Subclassing NSURLConnection gives error: unrecognized selector sent to instance - ios

Question

i'm trying to make a subclass of NSURLConnection where i have an additional property (in this case "connectionName") to help me distinguish between 2 different connections.
i created the subclass, named it CustomURLConnection and gave it the property "connectionName".
then in my file ImagesViewController.m (which is an UICollectionView) i import the header CustomURLConnection and try to give the connections a name and retrieve it afterwards, but it doesn't work, as soon as i enter this collection view the app crashes and gives me the following error:
-[NSURLConnection setConnectionName:]: unrecognized selector sent to instance 0x1090a40f0
Here is some code: (if you want, here's a CLEARER IMAGE)
CustomURLConnection.h
#import <Foundation/Foundation.h>
#interface CustomURLConnection : NSURLConnection
#property (strong, nonatomic) NSString *connectionName;
#end
ImagesViewController.h
#import <UIKit/UIKit.h>
#interface ImagesViewController : UICollectionViewController<NSURLConnectionDelegate>
#property (strong, nonatomic) UIImageView *imageView;
#end
ImagesViewController.m
...
#import "CustomURLConnection.h"
#interface ImagesViewController (){
NSArray *contentStrings;
NSMutableData *contentData; // Holds data from the initial load
NSMutableData *contentImageData; // Holds data when the user scrolls up/down in the collection view
}
#end
...
-(void)loadInitialData{ // Loads data from page
NSString *hostStr = #"http://www.website.com/example";
NSURL *dataURL = [NSURL URLWithString:hostStr];
NSURLRequest *request = [NSURLRequest requestWithURL:dataURL];
CustomURLConnection *connectionData = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection
connectionData.connectionName = #"InitialData"; // Give it a name
}
...
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
// Do some stuff
NSString *hostStr = #"http://www.website.com/example2";
_imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,100,100)];
[imageCell addSubview:_imageView]; // Adds an image view to each collection cell
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:hostStr]];
CustomURLConnection *connectionImg = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection
connectionImg.connectionName = #"ImageData"; // Give it a different name than before
// Do some stuff
return imageCell;
}
...
// Here are the main methods for the connections
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
if([((CustomURLConnection *)connection).connectionName isEqualToString:#"InitialData"]){
contentData = [[NSMutableData alloc] init];
}
else{
contentImageData = [[NSMutableData alloc] init];
}
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
if([((CustomURLConnection *)connection).connectionName isEqualToString:#"InitialData"]){
[contentData appendData:data];
}
else{
[contentImageData appendData:data];
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
if([((CustomURLConnection *)connection).connectionName isEqualToString:#"InitialData"]){
// Do some stuff
}
else{
UIImage *image = [[UIImage alloc] initWithData:contentImageData];
_imageView.image = image;
}
}
am i missing something? i came across this error many times before but the causes are never the same and this time i can't seem to find a solution on my own.
hopefully you can see what i'm doing wrong and help me :)
thanks.
EDIT: turns out there is a better way to achieve my goal, have a look here
Thank again to everyone for the help :)

Answer 1

CustomURLConnection *connectionImg = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection
creates an NSURLConnection object. Casting to CustomURLConnection does not change
the class of this object. Replace that line with
CustomURLConnection *connectionImg = [CustomURLConnection connectionWithRequest:request delegate:self]; // Make connection
to create an instance of your subclass.

Answer 2

In your delegate methods change NSURLConnection by CustomURLConnection, for instance :
- (void)connection:(CustomURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
and when you create it just do :
CustomURLConnection *connectionImg = [[CustomURLConnection alloc] initWithRequest:request delegate:self];
connectionImg.connectionName = #"ImageData"; // Give it a different name than before

Answer 3

In this line:
CustomURLConnection *connectionData = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self];
you are creating an instance of NSURLConnection, not CustomURLConnection. So, when you cast the result to CustomURLConnection * you are lying to the compiler.
Later, at runtime, when you try to use a feature of CustomURLConnection you get an exception because your connection is the wrong class type and doesn't implement the method.
You need to instantiate CustomURLConnection, not NSURLConnection.

Answer 4

Adding to the other good answers here, your CustomURLConnection class should override +connectionWithRequest:delegate: to return an instance of CustomURLConnection, like this:
+(CustomURLConnection*)connectionWithRequest:(NSURLRequest*)request delegate:(id)delegate
{
return [[CustomURLConnection alloc] initWithRequest:request delegate:delegate];
}
That lets you use the same style you had:
CustomURLConnection *connectionData = [CustomURLConnection connectionWithRequest:request delegate:self]; // Make connection
More importantly, a user of your code (most likely the future you) might assume that sending +connectionWithRequest:delegate: to CustomURLConnection would return an instance of CustomURLConnection. Without the override, they'll get an instance of NSURLConnection instead, and that's a difficult bug to spot.