ios - App crashing when trying to setValue in NSMuableDictionary -

my app crashing when try set value in nsmutabledictionary.

here code below demostrate crash, not able find out crash log in console.

nsarray *b =[[a objectatindex:1] valueforkey:@"value"]; nsmutabledictionary *b1 =[b objectatindex:0]; nsstring *str = self.tes; [b1 setvalue:str forkey:@"value"]; 

please me regarding this.

b1 dictionary log

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

setvalue:forkey: part of nskeyvaluecoding protocol, among other things, lets access object properties likes of interface builder. setvalue:forkey: implemented in classes other nsdictionary.

setobject:forkey: nsmutabledictionary's reason exist. signature happens quite similar setvalue:forkey:, more generic (e.g. key type).

so in case replace setvalue:forkey setobject:forkey , valueforkey: objectforkey:

--

difference between objectforkey , valueforkey?