Correcting a plist with dictionaries - objective-c

Question

Plist is copyed to documents directory if it doesn't exist.
If it already exists, I want to use the "Name" key from NSDictionary in bundleArray to find the matching NSDictionary in documentsArray.
When the match is found, I want to check for changes in the strings and replace them if there is a change.
If a match is not found it means this dictionary must be added to documents plist.
This is my code:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[self managePlist];
return YES;
}
- (void)managePlist {
NSError *error;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:#"Objects.plist"];
NSString *bundle = [[NSBundle mainBundle] pathForResource:#"Objects" ofType:#"plist"];
NSFileManager *fileManager = [NSFileManager defaultManager];
if (![fileManager fileExistsAtPath: path]) {
[fileManager copyItemAtPath:bundle toPath:path error:&error];
} else {
NSArray *bundleArray = [[NSArray alloc] initWithContentsOfFile:bundle];
NSMutableArray *documentArray = [[NSMutableArray alloc] initWithContentsOfFile:path];
BOOL updateDictionary = NO;
for(int i=0;i<bundleArray.count;i++) {
NSDictionary *bundleDict=[bundleArray objectAtIndex:i];
BOOL matchInDocuments = NO;
for(int ii=0;ii<documentArray.count;ii++)
{
NSMutableDictionary *documentDict = [documentArray objectAtIndex:ii];
NSString *bundleObjectName = [bundleDict valueForKey:#"Name"];
NSString *documentsObjectName = [documentDict valueForKey:#"Name"];
NSRange range = [documentsObjectName rangeOfString:bundleObjectName options:NSCaseInsensitiveSearch];
if (range.location != NSNotFound) {
matchInDocuments = YES;
}
if (matchInDocuments) {
if ([bundleDict objectForKey:#"District"] != [documentDict objectForKey:#"District"]) {
[documentDict setObject:[bundleDict objectForKey:#"District"] forKey:#"District"];
updateDictionary=YES;
}
}
else {
[documentArray addObject:bundleDict];
updateDictionary=YES;
}
}
}
if(updateDictionary){
[documentArray writeToFile:path atomically:YES];
}
}
}
If I run my app now I get this message: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'
How can I fix this?
When this is fixed, do you think my code will work?
If not, I would be happy for some suggestions on how to do this. I have struggled for a while and really need to publish the update with the corrections! Thanks a lot for your help.

Answer 1

Presumably the documentDict is actually immutable. Even though you assign it to an NSMutableDictionary, this doesn't accurately describe the underlying data.
NSMutableDictionary *documentDict = [documentArray objectAtIndex:ii];
should be:
NSMutableDictionary *documentDict = [NSMutableDictionary dictionaryWithDictionary:[documentArray objectAtIndex:ii]];
and wherever you edit the documentDict, add:
[documentArray replaceObjectAtIndex:ii withObject:documentDict];

Answer 2

When you read a plist from file, an immutable dictionary/array with immutable children is created, so your
  NSMutableDictionary *documentDict = [documentArray objectAtIndex:ii];
line is erfectively a lie - you don't have a mutable dictionary. To create a mutable object from a plist, have a look at CFPropertyListCreateWithData and specify kCFPropertyListMutableContainersAndLeaves as the mutability option.

Answer 3

This is my final and working code using the answer from James Webster. Thanks to H2CO3 as well for contribution.
- (void)managePlist {
NSError *error;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:#"Object.plist"];
NSString *bundle = [[NSBundle mainBundle] pathForResource:#"Object" ofType:#"plist"];
NSFileManager *fileManager = [NSFileManager defaultManager];
if (![fileManager fileExistsAtPath:path]) {
[fileManager copyItemAtPath:bundle toPath:path error:&error];
}
else
{
NSArray *bundleArray = [[NSArray alloc] initWithContentsOfFile:bundle];
NSMutableArray *documentArray = [[NSMutableArray alloc] initWithContentsOfFile:path];
BOOL updateDictionary = NO;
for(int i=0;i<bundleArray.count;i++) {
NSDictionary *bundleDict=[bundleArray objectAtIndex:i];
for(int ii=0;ii<documentArray.count;ii++)
{
NSMutableDictionary *documentDict = [NSMutableDictionary dictionaryWithDictionary:[documentArray objectAtIndex:ii]];
NSString *bundleObjectName = [bundleDict valueForKey:#"Name"];
NSString *documentsObjectName = [documentDict valueForKey:#"Name"];
NSRange range = [documentsObjectName rangeOfString:bundleObjectName options:NSCaseInsensitiveSearch];
if (range.location != NSNotFound) {
NSString *districtString = [bundleDict objectForKey:#"District"];
if ([documentDict objectForKey:#"District"] != districtString) {
[documentDict setObject:districtString forKey:#"District"];
[documentArray replaceObjectAtIndex:ii withObject:documentDict];
updateDictionary=YES;
}
}
}
}
if(updateDictionary){
[documentArray writeToFile:path atomically:YES];
}
}
}