It expects an NSURL as argument, not a string.
UIImage *image = [UIImage imageWithData: [NSData dataWithContentsOfURL: [NSURL URLWithString:@"http://ws.cdyne.com/WeatherWS/Images/thunderstorms.gif"]]];
EDIT:
To test if the data has loaded succesfully try something like
NSError* error = nil;
NSData* data = [NSData dataWithContentsOfURL:yourURL options:NSDataReadingUncached error:&error];
if (error) {
NSLog(@"%@", [error localizedDescription]);
[error release];
} else {
NSLog(@"Data has loaded successfully.");
}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…