate { clicked(z2, null); };

PicBx[z].Click += this.MyDelegate;


...

...


PicBx[z].Click -= this.MyDelegate;

But playing with delegates like that could lead to bad design choice. You should define a bool in which you'd determine if you execute your delegate or not.

public void OnClick(object sender, ...)
{
    if(myBool)
    {
        ...
    }
}

Answer 3

From your comment to Jalal answer, looks like you may actually need something like this

How to remove all event handlers from a control

Answer 4

You have two issues here.

The first is, as others have pointed out, that you need to remove the same instance of the delegate that you added to the event handler.

The second is that you are using an array to store your picture boxes and your handlers are using an index to look up your picture box so when you remove a picture box from the array all of the event handlers for picture boxes higher in the array would be pointing at the wrong picture box.

Here's what to do:

Step 1: Change your event handler to take an instance of the picture box and not the index to the array.

Step 2: Create a class-level dictionary to hold your delegate references by picture box:

Dictionary<PictureBox, EventHandler> _pictureBoxHandlers =
    new Dictionary<PictureBox, EventHandler>();

Step 3: Write your subscribe code like this:

//After the picture box is added to `PicBx`
var pb = PicBx[z];
var myClickDelegate = (EventHandler)delegate { clicked(pb, null); };
_pictureBoxHandlers[pb] = myClickDelegate;
pb.Click += myClickDelegate;

Step 4: Write your unsubscribe code like this:

//Before the picture box is removed from `PicBx`
var pb = PicBx[z];
if (_pictureBoxHandlers.ContainsKey(pb))
{
    var myClickDelegate = _pictureBoxHandlers[pb];
    pb.Click -= myClickDelegate;
    _pictureBoxHandlers.Remove(pb);
}

See how that goes.