NSString包含一个数字，为​​什么它会使我的App崩溃？

Question

I'm having some difficulty with NSString in my application. Basically, I have an NSString called o1string which contains the value "602". I want to output this in a UIAlertView alongside some other text.

votedmessage = [ NSString stringWithFormat:@"The current standings are as follows:\n\n%@: %@ votes", b1title, o1string ];
UIAlertView *votedAlert = [[UIAlertView alloc] initWithTitle:@"Thank you for voting" message:votedmessage delegate:self cancelButtonTitle:nil otherButtonTitles:@"OK", nil];

I have used NSLog and verified that the value inside the NSString is definitely 602, and the other variable (b1title) used in the message outputs fine on its own. I cannot work out why the app is crashing when I add the o1votes variable to the alert message though, is it something to do with a conflict in holding just a number inside an NSString?

This is how o1string is set. It definitely contains "602", grabbed from an XML file.

o1string = [[options objectAtIndex:3] objectForKey: @"votes"];
o1string = [o1string stringByReplacingOccurrencesOfString:@"\n" withString:@""];
o1string = [o1string stringByReplacingOccurrencesOfString:@"    " withString:@""];

Answer 1

Unless that assignment of o1string is in the same method where votedmessage is created (since you don't say, I'm assuming not), it will be gone by the time you get to the code where votedmessage needs it.

Unless you're using garbage collection, you need to retain objects that you want to keep around past the current method. See the Objective-C memory management guide for complete details.

Answer 2

You need to post more code. In particular it's not clear whether the two pieces you posted are in the same function or different places.

If they're in different places you must call [o1string retain] (and later [o1string release]). The easiest way to do this would be to make olstring a property with retain semantics.

stringByReplacingOccurrencesOfString returns a temporary instance that will be auto-released sometime after the function exists.

I would guess the reason b1Title works is that it's stored in your dictionary so is persistent. o1string is created from the stringByXXX functions and is temporary.