NSURL property 'absoluteURL' - ios

Question

I'm developing my own app, the iPhone version of this App is already on the Apple AppStore and now I'm working on the iPad version. Functionalities are (of course) nearly the same, but the user interface is different. The iPhone version is working fine.
Now I'm getting a strange error in XCode.
My app uses the SoundCloud API to stream some music and browse the songs of different users. On an iPhone I can display the small thumbnail images, because the ImageViews are pretty small (~40x40px).
But on my iPad, I need the bigger images, so I have to fetch the bigger artwork images and user avatars.
For that, I have two different methods. The first one fetches the bigger Artwork Image, the second one the bigger user avatar (profile picture).
- (NSURL *)bigCoverURLforTrack:(Track *)track {
if(track.coverURL) {
NSURL* coverURL = track.coverURL;
NSString* coverLarge = coverURL.absoluteString;
NSString* coverBig = [coverLarge stringByReplacingOccurrencesOfString:#"-large" withString:#"-t500x500"];
return [[NSURL alloc] initWithString:coverBig];
}
else return [[NSURL alloc] init];
}
- (NSURL*)bigAvatarURLforUser:(User*)user {
if(user.avatarURL) {
NSURL* avatarURL = user.avatarURL;
NSString* avatarLarge = avatarURL.absoluteString;
NSString* avatarBig = [avatarLarge stringByReplacingOccurrencesOfString:#"-large" withString:#"-t500x500"];
return [[NSURL alloc] initWithString:avatarBig];
}
else return [[NSURL alloc] init];
}
The first method is working fine, but the second one crashes each time.
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString absoluteString]: unrecognized selector sent to instance
What am I doing wrong?

Answer 1

It must be that this line:
NSURL* avatarURL = user.avatarURL;
Is setting avatarURL to a string rather than an NSURL. Fix that at the source (make sure the method on user answers a real NSURL, not NSString), or force the type when you get it like this:
NSURL* avatarURL = [NSURL URLWithString:user.avatarURL];