Ios – When does NSURLConnection’s initWithRequest return nil

iosiphonensurlconnectionnull

Does anyone know in which situations initializing a NSURLConnection returns nil instead of the created connection. The documentation says it's possible but fails to specify when this happens.

The method/message in question:

[[NSURLConnection alloc] initWithRequest:request delegate:self];

–

According to the NSURLConnection Class Reference:

Return Value: The URL connection for the URL request. Returns nil if a connection can't be initialized.

The URL Loading System Programming Guide says the following:

If NSURLConnection can’t create a connection for the request, initWithRequest:delegate: returns nil.

–

While it's possible that this method returns nil, I'm unable to come up with a scenario which triggers this. I've tried the following scenarios:

URLRequest with an empty url: connection:didFailWithError: delegate method is called with "unsupported URL" as error.
URLRequest with invalid url: connection:didFailWithError: delegate method is called with "bad URL" as error.
URLRequest with nonexistent url: connection:didFailWithError: delegate method is called with "A server with the specified hostname could not be found." as error.
Valid request but no internet: connection:didFailWithError: delegate method is called with "The Internet connection appears to be offline." as error.
nil request: causes a crash.

The initWithRequest method returned a valid NSURLConnection in each scenario (besides the last one) and called the connection:didFailWithError: with an appropriate error.

Has anybody been able to figure out which scenario does cause nil to be returned?

Best Answer

I believe this can also be used when it fails to load, not just initialize. (The alloc is done separately - that's where low mem would probably bite you) So (I'm guessing) it could fail because you did not have a network available (3G/Wifi) or it simply failed to connect to the server. In any event, use:

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error

To get the actual failure.

You may be able to simulate this with an absence of a network - or even giving it a bad URL.

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Iphone – NSURLConnection delegate methods are not called

Try running the operation on main thread:

NSURLConnection * connection = [[NSURLConnection alloc] 
                                initWithRequest:request
                                       delegate:self startImmediately:NO];

[connection scheduleInRunLoop:[NSRunLoop mainRunLoop] 
                      forMode:NSDefaultRunLoopMode];
[connection start];

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