Does a NSURLConnection retain its delegate?


Does a NSURLConnection retain its delegate?



Summary of my question: Does NSURLConnection retain its delegate?

Detailed question and scenario:

I have a custom class, called JsonDownloader that is takes in a URL and returns an NSDictionary of the JSON that the URL returns.

On an iPhone app, I do something like this. (the init method kicks off the whole process)

- (void)viewDidLoad {     JsonDownloder *temp = [[[JsonDownloader alloc] initWithURL:urlString returnDataTo:self]];     [temp release];     [super viewDidLoad]; } 

When the JsonDownloader is done downloading and parsing, it performs a callback to the returnDataTo: object, in this case, the calling object.

This works just fine. Even if I introduce a 30 second delay in my web servers response, the JsonDownloader still exists and does it's callback correctly.

So my questions is this: What is keeping JsonDownloader way past the end of the event cycle? I am explicitly releasing it.

My hunch is that NSURLConnection must do a retain on its delegate, but I didn't see anything in the documentation. Anyone have an ideas?




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1:



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There aren't many setters that don't either copy or retain a variable being passed to it, lest the memory of said variable be re-allocated to something else when its retain count reaches zero..
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However, the answer is YES, it does.


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A little bit of test code shows the delegate's retain count go up:.
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NSLog(@"Retain count before: %d", [self retainCount]); NSURLRequest* request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]]; NSURLConnection* conn = [NSURLConnection connectionWithRequest:request delegate:self]; NSLog(@"Retain count after: %d", [self retainCount]); 
which produces in the log:.
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Running… 2009-07-09 02:13:40.516 delegateRetain[45123:a0f] Retain count before: 1 2009-07-09 02:13:40.525 delegateRetain[45123:a0f] Retain count after: 2  Debugger stopped. 


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So you can see pretty clearly that in connectionWithRequest:delegate: "self" is indeed having its retain count increased +1.


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If you're feeling brave and want to mess with the EXC_BAD_ACCESS gods, add in.
[conn dealloc]; NSLog(@"Retain count after dealloc: %d", [self retainCount]); 
which will print out "1" again, showing a post dealloc decrement.

However, you'll get a nice Program received signal: “EXC_BAD_ACCESS”. because the NSAutoreleasePool will try to release the connection and it will be gone ;).


2:


Most delegate properties are not retained but assigned to prevent circular references.

See this question about that as well.. However, NSUrlConnection does not have a specific delegate property.

You have to specify the delegate along with the initialization of the connection.

I think that is why it does receive a retain, as Dave Martorana showed..


3:


Yes, "The connection retains delegate.

It releases delegate when the connection finishes loading, fails, or is canceled," according to the Xcode Documentation for -[NSURLConnection initWithRequest:delegate:] under Special Considerations.

See also: NSURLConnection inherent memory leak?.



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