CODEWITHSUNDEEP
iphoneobjective-ciosnsdictionary
Vibol
Vibol

Reputation: 1168

Manage data (object, key) in objective C

I want to save some object in form of collection (object,key) in objective C. I found NSMutableDictionary is the fit to that, but the problem is that I cannot get back the object I want (last added object, first added object ...). Is there a better way of doing so?

Upvotes: 1

Views: 182

Answers (4)

Vivek Rajanna
Vivek Rajanna

Reputation: 86

NSMutablearray is best approach if you want to get last added object , or object by index . object added first is at object index 0 and object added last in at [count-1] index

Upvotes: 0

Quang Hà
Quang Hà

Reputation: 4744

You can get back your object by using this object's key you added to Dictionary:

NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:@"A" forKey:@"a"];

NSString *strA = [dict objectForKey:@"a"];

Put your keys to an NSMutableArray will help you get last/first key.

Hope that help!

Upvotes: 1

Analog File
Analog File

Reputation: 5316

Dictionaries are for accessing data when you have a key. They are not ordered containers.

If you need to retrieve data based on when you added it to a container you need a LIFO (aka stack), FIFO (aka queue) or deque (aka double-ended queue) kind of container. You can read about them on wikipedia for a starter, but I suggest you read at least one decent algorithm and data structures book, if you want to become a programmer.

AFAIK there are no predefined classes that implement those abstractions in cocoa, but they are all easy to do with arrays. NSArray has lastObject and objectAtIndex: methods, and NSMutableArray also have addObject:, insertObject:atIndex:, removeLastObject and removeObjectAtIndex: methods that basically are the primitives for LIFO/FIFO/deque access (assuming you use 0 when an index is required by those methods).

Upvotes: 0

wjl
wjl

Reputation: 7351

For a Key-Value pair, an NSDictionary or NSMutableDictionary is the correct solution.

There will only be one value for any given key, and setting a new value will overwrite the old one.

NSMutableDictionary *myDictionary = [[NSMutableDictionary alloc] init];
[myDictionary setValue:@"World" forKey:@"Hello"];
NSLog(@"Hello %@", [myDictionary objectForKey:@"Hello"]); // prints Hello World
[myDictionary setValue:@"StackOverflow" forKey:@"Hello"];
NSLog(@"Hello %@", [myDictionary objectForKey:@"Hello"]); // prints Hello StackOverflow
[myDictionary setValue:nil forKey:@"Hello"];
NSLog(@"Hello %@", [myDictionary objectForKey:@"Hello"]); // prints Hello (null)

Upvotes: 1

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