iOS - CLLocationCoordinate2D/floats/long into a NSDictionary for JSON? - objective-c

Question

I'm looking to convert a simple objectiveC class (not even that at the minute its just some vars in a function) to JSON so that it can be sent and impretated into a java object at the server side.
The Class might have the following fields;
LatLng locationA // a simple POJO with either float or long to represent lat and long.
LatLng locationA
float someFloat
It the minute I am tring to pack everything in to a NSDictonary. Passing the floats in didn't work so I has to convert them to NSStrings. So on the server side they would arive as strings.. which isnt ideal.
CLLocationCoordinate2D location = ... ;
float lat = location.latitude;
float lng = location.longitude;
float aFloat = 0.12434f;
NSString *aFloatstr = [NSString stringWithFormat:#"%f", aFloat];
NSString *latStr = [NSString stringWithFormat:#"%f", lat];
NSString *lngStr = [NSString stringWithFormat:#"%f", lng];
NSDictionary *locationDictionary =
[NSDictionary dictionaryWithObjectsAndKeys:
latStr , #"latitude",
lngStr, #"longitude",
nil];
NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
locationDictionary, #"locationA",
locationDictionary, #"locationB",
aFloatstr,#"aFloat",
nil];
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictionary options:NSJSONWritingPrettyPrinted error:&error];
NSString *str = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(#"%#",str);
Whats the best way do putting CLLocationCoordinate2Ds into an NSDictionary?
How do I add primitative types, long floats ect.. to an NSDictionary?

Answer 1

Instead of putting the latitude and longitude into NSString, you'll have better luck with NSNumber. When NSJSONSerialization comes upon an NSNumber it won't quote the value like it would a string (which is what you want when transmitting numbers, right?).
You'll also want to use double, not float, for latitude and longitude, since that's how they're represented internally. No need to throw away precision.
[NSNumber numberWithDouble:lat]
[NSNumber numberWithDouble:lng]
[NSNumber numberWithFloat:aFloat]
Since instances of NSNumber are objects, you'll be able to store them in NSDictionary no problem.

Answer 2

Use NSNumber instead of strings to wrap the float values, e.g.:
NSDictionary *locationDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithFloat:lat] , #"latitude",
[NSNumber numberWithFloat:lng], #"longitude", nil];
That way, NSJSONSerialization will correctly encode them as numeric values.

Answer 3

Structs
Neat way of doing this is to create category for NSValue that understands your struct. In your case it's CLLocationCoordinate2D, but could be any really. Here is snippet from Apple's own documentation explaning usage of NSValue:
// NSValue+Polyhedron.h
typedef struct {
int numFaces;
float radius;
} Polyhedron;
#interface NSValue (Polyhedron)
+ (instancetype)valueWithPolyhedron:(Polyhedron)value;
#property (readonly) Polyhedron polyhedronValue;
#end
// NSValue+Polyhedron.m
#implementation NSValue (Polyhedron)
+ (instancetype)valueWithPolyhedron:(Polyhedron)value
{
return [self valueWithBytes:&value objCType:#encode(Polyhedron)];
}
- (Polyhedron) polyhedronValue
{
Polyhedron value;
[self getValue:&value];
return value;
}
#end
From here usage is quite trivial. To create boxed NSValue:
NSValue *boxedPolyhedron = [NSValue valueWithPolyhedron:yourStruct];
Now you can put boxedPolyhedron whenever NSValue can go, NSArray, NSDictionary, NSSet, and many more, plus al the mutable versions.
To get struct back:
Polyhedron polyStruct = [boxedPolyhedron polyhedronValue];
That's it.
As a bonus, this works for any C type, not only for structs.
floats, longs, etc.
As mentioned above, could do same as above. But, for numbers, you could use NSNumber which is actually a subclass if NSValue with all popular methods already implemented. Here is a list of types you can box by instantiating NSNumber:
+ (NSNumber *)numberWithChar:(char)value;
+ (NSNumber *)numberWithUnsignedChar:(unsigned char)value;
+ (NSNumber *)numberWithShort:(short)value;
+ (NSNumber *)numberWithUnsignedShort:(unsigned short)value;
+ (NSNumber *)numberWithInt:(int)value;
+ (NSNumber *)numberWithUnsignedInt:(unsigned int)value;
+ (NSNumber *)numberWithLong:(long)value;
+ (NSNumber *)numberWithUnsignedLong:(unsigned long)value;
+ (NSNumber *)numberWithLongLong:(long long)value;
+ (NSNumber *)numberWithUnsignedLongLong:(unsigned long long)value;
+ (NSNumber *)numberWithFloat:(float)value;
+ (NSNumber *)numberWithDouble:(double)value;
+ (NSNumber *)numberWithBool:(BOOL)value;
+ (NSNumber *)numberWithInteger:(NSInteger)value;
+ (NSNumber *)numberWithUnsignedInteger:(NSUInteger)value;
In similiar fashion you un-box values using [yourNumber longValue], [yourNumber floatValue], etc.
Hope that helps.