Question

i have looked all over the place regarding this problem. All i am trying to do is, create a nsuser defaults object, then add a mutable array to it and try to modify the nsuserdefaults object.

//Created a sample array
NSMutableArray *xml=[[NSMutableArray alloc] init];
[xml addObject:@"x"];
[xml addObject:@"x"];
[xml addObject:@"x"];
[xml addObject:@"x"];
[xml addObject:@"x"];
//assigned to defaults object which is created previously with a mutableCopy
[defaults  setObject:[xml mutableCopy] forKey:@"userLocationsDetailedXML"]; 
//Tried to modify the defaults object - which at this point should be mutable
[[defaults objectForKey:@"userLocationsDetailedXML" ] replaceObjectAtIndex:1 withObject:@"y"] ;

Adding [defaults synchronize] does’nt help either.

But surprisingly the defaults object is still immutable. It is __NSCFArray, not __NSCFArrayM as expected
Any suggestions?

edit: console output
Class : __NSCFArray => SHould’nt it be _NSCFArrayM since i created a mutable copy?
[_NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object’

Answer 1

Try casting the array as NSMutableArray, using

[(NSMutableArray *)[defaults objectForKey:@"userLocationsDetailedXML"] replaceObjectAtIndex:1 withObject:@"y"] ;

that should take care of it.

EDIT:

Given that you can’t actually store NSMutableArrays in NSUserDefaults, I recommend that you just go ahead and reassign the entire thing, like so:

NSMutableArray *xml = [[NSMutableArray alloc] init];
    [xml addObject:@"x"];
    [xml addObject:@"x"];
    [xml addObject:@"x"];
    [xml addObject:@"x"];
    [xml addObject:@"x"];

[defaults  setObject:xml forKey:@"userLocationsDetailedXML"]; 
[xml release];

Then, for changing the values,

NSMutableArray *userLoc = [[defaults objectForKey:@"userLocationsDetailedXML"] mutableCopy];
[userLoc replaceObjectAtIndex:1 withObject:@"y"];
[defaults  setObject:userLoc forKey:@"userLocationsDetailedXML"]; 
[userLoc release]; //thanks, dreamlax!