App crashing when trying to setValue in NSMuableDictionary

Question

My app is crashing when I try to set value in NSMutableDictionary.

Here is the code below which demostrate the crash, I am not able to find out any crash log also in the console.

NSArray *b =[[a objectAtIndex:1] valueForKey:@"value"];
NSMutableDictionary *b1 =[b objectAtIndex:0];
NSString *str = self.tes;
[b1 setValue:str forKey:@"value"];

Please help me regarding this.

b1 Dictionary log

{
    question = "vale";
    type = a;
}

NSMutableDictionary *b1 = [NSMutableDictionary alloc] initWithDictionary:[b objectAtIndex:0]]; Try this — jogshardik, Jul 17 '15 at 06:38
its is using common memory location for accessing data and updating the values in the same memory location. we cannot alloc init the dictionary — Gaurav Parmar, Jul 17 '15 at 06:40
[b1 setValue:"yourvalue" forKey:"question"] @GauravParmar because there is no key like value !!! — Ashish Kakkad, Jul 17 '15 at 06:41
are you sure that b1 is a dictionary and not just a JSON dict — villy393, Jul 17 '15 at 06:43
What message does the crash print to debugger? Try logging `b1.class` to see whether it is really mutable. — Tricertops, Jul 17 '15 at 06:49
So what is the error message? The reason of the crash? Unrecognized selector? Undefined key? EXC_BAD_ACCESS? There must be something. — Tricertops, Jul 17 '15 at 06:56
Ouch, that sounds like the problem is not in this code. Try enabling Zombies in Scheme. — Tricertops, Jul 17 '15 at 07:10

score 4 · Answer 1 · edited May 23 '17 at 11:43

4

setValue:forKey: is part of the NSKeyValueCoding protocol, which among other things, lets you access object properties from the likes of Interface Builder. setValue:forKey: is implemented in classes other than NSDictionary.

setObject:forKey: is NSMutableDictionary's reason to exist. Its signature happens to be quite similar to setValue:forKey:, but is more generic (e.g. any key type).

So in your case just replace all setValue:forKey with setObject:forKey and valueForKey: with objectForKey:

--

Difference between objectForKey and valueForKey?

edited May 23 '17 at 11:43

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answered Jul 17 '15 at 06:40

arturdev

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Using `setValue:forKey:` is actualy safer, because it handles `nil` values by removing the key. On the other side, `setObject:forKey:` would throw exception and probably crash the app. – Tricertops Jul 17 '15 at 06:48
I prefer to handle `nil` values rather than collect a strange bugs :) – arturdev Jul 17 '15 at 07:01
What bugs? It’s defined and documented behavior of `NSMutableDictionary`. Also makes sense: if you set `nil` for `@"key"`, then getting value for `@"key"` should be `nil` (non-existent). – Tricertops Jul 17 '15 at 07:09

score 0 · Answer 2 · edited May 23 '17 at 12:06

0

So you said you are getting EXC_BAD_ACCESS crash. Try turning on Zombies in Xcode’s Scheme editor. See Enable and Debug Zombie objects in iOS using Xcode 5.1.1. That question explains how to use it, but you don’t need to run Instruments as mentioned there.

Then just run the app and Xcode will show you the reason of EXC_BAD_ACCESS. Don’t forget to turn Zombies off after you don’t need it.

The name Zombie comes from the fact that under this mode all deallocated objects will be marked and will be kept as special regions of memory (not live, not dead, zombies). Once your code attempts to use such deallocated object, Xcode will notice and print helpful message.

edited May 23 '17 at 12:06

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answered Jul 17 '15 at 07:29

Tricertops

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enabling zoombie also not provided any solution to me.. :( – Gaurav Parmar Jul 17 '15 at 09:51
i think the issue is with memory allocation in the ios. can you check with that? – Gaurav Parmar Jul 17 '15 at 12:08

App crashing when trying to setValue in NSMuableDictionary

2 Answers2