Trying add NSMutableDictionary to NSMutableArray - ios

Question

I am very new to Objective-C and iOS programming so be gentle :)
I am trying to add an nsmutabledictionary to and nsmutablearray. I am succeeding but not with the results I was hoping for. Here is my code :
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
NSMutableDictionary *messages = [[NSMutableDictionary alloc] init];
NSMutableArray *array = [[NSMutableArray alloc] init];
[dictionary setValue:#"lat1" forKey:#"lat"];
[dictionary setValue:#"long1" forKey:#"long"];
[dictionary setValue:#"alt1" forKey:#"alt"];
[messages setObject:dictionary forKey:#"messages"];
[array addObject:messages];
[dictionary setValue:#"lat2" forKey:#"lat"];
[dictionary setValue:#"long2" forKey:#"long"];
[dictionary setValue:#"alt2" forKey:#"alt"];
[messages setObject:dictionary forKey:#"messages"];
[array addObject:messages];
NSLog(#"%#",array);
NSLog(#"%lu",(unsigned long)[array count]);
Here is the NSLog output:
2014-06-05 10:29:27.377 dicttest[4863:60b] (
{
messages = {
alt = alt2;
lat = lat2;
long = long2;
};
},
{
messages = {
alt = alt2;
lat = lat2;
long = long2;
};
}
)
2014-06-05 10:29:27.386 dicttest[4863:60b] 2
Here is what I was hoping to achieve:
2014-06-05 10:29:27.377 dicttest[4863:60b] (
{
messages = {
alt = alt1;
lat = lat1;
long = long1;
};
},
{
messages = {
alt = alt2;
lat = lat2;
long = long2;
};
}
)
2014-06-05 10:29:27.386 dicttest[4863:60b] 2
If I the dictionary straight to the array (instead of add the dictionary to messages and then adding that to the array) then I get the output I am looking for. Can somebody explain to me exactly what I am doing wrong?

Answer 1

It looks to me like you want:
An array
At index 0:
A dictionary with a single key "messages"
A dictionary with keys "alt", "lat", and "long"
At index 1:
A dictionary with a single key "messages"
A dictionary with keys "alt", "lat", and "long"
The data in the second array entry should use the same keys, but different data. As the others have pointed out, your mistake is using a single dictionary "dictionary"
When you add an object to a collection like a dictionary or array, the collection holds a pointer to the object, not a copy of the object. If you add the same object to a collection more than once, you have 2 pointers to the same object, not 2 unique objects.
When you add your "dictionary" object, to your structure, change it, and add it again, you are not getting the result you expect because both entries in your structure point to a single dictionary. When you change the values, it changes in both places.
The same goes for your "messages" dictionary. You need 2 of those as well.
Fix your code by adding new dictionaries, dictionary2 and messages2:
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
NSMutableDictionary *dictionary2 = [[NSMutableDictionary alloc] init];
NSMutableDictionary *messages = [[NSMutableDictionary alloc] init];
NSMutableDictionary *messages2 = [[NSMutableDictionary alloc] init];
NSMutableArray *array = [[NSMutableArray alloc] init];
[dictionary setValue:#"lat1" forKey:#"lat"];
[dictionary setValue:#"long1" forKey:#"long"];
[dictionary setValue:#"alt1" forKey:#"alt"];
[messages setObject:dictionary forKey:#"messages"];
[array addObject:messages];
[dictionary2 setValue:#"lat2" forKey:#"lat"];
[dictionary2 setValue:#"long2" forKey:#"long"];
[dictionary2 setValue:#"alt2" forKey:#"alt"];
[messages2 setObject: dictionary2 forKey:#"messages"];
[array addObject: messages2];
NSLog(#"%#",array);
NSLog(#"%lu",(unsigned long)[array count]);
You might also look at using object literal syntax, e.g.:
dictionary[#"lat"] = #"lat1";
dictionary[#"long"] = #"long1";
dictionary[#"alt"] = #"alt1";
messages[#"messages"] = dictionary;
If you didn't need the whole thing to be mutable, you could even do everything with one line:
NSMutableArray *array = [
#[
#{#"messages": #{#"lat": #"lat1", #"long": #"long1", #"alt": #"alt1"}},
#{#"messages": #{#"lat": #"lat2", #"long": #"long2", #"alt": #"alt2"}}
];
Or to make it mutable:
NSMutableArray *array = [
#[
[#{#"messages":
[#{#"lat": #"lat1", #"long": #"long1", #"alt": #"alt1"} mutableCopy]} mutableCopy],
[#{#"messages":
[#{#"lat": #"lat2", #"long": #"long2", #"alt": #"alt2"} mutableCopy]} mutableCopy]
] mutableCopy];
EDIT: to add contents dynamically, you could use a method like this: (assuming that array is an instance variable)
- (void) addMessageWithLat: (NSString *) latString
long: (NSString *) longString
alt: (NSString *) altString;
{
NSMutableDictionary *messages = [[NSMutableDictionary alloc] init];
NSDictonary *contents =
[#{#"lat": latString,
#"long": longString,
#"alt": altString}
mutableCopy];
messages[#"messages"] = contents;
[array addObject: messages];
}

Answer 2

The problem is that you are making adding the new values in the same object reference. So the new Value will replace the older one. Just add this line before [dictionary setValue:#"lat2" forKey:#"lat"];
dictionary = [NSMutableDictionary alloc]init];
and this line before the second instance of [messages setObject:dictionary forKey:#"messages"];
messages = [[NSMutableDictionary alloc] init];