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Initialize NSMutableDictionary

I am developing an iOS app that I want to use NSMutableDictionary

. Basically what I am doing is converting Java code to objectC.

So, in java, I have something like this:

Map<String, ClassA> dict1 = new HashMap<>();
Map<Integer,Character> dict2 = new HashMap<>();
Map<Integer, Map<String,String>> dict3 = new HashMap<>();

Can anyone please guide me as what would be the equivalent Obj-C code for the above three lines using NSMutableDictionary

as well as how can I set and get pairs to / from dictionaries.

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2 answers


The Objective-C collection classes are not strongly typed, so all three dictionaries will be created with:

NSMutableDictionary *dictX = [NSMutableDictionary new];

To populate the dictionary use [NSMutableDictionary setObject:forKey:]

:



[dict1 setObject:classAInstance
          forKey:@"key1"];
[dict2 setObject:[NSString stringWithFormat:@"%c", character]
          forKey:@(1)];
[dict3 setObject:@{ @"innerKey" : @"innerValue" }
          forKey:@(2)];

and etc.

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Since Objective C has no generic types, all you need to type is:

NSMutableDictionary *dict1 = [[NSMutableDictionary alloc] init];
NSMutableDictionary *dict2 = [[NSMutableDictionary alloc] init];
NSMutableDictionary *dict3 = [[NSMutableDictionary alloc] init];

There are several ways to get and set values. The shorthand form is very similar to array access. To set a value with a reduction:

dict1[@"key"] = @"value";


To get the abbreviated value:

NSString *value = dict1[@"key"];

More detailed syntax looks like this:

[dict1 setObject:@"value" forKey:@"key"];
NSString *value = [dict1 valueForKey:@"key"];
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