Nsdictionary and Nsmutabledictionary

Nsdictionary

1: What is a dictionary?

Nsdictionary in OC: value is found based on key, and everything stored in the dictionary is a key-value pair

2: How do I create a dictionary?

Method One:

Nsdictionary *dict = [nsdictionary dictionarywithobject:@ "lnj" forkey:@ "  Name"]; // get value based on key NSString *name = [dict objectforkey:@ "name"]; NSLog (@ "name =%@", name);

Method Two:

/

/Note: Key and value are one by one corresponding nsdictionary*dict = [Nsdictionary dictionarywithobjects:@[@"LNJ",@" -",@"1.75"] Forkeys:@[@"name",@" Age",@"Height"]]; NSLog (@"%@ %@ %@", [Dict Objectforkey:@"name"], [dict objectforkey:@" Age"], [dict objectforkey:@"Height"]); method Three:"Shorthand:nsdictionary*dict =@{key:value}; Nsdictionary*dict = @{@"name":@"LNJ"}; NSLog (@"%@", dict[@"name"]); Nsdictionary*dict = @{@"name":@"LNJ",@" Age":@" -",@"Height":@"1.75"}; NSLog (@"%@ %@ %@", dict[@"name"], dict[@" Age"], dict[@"Height"]);

3: How do I traverse a dictionary?

Nsdictionary *dict = @{@"name":@"LNJ",@" Age":@" -",@"Height":@"1.75"};//gets the number of keys and value in the dictionary, which is called the key in the dictionary and value is calledNSLog (@"count =%lu", [dict Count]);

Method one: old-fashioned for loop notation

 for (int0; i < Dict.count; + +i)    {//  get all keys in the dictionary    nsarray *keys = [Dict AllKeys];     // remove key    from current position //         NSLog (@ "%@", Keys[i]);    NSString *key = keys[i];     *value = Dict[key];    NSLog (@ "key =%@, value =%@", key, value);}

Method Two: Enhance the For loop notation

// How to traverse the dictionary through Forin will assign all keys to the previous obj  for inch dict) {    //        NSLog (@ "%@", key);    NSString *value = Dict[key];    NSLog (@ "key =%@, value =%@", key, value);}

Method Three: An iterator to the OC dictionary to traverse

[Dict enumeratekeysandobjectsusingblock:^ (ID-ID obj, BOOL *stop) {    NSLog (@ " key =%@, value =%@ " , key, obj);}];

4: How to read and write a dictionary file?

1. Writing dictionary data to a file

Nsdictionary *dict = @{@ "name":@ "lnj"@ "age  ":@"@"height":@ " 1.75 " }; [Dict writetofile: @" /users/xiaomage/desktop/info.plist [ Atomically:yes];

2. Reading the dictionary data from the file

• Note: Dictionaries and arrays are different, and the data stored in the dictionary is unordered

Nsdictionary *newdict = [nsdictionary dictionarywithcontentsoffile:@ "/users/xiaomage/desktop/ Info.plist"]; NSLog (@ "%@"*arr = @[@, @ +, @ @5 ]; [Arr writetofile: @" /users/xiaomage/desktop/abc.plist [ Atomically:yes];

9.NSMutableDictionary

How to increase and revise a variable dictionary

1: How do I create an empty mutable dictionary?

Nsmutabledictionary *DICTM = [Nsmutabledictionary dictionary];

2: How do I add a key value pair to a mutable dictionary?

[DICTM SetObject:@"LNJ"Forkey:@"name"];//Shorthand:dictm[@"name"] =@"LNJ";//all key-value pairs in the incoming dictionary are removed to add to the DICTM[DICTM setvaluesforkeyswithdictionary:@{@" Age":@" -",@"Height":@"1.75"}];

3: How do I get the value of a mutable dictionary based on the key?

NSLog (@ "name =%@", dictm[@ "name"]);

4: How do I delete a variable dictionary key value pair?

[DICTM Removeobjectforkey:@ "name"]; [DICTM removeobjectsforkeys:@[@"Age"@ "height"]];

5: How do I modify a key-value pair in a mutable dictionary?

• Using the SetObject method to assign a value to a key of the same name, the new value overwrites the old value

[DICTM setobject:@ " forkey":@ "Age"]; // abbreviation:dictm[@"Age"@ "the";

6: What are the considerations for using a mutable dictionary?

1. Cannot use @{} to create a mutable dictionary

    Nsmutabledictionary *DICTM = @{@ "name":@ "lnj"}; // compile will be an error    [DICTM setobject:@ "Forkey":@ "Age"];

2.

• If it is an immutable dictionary, then key cannot be the same
• If there is a key with the same name in the immutable dictionary, then the value corresponding to the key will not be saved
• If it is in a mutable array, the following will overwrite the previous

Nsdictionary *dict = @{@"name":@"LMJ",@"name":@"LNJ"}; NSLog (@"dict =%@", Dict); Nsmutabledictionary*DICTM = [Nsmutabledictionary dictionarywithobjects:@[@"LMJ",@"LNJ"] Forkeys:@[@"name",@"name"]]; NSLog (@"dict =%@", DICTM);

Nsdictionary and Nsmutabledictionary