NSURLConnection with ARC not receiving Data - ios

Question

I'm fairly new to iOS Development and I'm trying to get content from an URL. I'm using the Apple tutorial for using NSURLConnection, everything is working but I'm not getting data. I've looked around and couldn't find an answer to my problem. I'm also using ARC in my project, maybe that causes the problem?
Here is the code I'm using, starting with my header file:
#interface ViewController : UIViewController
#property (nonatomic, retain) NSMutableData *receivedData;
#end
implementation file:
#implementation ViewController
#synthesize receivedData;
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"1. viewDidLoad");
// Create the request
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.apple.com/"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
// Create the connection with the request and start loading the data
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
if (connection) {
NSLog(#"2. connection succeeded");
receivedData = [NSMutableData data];
} else {
NSLog(#"2. connection failed");
}
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
NSLog(#"3. didReceiveResponse");
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(#"4. Connection failed! Error - %# %#", [error localizedDescription], [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(#"4. Succeeded! Received %d bytes of data", [receivedData length]);
}
All the NSLog are working, but it keeps saying receivedData has 0 bytes. I couldn't find an answer to my problem so I hope I can find my answer with this question.

Answer 1

I have translated the Using NSURLConnection part of the URL Loading System Programming Guide using ARC.
//
// MyConnection.h
//
#import <Foundation/Foundation.h>
#interface MyConnection : NSObject
- (void)start;
#property NSMutableData *receivedData;
#end
//
// MyConnection.m
//
#import "MyConnection.h"
#implementation MyConnection
- (void)start {
// Create the request
NSURLRequest *theRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.apple.com"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
// Create the connection with the request and start loading the data
NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMUtableData to fold the received data
// ReceivedData is an instance variable declared elsewhere
_receivedData = [NSMutableData data];
}
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[_receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[_receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
// Inform the user
NSLog(#"Connectionfailed! Error - %# %#",
[error localizedDescription],
[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
// Do something with the data
NSLog(#"Succeeded! Recevied %d bytes of data", [_receivedData length]);
}
#end

Answer 2

Just for the sake of completion. I've had the same problem, with cause in threading. If the thread that owns the NSURLConnection object is different than the thread that owns the delegate, the delegate will not receive notifications. That means that the error in connection would also be gone.
So make sure you create NSURLConnection on same thread that you created the delegate.

Answer 3

You need to start the connection.
You could, for example, use – initWithRequest:delegate:startImmediately:.
An even smaller change to your existing code would be to just use - start on your connection on the if branch:
NSURLConnection *connection = [[NSURLConnection alloc]
initWithRequest:request
delegate:self
startImmediately:NO
];
if (connection) {
NSLog(#"2. connection succeeded");
receivedData = [NSMutableData data];
[connection start];
} else {
NSLog(#"2. connection failed");
}
You can find the reference manual for NSURLConnection here