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iOS Objective-C Basics (Retired) Foundation Framework NSDictionary

NSMutableDictionary. Adding a value and key problems...

Im a little bit confused why the instructions say to add a NSString when I thought I should be adding [mutableAlbum setObject:@1969 forKey:@"year"];

So here is what I have:

NSDictionary *album = @{ @"title":@"Abbey Road", @"artist":@"The Beatles" }; NSMutableDictionary *albumMutable = [NSMutableDictionary dictionaryWithDictionary:album]; NSString *year =[albumMutable objectForKey:@"1969”]; or [albumMutable setObject:@1969 forKey:@"year”];

I know both of the last lines are incorrect but would like someone to explain to me why. Thanks in advance!


1 Answer

Ben Falk
Ben Falk
3,167 Points

This is the question: Let's add the year of the album to the 'albumMutable' variable. Where the key is a NSString 'year' and the value is also a NSString '1969'.

I don't really think there is a specific reason why an NSString is asked for, other than perhaps to make sure you are actually understanding the information, and not blindly copying from the video. I agree that an NSNumber, like "@1969" probably makes more sense.

NSString *year =[albumMutable objectForKey:@"1969”]; This doesn't work because it isn't what the question is asking for. Instead of adding an item to the albumMutable variable, this line creates a new NSString, which tries to access the album information and retrieve the value for key "1969". You're retrieving info rather than setting it.

[albumMutable setObject:@1969 forKey:@"year”]; This doesn't work because while you are setting an object, the question is expecting the value for "year" to be a string, whereas the code here sets it to an NSNumber. Since the question asks for the value to be a string, you'll need to surround the year with quotation marks in order for it to work.