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POWhy is addObserver crashing instantly?
 

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  1. POWhy is addObserver crashing instantly?
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    <p>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.</p> <p>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:</p> <pre><code>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]; </code></pre> <p>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:</p> <pre><code>static void* systemInfoContext = (void*)@"sys"; static void* validateUserContext = (void*)@"user"; static void* getMessageContext = (void*)@"msg"; </code></pre> <p>Anybody have a guess here? Thanks!</p> <p>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.</p>
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    1. USOscar
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    1. COcan you attach crash logs and code instance where it crashes.
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      1. USrishi
    2. COI am not sure what you did or how other code is but try this [msgOp addObserver:self forKeyPath:@"isFinished" options:0 context:&getMessageContext];
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      1. USIducool
    3. COwild guess: you are observing a property of an object which is released by the queue (and therefore deallocated) as soon as this property changes. The object (and therefore the property) does not exist at the instant it is changed. This may leave memory management in a degenerate state, leading to unexpected crashes. As a quick test: what would happen if you leave out the `[msgOp release]` call here?
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      1. USmvds
 

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