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

User · Accepted Answer

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"]

User · Answer

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

User · Answer

The key difference  NSMutableDictionary can be modified in place  NSDictionary cannot  This is true for all the other NSMutable  classes in Cocoa  NSMutableDictionary is a subclass of NSDictionary  so everything you can do with NSDictionary you can do with both  However  NSMutableDictionary also adds complementary methods to modify things in place  such as the method setObject forKey    You can convert between the two like this   NSMutableDictionary  mutable     dict mutableCopy  autorelease   NSDictionary  dict     mutable copy  autorelease      Presumably you want to store data by writing it to a file  NSDictionary has a method to do this  which also works with NSMutableDictionary    BOOL success    dict writeToFile    file path  atomically YES     To read a dictionary from a file  there s a corresponding method   NSDictionary  dict    NSDictionary dictionaryWithContentsOfFile    file path      If you want to read the file as an NSMutableDictionary  simply use   NSMutableDictionary  dict    NSMutableDictionary dictionaryWithContentsOfFile    file path

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

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