How can we store into an NSDictionary? What is the difference between NSDictionary and NSMutableDictionary?

Question

I am developing an application in which I want to use an NSDictionary. Can anyone please send me a sample code explaining the procedure how to use an NSDictionary to store Data with a perfect example?

Answer 1

The NSDictionary and NSMutableDictionary docs are probably your best bet. They even have some great examples on how to do various things, like...

...create an NSDictionary

NSArray *keys = [NSArray arrayWithObjects:@"key1", @"key2", nil]; NSArray *objects = [NSArray arrayWithObjects:@"value1", @"value2", nil]; NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects                                                         forKeys:keys];

...iterate over it

for (id key in dictionary) {     NSLog(@"key: %@, value: %@", key, [dictionary objectForKey:key]); }

...make it mutable

NSMutableDictionary *mutableDict = [dictionary mutableCopy];

Note: historic version before 2010: [[dictionary mutableCopy] autorelease]

...and alter it

[mutableDict setObject:@"value3" forKey:@"key3"];

...then store it to a file

[mutableDict writeToFile:@"path/to/file" atomically:YES];

...and read it back again

NSMutableDictionary *anotherDict = [NSMutableDictionary dictionaryWithContentsOfFile:@"path/to/file"];

...read a value

NSString *x = [anotherDict objectForKey:@"key1"]; 

...check if a key exists

if ( [anotherDict objectForKey:@"key999"] == nil ) NSLog(@"that key is not there"); 

...use scary futuristic syntax

From 2014 you can actually just type dict[@"key"] rather than [dict objectForKey:@"key"]

Answer 2

NSDictionary   *dict = [NSDictionary dictionaryWithObject: @"String" forKey: @"Test"]; NSMutableDictionary *anotherDict = [NSMutableDictionary dictionary];  [anotherDict setObject: dict forKey: "sub-dictionary-key"]; [anotherDict setObject: @"Another String" forKey: @"another test"];  NSLog(@"Dictionary: %@, Mutable Dictionary: %@", dict, anotherDict);  // now we can save these to a file NSString   *savePath = [@"~/Documents/Saved.data" stringByExpandingTildeInPath]; [anotherDict writeToFile: savePath atomically: YES];  //and restore them NSMutableDictionary  *restored = [NSDictionary dictionaryWithContentsOfFile: savePath];