NSDictionary literals position at run-time

Question

How can I ensure the position of key-value pairs inside a NSDictionary when defining it?

For example if I define:

[detailsView setDatasource: @[ 
   @[@"Details",
      @{ @"title_1":@"description1",
         @"title_2":@"description2",
         @"title_3":@"description3",
         @"title_4":@"description4" }],
   @[@"Actions",
      @{ @"Action_1":[NSNull null],
         @"Action_2":[NSNull null],
         @"Action_3":[NSNumber numberWithBool:false] }]
];

Then at runtime I have different order of items

[detailsView setDatasource: @[ 
   @[@"Details",
      @{ @"title_2":@"description2",
         @"title_3":@"description3",
         @"title_4":@"description4",
         @"title_1":@"description1" }],
   @[@"Actions",
      @{ @"Action_3":[NSNumber numberWithBool:false],
         @"Action_1":[NSNull null],
         @"Action_2":[NSNull null]}]
];

This behaviour is unpredictable... How NSDictionary is initialised when initialising it with literals , and is there a way of ensure that a key-value pair will be at defined position when using literals ?

-- EDIT --

Not a brilliant solution but works. I ended-up doing like this:

@[
    @[ @"Route details",
         @[
              @[@"route-direction", @"Route direction", [NSString stringWithFormat:@"%@ → %@", journey[@"from"], journey[@"to"]]],
              @[@"poi-count", @"Points of interest", journey[@"pois-count"]],
              @[@"date-created", @"Date created", journey[@"created-at"]],
          ]
     ],
    @[ @"Actions" ,
         @[
             @[@"favourite", @"Favourite", ( [journey objectForKey:@"favourite"] ? [journey objectForKey:@"favourite"] : [NSNumber numberWithBool:false])],
             @[@"load",@"Load now",[NSNull null]],
             @[@"delete",@"Delete",[NSNull null]],
          ]
     ],
[NSNumber numberWithInteger: indexPath.row]]];

you question make no point as long as you will access to the _values_ by the _keys_ only (`–valueForKey:` or `–valueForKeyPath:`), so the actual order of the elements are really irrelevant. what do you like to achieve anyway? — holex, Nov 04 '14 at 11:11
I wanted to have a ViewController that displays properties and actions, different for different selected item, in different tableViews. I setup properties and values, then actions available for that items with selector names. And for actions i may need to display the "Delete" action after all actions. — Svenv, Nov 12 '14 at 14:56

score 0 · Accepted Answer · answered Nov 04 '14 at 09:15

0

NSDictionary is not a ordered container.If you use it,you should not care the order of data.

If you want a ordered dictionary,refer to this link

http://www.cocoawithlove.com/2008/12/ordereddictionary-subclassing-cocoa.html

Or you may write another NSArray/NSMutableArray to keep the keys order of this NSDictionary.

Or just use NSArray instead of NSDictionary,one array keep keys,another array keep values

Hope this could be helpful

answered Nov 04 '14 at 09:15

Leo

24,596
11
71
92

Thanks, that was useful ... I decided to use 2 dimensional NSArray instead of NSDictionary. This way I am solved the problem of having an "action-name", "action title", "action value". – Svenv Nov 04 '14 at 09:44
@slava At the expense of look-up speed. – trojanfoe Nov 04 '14 at 09:57
@trojanfoe Possible, but I am using only 6 items. I know that is not an excuse for writing inefficient code but... what else can I do, use plain C arrays ? how? I am trying to set data source for a ViewController with table that displays property-value list and actions ( for selected item ) – Svenv Nov 04 '14 at 10:27
@slava You use both. A dictionary to hold key/values of the actual data and an array of the keys to hold the order you want that data to appear in, allowing re-ordering etc. – trojanfoe Nov 04 '14 at 11:18

NSDictionary literals position at run-time

1 Answers1