Get values from NSDictionaries - ios

Question

I have the following code:
NSDictionary *dict = #[#{#"Country" : #"Afghanistan", #"Capital" : #"Kabul"},
#{#"Country" : #"Albania", #"Capital" : #"Tirana"}];
I want to list many countries and capitals, and then randomize i.e a country and put it on the screen, then the user should be able to pick the correct capital..
How to I put the Country? Like dict.Country[0] or something like that?
What is wrong with the code? I get the error "Initializer element is not a compile-time constant" and the warning "Incompatible pointer types initializing 'NSDictionary *_strong' with an expression of type 'NSArray *'.
Can I make a third String in the Dictionary, containing a flag file.. for example
#"Flagfile" : #"Albania.png"
and later put it in a image view?
I want like a loop with a random number I (for example) and put like (I know this is not right, but I hope you get the point)
loop..
....
text= dict.Country[I];
button.text= dict.Capital[I];
Imageview=dict.Flagfile[I];
.....
....

Answer 1

Your top level element is an NSArray (#[], with square brackets, makes an array) of two NSDictionary's. To access an attribute in one of the dictionaries, you would do array[index][key], e.g. array[0][#"Country"] would give you #"Afghanistan". If you did NSArray *array = ... instead of NSDictionary *dict = ...
If you want to pick a country at random, you can get a random number, get it mod 2 (someInteger % 2) and use that as your index, e.g. array[randomNumber % 2][#"Country"] will give you a random country name from your array of dictionaries.
If you store an image name in the dictionaries, you can load an image of that name using UIImage's +imageNamed: method.

Answer 2

Here's more complete instruction on mbuc91's correct idea.
1) create a country
// Country.h
#interface Country : NSObject
#property(strong,nonatomic) NSString *name;
#property(strong,nonatomic) NSString *capital;
#property(strong,nonatomic) NSString *flagUrl;
#property(strong,nonatomic) UIImage *flag;
// this is the only interesting part of this class, so try it out...
// asynchronously fetch the flag from a web url. the url must point to an image
- (void)flagWithCompletion:(void (^)(UIImage *))completion;
#end
// Country.m
#import "Country.h"
#implementation Country
- (id)initWithName:(NSString *)name capital:(NSString *)capital flagUrl:(NSString *)flagUrl {
self = [self init];
if (self) {
_name = name;
_capital = capital;
_flagUrl = flagUrl;
}
return self;
}
- (void)flagWithCompletion:(void (^)(UIImage *))completion {
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:self.flagUrl]];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if (data) {
UIImage *image = [UIImage imageWithData:data];
completion(image);
} else {
completion(nil);
}
}];
}
#end
2) Now, in some other class, use the Country
#import "Country.h"
- (NSArray *)countries {
NSMutableArray *answer = [NSMutableArray array];
[answer addObject:[[Country alloc]
initWithName:#"Afghanistan" capital:#"Kabul" flagUrl:#"http://www.flags.com/afgan.jpg"]];
[answer addObject:[[Country alloc]
initWithName:#"Albania" capital:#"Tirana" flagUrl:#"http://www.flags.com/albania.jpg"]];
return [NSArray arrayWithArray:answer];
}
- (id)randomElementIn:(NSArray *)array {
NSUInteger index = arc4random() % array.count;
return [array objectAtIndex:index];
}
-(void)someMethod {
NSArray *countries = [self countries];
Country *randomCountry = [self randomElementIn:countries];
[randomCountry flagWithCompletion:^(UIImage *flagImage) {
// update UI, like this ...
// self.flagImageView.image = flagImage;
}];
}

Answer 3

You cannot initialize an NSDictionary in that way. An NSDictionary is an unsorted set of key-object pairs - its order is not static, and so you cannot address it as you would an array. In your case, you probably want an NSMutableDictionary since you will be modifying its contents (see Apple's NSMutableDictionary Class Reference for more info).
You could implement your code in a few ways. Using NSDictionaries you would do something similar to the following:
NSMutableDictionary *dict = [[NSMutableDictionary alloc]
initWithObjectsAndKeys:#"Afghanistan", #"Country",
#"Kabul", #"Capital", nil];
You would then have an array of dictionaries, with each dictionary holding the details of one country.
Another option would be to create a simple model class for each country and have an array of those. For example, you could create a Class named Country, with Country.h as:
#import <Foundation/Foundation.h>
#interface Country : NSObject
#property (nonatomic, retain) NSString *Name;
#property (nonatomic, retain) NSString *Capital;
//etc...
#end