Why is addObserver crashing instantly?

Question

I have various kinds of operations (derived from NSOperation) to do async queries over the Internet. As is the norm, I determine when they're finished by observing their isFinished property.

When one particular type of operation finishes, I want to create a follow-up type of operation using info from the first. But when I do so, calling addObserver on the operation crashes my app with a bad access. Since observers are called in a random thread, I tried creating the follow-up operation and setting the observer on the main thread. No difference. This is being done in observeValueForKeyPath:

GetMessagesOperation* msgOp = 
  [[GetMessagesOperation alloc] initWithUserID:_user.getID()
                                     sinceLast:true
                                 includeSystem:true
                                   includeUser:false
                                      skipRows:0
                                      maxCount:50
                                     DBManager:_pDatabaseMgr];
[msgOp addObserver:self 
        forKeyPath:@"isFinished"
           options:0
           context:getMessageContext];
[_operationQueue addOperation:msgOp];
[msgOp release];

The context is a void* to a string; I use the same syntax for many other operations that work fine. Here's how the contexts are defined:

static void* systemInfoContext = (void*)@"sys";
static void* validateUserContext = (void*)@"user";
static void* getMessageContext = (void*)@"msg";

Anybody have a guess here? Thanks!

Edit: Thanks for the reply. There's no crash log generated. It just quits with a bad access on the addObserver line, and this happens regardless of whether I execute in on the main thread or the background thread in which observeValueForKeyPath is entered.

Answer 1

BAH! The whole problem was a failure to call [super init] in the operation's initialization method.

Thanks to all who answered anyway.