Trying to iterate through an Array by checking against keys and objects of an NSDictionary in iOS

Question

I have an NSArray of UISwitches. I have separately an NSDictionary whose keys are NSNumbers, and whose objects are BOOL values in the form of NSString objects. What I would like to do is iterate through the NSArray of UISwitches, check to see if the tag value is one of the keys inside the NSDictionary, and if a match is found, then set the enabled property of the UISwitch to the key's corresponding object (after converting it to a BOOL from an NSString).

My code is as follows:

for (int i=0; i<[self.switchCollection count]; i++) {
     UISwitch *mySwitch = (UISwitch *)[self.switchCollection objectAtIndex:i];
     if (tireSwitch.tag == //this has to match the key at index i) {
                    BOOL enabledValue = [[self.myDictionary objectForKey:[NSNumber numberWithInt://this is the key that is pulled from the line above]] boolValue];
                    mySwitch.enabled = enabledValue;
     }
 }

I don't know how to get the key from the dictionary that corresponds to the index i inside my for loop. — syedfa, Jan 24 '14 at 19:53
Huh? Your code already does that: `[self.myDictionary objectForKey:[NSNumber numberWithInt:i]]` — jscs, Jan 24 '14 at 19:54
That retrieves the object that corresponds to the key. I need the key itself (which is different from the index i). I then need to use the key that I get, to then retrieve the correct object. — syedfa, Jan 24 '14 at 19:57
The key is something other than `[NSNumber numberWithInt:i]`? What is it? How did you build the dictionary in the first place? — jscs, Jan 24 '14 at 19:58
It is composed of two arrays. One for keys, which are NSNumbers, and the objects are NSStrings. — syedfa, Jan 24 '14 at 19:58
Give us an example of what's inside the dictionary, what's inside the array, and what "connection" you want between them — Larme, Jan 24 '14 at 20:00

jscs · Answer 1 · 2014-01-24T20:14:22.217

2

Now that Duncan C's answer has made clear what you're trying to accomplish, it can be written much more simply.

Iterate the array directly. You don't need i at all, since you're not using it to access anything other than the array.

For each switch, try to get a value from the dictionary using the tag (this is wrapped in an NSNumber using the @() boxing syntax.

If a value exists, then set the switch's enabled.

for( UISwitch * switch in self.switchCollection ){
    NSString * enabledVal = self.myDictionary[@(switch.tag)];
    if( enabledVal ){
        switch.enabled = [enabledVal boolValue];
    }
}

edited Jan 24 '14 at 20:14

answered Jan 24 '14 at 20:09

jscs

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1

Josh, while your code is more compact, I think it's better to be verbose in forum posts, from a pedagogical point of view. – Duncan C Jan 24 '14 at 21:34
1

I'd rather describe in English what the idiomatic code does, @DuncanC, so that the goals of understanding and good practice are both served. Fortunately, we can both have it our own way! My answer was not intended as a criticism of yours. :) – jscs Jan 24 '14 at 21:38
1

@JoshCaswell, true enough. We're both trying to help. (+1) – Duncan C Jan 25 '14 at 16:45
Can either of you (Josh or Duncan) suggest a good book on advanced Objective-C programming? I honestly am impressed with the proficiency that both of you have demonstrated here. Thanks again for taking the time to provide a solution for me here. – syedfa Jan 28 '14 at 15:23
1

There aren't really "advanced ObjC books", @syedfa, I'm afraid. You've just got to do it. However, there's a few "recipes" books around, and one called (IIRC) "Cocoa Design Patterns". Big Nerd Ranch has an "Advanced OS X Programming" book (and all their stuff is excellent), but it's about system features, not ObjC. – jscs Feb 02 '14 at 07:13

score 1 · Accepted Answer · answered Jan 24 '14 at 20:00

Your code doesn't look right. How about this:

(Edited to use fast enumeration (for...in loop syntax)

//Loop through the array of switches.
for (UISwitch *mySwitch  in self.switchCollection) 
{
     //Get the tag for this switch
  int tag = mySwitch.tag;

  //Try to fetch a string from the dictionary using the tag as a key
  NSNumber *key = @(tag);
  NSString *dictionaryValue = self.myDictionary[key];

  //If there is an entry in the dictionary for this tag, set the switch value.
  if (dictionaryValue != nil) 
  {
    BOOL enabledValue = [dictionaryValue boolValue];
    mySwitch.enabled = enabledValue;
  }
}

That's assuming I understand what you're trying to do...

Thanks to both Duncan C and Josh. I am humbled by your knowledge. — syedfa, Jan 24 '14 at 20:05

Trying to iterate through an Array by checking against keys and objects of an NSDictionary in iOS

2 Answers2