How to Use Dictionaries
Like an array, a dictionary is a list of objects. However, dictionaries make it
easier to organize data by providing “keys” that make it a snap to find the
things you put in there. These are sometimes referred to as a hash or a
hash-table.
Instantiate a dictionary
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
Add objects to a dictionary indexed by keys [dictionary setObject:@"A Book about the Letter A" forKey:@"A"]; [dictionary setObject:@"A Book about the Letter B" forKey:@"B"]; [dictionary setObject:@"A Book about the Letter C" forKey:@"C"]; Retrieve an object from a dictionary with a key NSLog([dictionary objectForKey:@"B"]);
Release a dictionary [dictionary release];
Cool – hope you enjoyed this snippet of da codes! Once you get use to the square brackets and verbose parameter prefixes Objective-C starts to feel like the programming languages that you are used to.
{ 1 trackback }
{ 2 comments }
This is a nice introductory.
How about some examples on using Arrays in Dictionaries and how to use them in Table Views?
What is the fastest way to access them, etc.
Using an array is a dictionary is actually the same as using a string in a dictionary. You just stick in an array instead of a string in the setObject message. Here is an example:
//create dictionary
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
//create an array and put something (anything) into the array
NSMutableArray *stuffInList = [[NSMutableArray alloc] init];
[stuffInList addObject:@"Something in a list"];
//put the array into the dictionary
[dictionary setObject:stuffInList forKey:@"Object001"];
//as an example retrieve the array from the dictionary
NSArray *NSTempArray = [dictionary objectForKey:@"Object001"];
//write out the first object in the array to the log
NSLog([NSTempArray objectAtIndex:0]);
As far as using structures like this in a table view. It sort of depends on how you design your data model and that is a big topic that will vary over developers, app and developer+app combinations. However you decided to do it the table view controller delegate methods of interested are:
numberOfSectionsInTableView
numberOfRowsInSection
cellForRowAtIndexPath
These delegate methods all do what they sound like… Hope that helps!
Comments on this entry are closed.