CODEWITHSUNDEEP
objective-cnsdictionaryenumerationnsmutabledictionarykey-value
sagarkothari
sagarkothari

Reputation: 24810

for each loop in Objective-C for accessing NSMutable dictionary

I am finding some difficulty in accessing mutable dictionary keys and values in Objective-C.

Suppose I have this:

NSMutableDictionary *xyz=[[NSMutableDictionary alloc] init];

I can set keys and values. Now, I just want to access each key and value, but I don't know the number of keys set.

In PHP it is very easy, something as follows:

foreach ($xyz as $key => $value)

How is it possible in Objective-C?

Upvotes: 285

Views: 269011

Answers (7)

zneak
zneak

Reputation: 138041

for (NSString* key in xyz) {
    id value = xyz[key];
    // do stuff
}

This works for every class that conforms to the NSFastEnumeration protocol (available on 10.5+ and iOS), though NSDictionary is one of the few collections which lets you enumerate keys instead of values. I suggest you read about fast enumeration in the Collections Programming Topic.

Oh, I should add however that you should NEVER modify a collection while enumerating through it.

Upvotes: 689

Laurent Etiemble
Laurent Etiemble

Reputation: 27889

I suggest you to read the Enumeration: Traversing a Collection’s Elements part of the Collections Programming Guide for Cocoa. There is a sample code for your need.

Upvotes: 5

Avinash
Avinash

Reputation: 4362

The easiest way to enumerate a dictionary is 

for (NSString *key in tDictionary.keyEnumerator) 
{
    //do something here;
}

where tDictionary is the NSDictionary or NSMutableDictionary you want to iterate.

Upvotes: 5

Brody Robertson
Brody Robertson

Reputation: 8604

If you need to mutate the dictionary while enumerating:

for (NSString* key in xyz.allKeys) {
    [xyz setValue:[NSNumber numberWithBool:YES] forKey:key];
}

Upvotes: 16

gcamp
gcamp

Reputation: 14662

You can use -[NSDictionary allKeys] to access all the keys and loop through it.

Upvotes: 2

dreamlax
dreamlax

Reputation: 95335

Fast enumeration was added in 10.5 and in the iPhone OS, and it's significantly faster, not just syntactic sugar. If you have to target the older runtime (i.e. 10.4 and backwards), you'll have to use the old method of enumerating:

NSDictionary *myDict = ... some keys and values ...
NSEnumerator *keyEnum = [myDict keyEnumerator];
id key;

while ((key = [keyEnum nextObject]))
{
    id value = [myDict objectForKey:key];
    ... do work with "value" ...
}

You don't release the enumerator object, and you can't reset it. If you want to start over, you have to ask for a new enumerator object from the dictionary.

Upvotes: 3

Quinn Taylor
Quinn Taylor

Reputation: 44769

Just to not leave out the 10.6+ option for enumerating keys and values using blocks...

[dict enumerateKeysAndObjectsUsingBlock:^(id key, id object, BOOL *stop) {
    NSLog(@"%@ = %@", key, object);
}];

If you want the actions to happen concurrently:

[dict enumerateKeysAndObjectsWithOptions:NSEnumerationConcurrent
                              usingBlock:^(id key, id object, BOOL *stop) {
    NSLog(@"%@ = %@", key, object);
}];

Upvotes: 102

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