Dictionary classes in Objective-c

A dictionary is a collection of data that holds a mapping relationship (Key-value pairs). A key-value is considered an entry (Entry), and the dictionary is a container for storing key-value pairs.

Features of the Dictionary class

Unlike arrays, dictionaries access elements by key;

The key value cannot be duplicated, and value must be an object;

Key-value pairs are stored in the dictionary in unordered order.

Dictionaries are divided into immutable dictionaries (nsdictionary) and variable dictionaries (nsmutabledictionary).

Immutable Dictionary (nsdictionary)

Once a dictionary is created, key-value pairs cannot be changed, cannot be added, and cannot be deleted.

Only key or value can be read.

Create a Dictionary object

1 nsdictionary *dic1 = [nsdictionary dictionarywithobject:@ " Zhang San " forkey:@ "  name"]; 2 NSLog (@ "dic1%@", Dic1);

Create a dictionary with multiple key-value pairs

1Nsdictionary *dic2 = [Nsdictionary Dictionarywithobjectsandkeys:@"a",@"1",@"b",@"2",@"C",@"3", nil];2NSLog (@"Dic2%@", dic2);3 //get all the keys4NSLog (@"Key%@", Dic2.allkeys);5 //get all the value6NSLog (@"value%@", dic2.allvalues);7 //find value by key8 //get the corresponding value based on key9NSLog (@"Object%@", [Dic2 Objectforkey:@"2"]);

Variable dictionary (nsmutabledictionary)

Create a mutable dictionary

 1  nsmutabledictionary *mdic = [ Nsmutabledictionary dictionary];  2  [mDic setobject:@ " lilei   forkey:@"  name   ";  3  [mDic setobject:@ " m   forkey:@"  sex   ";  4  NSLog (@ " mdic%@  , MDic); 

Add/Modify Key-value to

1 //add Key-value When key is not present2 //when key is present, find the corresponding key to replace the value content .3[MDic SetObject:@"Lilei"Forkey:@"name"];4[MDic SetObject:@"male"Forkey:@"Sex"];5NSLog (@"MDic%@", mDic);6 //Modify7[MDic SetObject:@"Hanmeimei"Forkey:@"name"];8NSLog (@"MDic%@", MDic);

Delete Dictionary

1 // Delete 2 [mDic removeobjectforkey:@ "name"]; 3 NSLog (@ "mDic%@", MDic);

Traverse Dictionary

1 //Traverse Dictionary2Nsdictionary *dic = [Nsdictionary Dictionarywithobjectsandkeys:@"Lilei",@"name",@"male",@"Sex",@" -",@" Age", nil];3NSLog (@"DiC%@", DIC);4Nsarray *ARR1 =Dic.allkeys;5  for(Nsinteger i =0; i < Arr1.count; i++) {6 //get each key value7NSString *key =[arr1 objectatindex:i];8 //get the corresponding value based on key9NSLog (@"key:%@, Value:%@", Key, [dic Objectforkey:key]);Ten}

Dictionary classes in Objective-c