A preliminary knowledge of Objective-c dictionary

The dictionary stores key-value pairs, and values can be obtained by keys

 

1. Create an immutable dictionary

1 // 1 f (1)
2 NSDictionary * dic = [[NSDictionary alloc] initWithObjectsAndKeys: @ "one", @ "1", @ "two", @ "2", @ "three", @ "3", nil];
3 NSLog (@ "% @", dic);
4
5 // 2 Quickly create a dictionary
6 NSDictionary * dic2 = @ {@ "1": @ "one", @ "2": @ "two", @ "3": @ "three"};
7 NSLog (@ "% @", dic2);
2. The number of elements in the dictionary

 1 NSUInteger count = [dic2 count];

2 NSLog (@ "% lu", count);

 

3. Arrays can be stored in the dictionary

1 NSArray * arr = @ [@ "one", @ "two", @ "three"];
2 NSDictionary * dic3 = @ {@ "1": @ "one", @ "array": arr, @ "2": @ "two"};
3 NSLog (@ "% @", dic3);
 

4. The value in the dictionary

1 // 5 Take the value from the dictionary
2 NSArray * arr2 = [dic3 objectForKey: @ "array"];
3 NSLog (@ "% @", arr2);
4 // Quick access
5 NSArray * arr3 = dic3 [@ "array"];
6 NSLog (@ "% @", arr3);
 

5. Variable dictionary

5.1 Creation of variable dictionary

1 // Create
2 NSMutableDictionary * muDic = [[NSMutableDictionary alloc] initWithObjectsAndKeys: @ "one", @ "1", @ "two", @ "2", nil];
3
4 NSDictionary * dic = @ {@ "1": @ "one", @ "2": @ "two"};
5
6 NSMutableDictionary * muDic2 = [[NSMutableDictionary alloc] initWithDictionary: dic];
7
8 NSLog (@ "% @", muDic2);
 

5.2 Add elements to the dictionary

1 [muDic2 setObject: @ "three" forKey: @ "3"];
2 NSLog (@ "% @", muDic2);
5.3 Reset dictionary (set method)

1 [muDic2 setDictionary: @ {@ "a": @ "one", @ "b": @ "two"}];
2 NSLog (@ "% @", muDic2);
5.4 Delete element

Delete key-value pairs corresponding to key

 1 [muDic2 removeObjectForKey: @ "a"];

2 NSLog (@ "% @", muDic2);

Delete all

 1

2 [muDic2 removeAllObjects];
3 NSLog (@ "% @", muDic2);

5.5 Print the elements in the dictionary

1 NSArray * arr = [muDic2 allKeys];
2 // arr stores all keys in the dictionary
3 NSLog (@ "% @", arr);
4 // Print the values in the dictionary muDic by fast enumeration
5 for (NSString * str in arr) {
6 // NSLog (@ "% @", [muDic2 objectForKey: str]);
7 NSLog (@ "% @", muDic2 [str]);
8         }
 

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-(BOOL) isKindOfClass: (Class) aClass;

Determine whether it is a certain type

example

[obj isKindOfClass: [NSString class]];

Determine if obj is of type NSString and return value is of type BOOL

 

Understanding the Objective-C dictionary