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

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;