CODEWITHSUNDEEP
iosobjective-c
Evgeniy Kleban
Evgeniy Kleban

Reputation: 6940

NSDictionary syntax explanation

I have UITableView and NSDictionary. It populated like follow:

    currentAlbumData = [album tr_tableRepresentation];

Where albums is simple NSObject class:

// h.file
@interface Album : NSObject

@property (nonatomic, copy, readonly) NSString *title, *artist, *genre, *coverUrl, *year;

-(id)initWithTitle:(NSString*)title artist:(NSString*)artist coverUrl:(NSString*)coverUrl year:(NSString*)year;

//m.file

-(id)initWithTitle:(NSString *)title artist:(NSString *)artist coverUrl:(NSString *)coverUrl year:(NSString *)year{

self = [super init];
if (self){

    _title = title;
    _artist = artist;
    _coverUrl = coverUrl;
    _year = year;
    _genre = @"Pop";
}
return self;

};

And tr_tableRepresentation is category of Album class, returning NSDictionary:

//h.file

@interface Album (TableRepresentation)

- (NSDictionary*)tr_tableRepresentation;

@implementation Album (TableRepresentation)

//.m file

- (NSDictionary*)tr_tableRepresentation
{
    return @{@"titles":@[@"Artist", @"Album", @"Genre", @"Year"],
             @"values":@[self.artist, self.title, self.genre, self.year]};
}

That is the code i take from tutorial, so, in following lines we populate tableView data with NSDictionary values:

-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];

    //... Cell initialization code

    cell.textLabel.text = currentAlbumData[@"titles"][indexPath.row];
    cell.detailTextLabel.text = currentAlbumData[@"values"][indexPath.row];
}

Now I'm stuck. because I'm getting confused when i see syntax like that. 

cell.textLabel.text = currentAlbumData[@"titles"][indexPath.row];
        cell.detailTextLabel.text = currentAlbumData[@"values"][indexPath.row];

What exactly is going on here? What this lines of code do? I can understand that we accessing @"titles" and @"values" somehow, could you please rewrite that lines in more readable manner, without square brackets?

And how could we even get @"titles" and @"values" using just indexPath (integer number)? That may sound kind of silly, but I'm not get it. I thought we have to put string as a parameter to access NSDictionary values, not an integer.

Upvotes: 0

Views: 158

Answers (3)

user3575114
user3575114

Reputation: 993

Titles is an array so to get value at particular index you can use

cell.textlabel.text = [[currentAlbumData valueForKey:@"titles"] objectAtIndex:indexPath.row];

If you find this confusing then better store Titles inside an array and then use it below

NSArray *titles = [currentAlbumData valueForKey:@"titles"];
cell.textlabel.text = [titles objectAtIndex:indexPath.row];

Upvotes: 1

stevesliva
stevesliva

Reputation: 5655

titles is the key for an NSArray of NSStrings. So is values.

currentAlbumData[@"titles"] asks the dictionary for the value at the titles keypath. This returns an NSArray that is indexed by NSUIntegers, such as indexPath.row.

Upvotes: 1

Schrodingrrr
Schrodingrrr

Reputation: 4271

It is just a short way of writing code:

currentAlbumData[@"titles"][indexPath.row] is same as [[currentAlbumData objectForKey:@"titles"] objectAtIndex:indexPath.row]. Here, currentAlbumData is a dictionary. You get it's object for key titles, which is (supposedly) an array. Then you get the object at index indexPath.row of this array.

Upvotes: 1

Related Questions