Cannot get Length of a NSString - unrecognized selector sent to instance - objective-c

Question

What I'm trying to get is to search for the Anime Titile's ID, compare the length and perform some action afterwards. Here is what I get in the debugger:
2010-08-09 14:30:48.818 MAL Updater OS X[37415:a0f] Detected : Amagami SS - 06
2010-08-09 14:30:48.821 MAL Updater OS X[37415:a0f] http://mal-api.com/anime/search?q=Amagami%20SS
2010-08-09 14:30:49.635 MAL Updater OS X[37415:a0f] 8676
2010-08-09 14:30:49.636 MAL Updater OS X[37415:a0f] -[NSCFNumber length]: unrecognized selector sent to instance 0x384aa40
2010-08-09 14:30:49.637 MAL Updater OS X[37415:a0f] -[NSCFNumber length]: unrecognized selector sent to instance 0x384aa40
The code in question:
if ([self detectmedia] == 1) { // Detects Media from MPlayer via LSOF
NSLog(#"Detected : %# - %#", DetectedTitle, DetectedEpisode);
NSString * AniID = [self searchanime]; // Perform a Search Operation and Returns the ID of the time from JSON
NSLog(#"%#",AniID);
if (AniID.length > 0) { // Compare the length of AniID to make sure it contains a ID
// Other Action here
}
//Release Detected Title and Episode
[DetectedTitle release];
[DetectedEpisode release];
}
SearchAnime method:
-(NSString *)searchanime{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
//Escape Search Term
NSString * searchterm = (NSString *)CFURLCreateStringByAddingPercentEscapes(
NULL,
(CFStringRef)DetectedTitle,
NULL,
(CFStringRef)#"!*'();:#&=+$,/?%#[]",
kCFStringEncodingUTF8 );
//Set Search API
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"http://mal-api.com/anime/search?q=%#",searchterm]];
NSLog(#"%#",[NSString stringWithFormat:#"http://mal-api.com/anime/search?q=%#",searchterm]);
//Release searchterm
[searchterm release];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
//Ignore Cookies
[request setUseCookiePersistence:NO];
//Set Token
[request addRequestHeader:#"Authorization" value:[NSString stringWithFormat:#"Basic %#",[defaults objectForKey:#"Base64Token"]]];
//Perform Search
[request startSynchronous];
// Get Status Code
int statusCode = [request responseStatusCode];
NSString *response = [request responseString];
if (statusCode == 200 ) {
return [self RegExSearchTitle:response]; // Returns ID as NSString
}
else {
return #"";
}
}
RegExSearchTitle
-(NSString *)RegExSearchTitle:(NSString *)ResponseData {
OGRegularExpressionMatch *match;
OGRegularExpression *regex;
//Set Detected Anime Title
regex = [OGRegularExpression regularExpressionWithString:DetectedTitle];
NSEnumerator *enumerator;
// Initalize JSON parser
SBJsonParser *parser = [[SBJsonParser alloc] init];
NSArray *searchdata = [parser objectWithString:ResponseData error:nil];
for (id obj in searchdata) {
// Look in every RegEx Entry until the extact title is found.
enumerator = [regex matchEnumeratorInString:[obj objectForKey:#"title"]];
while ((match = [enumerator nextObject]) != nil) {
// Return the AniID for the matched title
return [obj objectForKey:#"id"];
}
}
// Nothing Found, return nothing
return #"";
}
This behavior is unusual because I have compared the NSString's length in the past and it never failed on me. I am wondering, what is causing the problem?

Answer 1

The declared return type of RegExSearchTitle is NSString *, but that doesn’t force the returned object to actually be an NSString. The "id" element of obj (from the JSON) is a number, so an NSNumber is being returned. The compiler can’t warn you about this because it doesn’t know what classes will be found in a collection.
There are other bugs in the code. Having an unconditional return in a while statement in a for statement does not make sense.
On a side note, by convention Objective-C method names start with a lowercase letter.

Answer 2

Well, it's because you assigned an NSNumber to AniID, not an NSString. NSNumber doesn't have a length method.