R – NSMutable Dictionary adding objects

nsmutabledictionaryobjective c

Is there a more efficient way to add objects to an NSMutable Dictionary than simple iteration?

Example:

// Create the dictionary

NSMutableDictionary *myMutableDictionary = [NSMutableDictionary dictionary];    

// Add the entries

[myMutableDictionary setObject:@"Stack Overflow" forKey:@"http://stackoverflow.com"];
[myMutableDictionary setObject:@"SlashDotOrg" forKey:@"http://www.slashdot.org"];
[myMutableDictionary setObject:@"Oracle" forKey:@"http://www.oracle.com"];

Just curious, I'm sure that this is the way it has to be done.

Best Answer

If you have all the objects and keys beforehand you can initialize it using NSDictionary's:

dictionaryWithObjects:forKeys:

Of course this will give you immutable dictionary not mutable. It depends on your usage which one you need, you can get a mutable copy from NSDictionary but it seems easier just to use your original code in that case:

NSDictionary * dic = [NSDictionary dictionaryWith....];
NSMutableDictionary * md = [dic mutableCopy];
... use md ...
[md release];

Compare method

Either you implement a compare-method for your object:

- (NSComparisonResult)compare:(Person *)otherObject {
    return [self.birthDate compare:otherObject.birthDate];
}

NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(compare:)];

NSSortDescriptor (better)

or usually even better:

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"birthDate"
                                           ascending:YES];
NSArray *sortedArray = [drinkDetails sortedArrayUsingDescriptors:@[sortDescriptor]];

You can easily sort by multiple keys by adding more than one to the array. Using custom comparator-methods is possible as well. Have a look at the documentation.

Blocks (shiny!)

There's also the possibility of sorting with a block since Mac OS X 10.6 and iOS 4:

NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(Person *a, Person *b) {
    return [a.birthDate compare:b.birthDate];
}];

Performance

The -compare: and block-based methods will be quite a bit faster, in general, than using NSSortDescriptor as the latter relies on KVC. The primary advantage of the NSSortDescriptor method is that it provides a way to define your sort order using data, rather than code, which makes it easy to e.g. set things up so users can sort an NSTableView by clicking on the header row.

R – How to add multiple keys and values to an NSMutableDictionary without using an array

I'm surprised that code doesn't just crash. See here:

NSURL  *urlA;
urlA = [NSURL URLWithString:surlA]; 
NSURL  *urlB;
urlA = [NSURL URLWithString:@"http://www.apple.com"];

You are assigning to urlA twice and never assigning to urlB. Fix that and you'll see the correct value logged.

Note also that you can do this:

NSLog(@"dictionary: %@", anNSDictionary);

And see all of the key/value pairs in the dictionary.

Best Answer

Related Solutions

Ios – How to sort an NSMutableArray with custom objects in it

Compare method

NSSortDescriptor (better)

Blocks (shiny!)

Performance

R – How to add multiple keys and values to an NSMutableDictionary without using an array

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