Create a dictionary property list programmatically

Question

I want to programatically create a dictionary which feeds data to my UITableView but I'm having a hard time with it. I want to create a dictionary that resembles this property list (image) give or take a couple of items.

I've looked at "Property List Programming Guide: Creating Property Lists Programmatically" and I came up with a small sample of my own:

//keys

NSArray *Childs = [NSArray arrayWithObjects:@"testerbet", nil];
NSArray *Children = [NSArray arrayWithObjects:@"Children", nil];
NSArray *Keys = [NSArray arrayWithObjects:@"Rows", nil];
NSArray *Title = [NSArray arrayWithObjects:@"Title", nil];

//strings

NSString *Titles = @"mmm training";

//dictionary 

NSDictionary *item1 = [NSDictionary dictionaryWithObject:Childs, Titles forKey:Children , Title];
NSDictionary *item2 = [NSDictionary dictionaryWithObject:Childs, Titles forKey:Children , Title];
NSDictionary *item3 = [NSDictionary dictionaryWithObject:Childs, Titles forKey:Children , Title];
NSArray *Rows = [NSArray arrayWithObjects: item1, item2, item3, nil];
NSDictionary *Root = [NSDictionary dictionaryWithObject:Rows forKey:Keys];

// NSDictionary *tempDict = [[NSDictionary alloc] //initWithContentsOfFile:DataPath];
NSDictionary *tempDict = [[NSDictionary alloc] initWithDictionary: Root];

I'm trying to use this data of hierachy for my table views. I'm actually using this article as an example.

So I was wondering how can I can create my property list (dictionary) programmatically so that I can fill it with my own arrays.

I'm still new with iPhone development so bear with me. ;)

Answer 1

NSMutableDictionary *topLevel = [NSMutableDictionary dictionary];

NSMutableDictionary *item1 = [NSMutableDictionary dictionary];
NSString *item1title = [NSString stringWithString:@"Title 1"];
NSMutableDictionary *item1children = [NSMutableDictionary dictionary];

// create children
NSString *item1child1 = [NSString stringWithString:@"item 1, child 1"];

NSMutableDictionary *item1child2 = [NSMutableDictionary dictionary];
NSString *item1child2title = [NSString stringWithString:@"Title 1-2"];
NSMutableDictionary *item1child2children = [NSMutableDictionary dictionary];

NSString *item1child2child1 = [NSString stringWithString:@"item 1, child 2, child 1"];
NSString *item1child2child2 = [NSString stringWithString:@"item 1, child 2, child 2"];

[item1child2 setObject:item1child2title forKey:@"Title"];
[item1child2children setObject:item1child2child1 forKey:@"item 1 child2 child 1"];
[item1child2children setObject:item1child2child2 forKey:@"item 1 child2 child 2"];

[item1child2 setObject:item1child2children forKey:@"children"];

// add children to dictionary
[item1children setObject:item1child1 forKey:@"item1 child1"];
[item1children setObject:item1child2 forKey:@"item1 child2"];

// add to item 1 dict
[item1 setObject:item1title forKey:@"Title"];
[item1 setObject:item1children forKey:@"children"];

NSMutableDictionary *item2 = [NSMutableDictionary dictionary];
NSString *item2title  = [NSString stringWithString:@"Title"];
NSMutableDictionary *item2children = [NSMutableDictionary dictionary]; 

NSString *item2child1 = [NSString stringWithString:@"item 2, child 1"];
NSString *item2child2 = [NSString stringWithString:@"item 2, child 2"];
NSString *item2child3 = [NSString stringWithString:@"item 2, child 3"];

// add children to dictionary
[item2children setObject:item2child1 forKey:@"item2 child1"];
[item2children setObject:item2child2 forKey:@"item2 child2"];
[item2children setObject:item2child3 forKey:@"item2 child3"];

// add to item 2 dict
[item2 setObject:item2title forKey:@"Title"];
[item2 setObject:item2children forKey:@"children"];

[topLevel setObject:item1 forKey:@"Item 1"];
[topLevel setObject:item2 forKey:@"Item 2"];

Answer 2

This is a situation where "teach a man to fish" is a vastly more helpful approach than "give a man a fish". Once you understand the basic principles and the NSDictionary API, it becomes much easier to craft your own custom solution. Here are a few observations and learning points:

• The method +dictionaryWithObject:forKey: is used to create an NSDictionary with a single key-value pair. It will not accept comma-separated arguments after each colon (:) in the method call, just one. To create a dictionary with multiple key-value pairs, use one of 2 related methods: +dictionaryWithObjects:forKeys: which accepts two NSArray objects containing values and keys, or +dictionaryWithObjectsAndKeys: which alternates (object, key, object, key) with a terminating nil argument.
• Simplify the creation code. You don't need a million local variables just to create the thing. Use inline arguments where it makes sense. One way to do this it to build up your dictionary in code as an NSMutableDictionary, then (if necessary) make an immutable copy of it by calling -copy on it. (Remember that a copy method returns a new object that you must release to avoid memory leaks.) That way you don't have to have a variable for every single value so you can do a "one shot" creation of the structure(s) at each level.
• Use +arrayWithObject: for creating an NSArray with a single object.
• (Style suggestions) Never use an uppercase letter to begin the name of a variable, method, or function. (Notice that SO highlights leading-caps variables like class names.) It will certainly help others who read your code from being confused about your intent by your naming scheme.

Just to give you a flavor of what creating the dictionary in the linked image might look like in code... (I'm ignoring your chosen variable names and using both different approaches for completeness.)

NSDictionary *item1 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"Screen J",[NSNumber numberWithInt:3],nil]
                                                  forKeys:[NSArray arrayWithObjects:@"Title",@"View",nil]];
NSDictionary *item2 = [NSDictionary dictionaryWithObjectsAndKeys:
                                        @"Screen I", @"Title", 
                                        [NSArray arrayWithObject:item1], @"Children", 
                                        nil];
...

Answer 3

first of .. super! thanks .. I really appreciate the explanation and code snippet. Since you gave me such a good explanation I hope you don't mind me asking a couple more questions.

First, I did as you suggested and this is what I came up with : (I used my original property list instead of the example this time so this is where the drilldown table gets his( or needs to get his ) treestructure).

http://img509.imageshack.us/img509/7523/picture2lsg.png

NSDictionary *root = [NSMutableDictionary dictionary];
NSDictionary *item1 = [NSDictionary dictionaryWithObject:[NSArray arrayWithObject:@"VirtuaGym Online"] forKey:[NSArray arrayWithObjects:@"Title"]];
NSDictionary *item2 = [NSDictionary dictionaryWithObject:[NSArray arrayWithObject:@"Do the training"] forKey:[NSArray arrayWithObjects:@"Title"]];
NSDictionary *item3 = ... 

[root setObject:item1 forKey:@"Item 1"];
[root setObject:item2 forKey:@"Item 2"];

Also did some research and tried something else with some other input..

NSMutableArray *Rows = [NSMutableArray arrayWithCapacity: 1];

for (int i = 0; i < 4; ++i) {
  NSMutableArray *theChildren = [NSMutableArray arrayWithCapacity: 1];
  [theChildren addObject: [NSString stringWithFormat: @"tester %d", i]];
NSString *aTitle = [NSString stringWithFormat: @"Item %d", i];
  NSDictionary *anItem = [NSDictionary dictionaryWithObjectsAndKeys: aTitle, @"Title", theChildren, @"Children"];
  [Rows addObject: anItem];
}

NSDictionary *Root = [NSDictionary withObject: Rows andKey: @"Rows"];

I decided to just test both of these however it does what I want. It gives me a EXC_BAD_ACCESS error.

I was also wondering since I saw you using number in your code snippet, couldn't you also use NSString since that's what the plist uses.. could be totally of here of course

NSDictionary *item1 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"Screen J",[NSNumber numberWithInt:3],nil]
                                                  forKeys:[NSArray arrayWithObjects:@"Title",@"View",nil]];

and third a question is about my possible approach to my app. I have an xml parser which saves certain information in different arrays. I want to use this information for my drilldown UITableviews (infoFirstScreen[] infoSecondScreen[] infoThirdScreen[]). The information provided has to be connected like the tree I showed you above. This is the reason I wanted to build the dictionary in code so I can take the info from my arrays and insert it here. My question do you think my approach is correct, wrong or is there a faster way?

again really appreciate the explanation ;)

Answer 4

I am not sure I understand the basic objective here.

It seems like at runtime, you are constructing a deep dictionary with many child nodes. But you are constructing this all with static code... why can you not simply make a plist (like the one you had an image of) and read that into an NSDictionary? Both NSDictionary and NSArray have methods that let you simply read in a file and get a whole filled out object. Then it is WAY easier to edit and to understand. That method is dictionaryWithContentsOfFile.

If all of the data is truly created at runtime before it is put into the dictionary, then it seems like you would want a very different, recursive, style of code rather than the flat examples given.

Lastly, I personally dislike the dictionaryWithObjects:forKeys: method in NSDictionary for building a dictionary. If you have to do things that way I greatly prefer the alternate method dictionaryWithObjectsAndKeys: which does the same thing but keeps the keys with the objects:

NSDictionary *item1 = [NSDictionary dictionaryWithObjectsAndKeys:
                       @"Screen J",
                       @"Title",
                       [NSNumber numberWithInt:3],
                       @"View"];