NSInvalidArgumentException NSDictionary count - iphone

Question

i have write a NSDictionary Category. The Category has a method calls "initWithJSONURL".
Here the code:
- (id)initWithJSONURL:(NSURL *)url
{
self = [super init];
if (self) {
NSError *error;
NSData *data = [NSData dataWithContentsOfURL:url
options:NSUTF8StringEncoding
error:&error];
if (!data) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"connection failed"
message:[error localizedDescription]
delegate:self
cancelButtonTitle:#"cancel"
otherButtonTitles:nil];
[alert show];
} else {
self = [NSJSONSerialization JSONObjectWithData:data
options:0
error:&error];
if (error) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"invalid data"
message:[error localizedDescription]
delegate:self
cancelButtonTitle:#"cancel"
otherButtonTitles:nil];
[alert show];
}
}
}
return self;
}
And here the code from my ViewController viewDidLoad
NSURL *url = [NSURL URLWithString:#"http://localhost:8888/json.php"];
NSDictionary *dict = [[NSDictionary alloc] initWithJSONURL:url];
NSLog(#"%#", dict);
If I use an correct URL everything works perfect.
But if the URL not correct, the App crash.
I don't know why, it should not crash, it should show the alert View.
The consoles show:
erminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSDictionary count]: method sent to an uninitialized immutable dictionary object'
I hope anybody can help me and sorry for my bad english.

Answer 1

You want to call [self init] instead of [super init]. A category is not a subclass, so [super init] means [NSObject init]. The designated initializer of NSDictionary is never called and the internal dictionary structures are staying unitiliazed.