Timing of delegate method invocation!!

Question

In my app, I use MKReverseGeocoder method to to build (location) string that some other class uses it as output to the user. In testing I see that very often the location string is not displayed. I kept thinking that the MKReverseGecoder is failing - but it is not. It is a timing issue.
What I do is that I build the (location) string (e.g. Las Vegas, Nevada, US) in the delegate method for MKReverseGeocoder. That string is stored in one of the the AppDelegate's instance variables. The consumer of the location string then accesses it later on.
In the following snapshot of the console log, the delegate method logs (-----> Las Vegas, Nevada, US) and the consumer logs (===> string value). The first section shows that the delegate is called after the consumer is called - that's why the value is "not set yet". The second section shows the intended sequence of execution.
2010-05-31 17:28:21.517 Sam[6677:207] delegateEmailSetup=YES // Try 1.
2010-05-31 17:28:43.489 Sam[6677:207] Location manager initialized
2010-05-31 17:28:44.023 Sam[6677:207] geocoder = (null)
2010-05-31 17:28:44.073 Sam[6677:207] geocoder = <MKReverseGeocoder: 0x17d070>
2010-05-31 17:28:44.096 Sam[6677:207] geocoder released
2010-05-31 17:28:44.437 Sam[6677:207] ===> is not set yet // Use of the Location String that is not built yet
2010-05-31 17:28:44.759 Sam[6677:207] geocoder = <MKReverseGeocoder: 0x1714e0>
2010-05-31 17:28:44.783 Sam[6677:207] geocoder released
2010-05-31 17:28:45.174 Sam[6677:207] -----> Las Vegas, Nevada, US // Location string is built here (a little late)
2010-05-31 17:28:45.181 Sam[6677:207] Location manager released
2010-05-31 17:28:47.035 Sam[6677:207] fromSendButton: NO
2010-05-31 17:29:22.884 Sam[6677:207] Location manager initialized // Try 2.
2010-05-31 17:29:22.982 Sam[6677:207] geocoder = <MKReverseGeocoder: 0x15ff10>
2010-05-31 17:29:22.989 Sam[6677:207] geocoder released
2010-05-31 17:29:23.541 Sam[6677:207] -----> Las Vegas, Nevada, US // Location String is built in time
2010-05-31 17:29:23.544 Sam[6677:207] Location manager released
2010-05-31 17:29:24.502 Sam[6677:207] ===> Las Vegas, Nevada, US // and is available to the user of the string
2010-05-31 17:29:25.810 Sam[6677:207] fromSendButton: NO
How can the execution sequence be guaranteed to be in a particular order? Should I put a sleep in the consumer, so that the delegate has time to finish it's job?
Sam!

Answer 1

Shnaps wrote:
The consumer of the location string then accesses it later on. ...
How can the execution sequence be guaranteed to be in a particular order?
I don't think I have enough info to understand your requirement, Sam. You say the consumer runs "later on", but you need to prevent it from running too soon. What needs to happen between the time the geocoder finishes and the comsumer starts? Or to put it another way, why can't the consumer simply be started by reverseGeocoder:didFindPlacemark:?
Should I put a sleep in the consumer, so that the delegate has time to finish it's job?
Only as a last resort. In that case you wouldn't want the consumer to literally sleep, you'd probably want to set a boolean ivar from reverseGeocoder:didFindPlacemark:. When the consumer needed to run, it would start polling that ivar (i.e. start a repeating timer whose fired method would either cancel the timer and start the consumer when the ivar became True, or else raise a timeout alert).
But as above, polling should be your last choice. Even if the consumer is waiting on some additional asynchronous event(s), so long as you can get a message at the end of each event, you should be able to avoid polling by using the last such message to start your consumer.
\- Ray