Question

I have a property list which I read into an NSDictionary, from which I would like to create a mutable copy into an NSMutableDictionary to edit the contents and – later be able to reset the mutable dictionary by copying back the original contents.

NSDictionary *defaultRows;
NSMutableDictionary *rows;

NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"Config" ofType:@"plist"];
defaultRows = [[[NSDictionary alloc] initWithContentsOfFile: plistPath] objectForKey:@"rows"];

This is how I try to create a copy of the original dictionary (according to Apple’s recommendation):

rows = [NSMutableDictionary dictionaryWithDictionary: defaultRows];

When I try to change the contents of the dictionary rows with:

[[[rows objectForKey:self.company.coaTypeCode] objectForKey:statementType] removeObjectsAtIndexes:rowsToDelete];

I get the runtime error *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'.

I have read the article here, but wonder if there is a more elegant method to implement a deep copy?

Answer 1

Since you are loading defaultRows from a property list, the easiest way to do this is to just deserialize the property list with mutable containers.

NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"Config" ofType:@"plist"];
NSData *rowsData = [NSData dataWithContentsOfFile:plistPath];

NSMutableDictionary *rows = [NSPropertyListSerialization propertyListWithData:rowsData
    options:NSPropertyListMutableContainers format:NULL error:NULL];