Removing anonymous event handler

Question

I have the following code where SprintServiceClient is a reference to a WCF Service-

public class OnlineService
{
    private SprintServiceClient _client;
           


        

Answer 1

You can refer to your anonymous method from inside itself as long as you assign a delegate to a variable first:

EventHandler<SomeEventArgs> handler = null;
handler = (s, e) =>
    {
        _client.AddMemberToTeamCompleted -= handler;
        callback(e.Result);
    };

_client.AddMemberToTeamCompleted += handler;

Note that you need to declare the variable and assign it separately or the compiler will deem it uninitialized when you come to use it inside the method body.

Answer 2

No there is no way,

Apparantly Tim and Marc have another nice solution

But you can always just name them, and do the -= on the named eventhandler on this method ;)

Guessing your event:

_client.AddMemberToTeamCompleted += OnAddMemberToTeamCompleted;

and

public void OnAddMemberToTeamCompleted(object sender, EventArgs args)
{
    _client.AddMemberToTeamCompleted -= OnAddMemberToTeamCompleted;
    callback(e.Result)
}

Next problem is getting this callback in your listener. Perhaps putting it on a Property in the EventArgs (but that feels kinda dirty, I agree)

Answer 3

The trick to making a self-unsubscribing event-handler is to capture the handler itself so you can use it in a -=. There is a problem of declaration and definite assignment, though; so we can't do something like:

EventHandler handler = (s, e) => {
    callback(e.Result);
    _client.AddMemberToTeamCompleted -= handler; // <===== not yet defined     
};

So instead we initialize to null first, so the declaration is before the usage, and it has a known value (null) before first used:

EventHandler handler = null;
handler = (s, e) => {
    callback(e.Result);
    _client.AddMemberToTeamCompleted -= handler;        
};
_client.AddMemberToTeamCompleted += handler;