How do you verify that NSURLConnection was successful - objective-c

Question

[NSURLConnection sendAsynchronousRequest:mutURLRequest queue:opQueue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
if(httpResponse.statusCode ==200)
{
[[NSNotificationCenter defaultCenter] postNotificationName:#"MUITCheckinPostSucceeded" object:self userInfo:postDictionary];
}
}];
This is my NSURLConnection and I'm not sure how to check if it was successful. I tried a simple flag but that did not work because the boolean didn't retain the "YES" value outside of the NSURLConnection. This is a school assignment so don't post the correct code I'd just like to know the method I need to implement or how I can tackle this problem in a way I haven't tried yet. Thanks in advance.

Answer 1

Try something like this:
[NSURLConnection sendAsynchronousRequest: myURLRequest
queue: [NSOperationQueue mainQueue]
completionHandler: ^(NSURLResponse *urlResponse, NSData *responseData, NSError *requestError) {
// Check for Errors
if (requestError || !responseData) {
// jump back to the main thread to update the UI
dispatch_async(dispatch_get_main_queue(), ^{
[myLabel setText: #"Something went wrong..."];
});
} else {
// jump back to the main thread to update the UI
dispatch_async(dispatch_get_main_queue(), ^{
[myLabel setText: #"All going well..."];
});
}
}
];

Answer 2

You can update your class properties from the completion block. In this case, if flag was atomic, you can just update it. But if you're setting anything else (e.g. any object properties updated from the resulting data object), you might want to dispatch that back to the main queue to avoid synchronization issues:
self.flag = NO;
[NSURLConnection sendAsynchronousRequest:mutURLRequest queue:opQueue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSInteger statusCode = -1;
// to be safe, you should make sure `response` is `NSHTTPURLResponse`
if ([response isKindOfClass:[NSHTTPURLResponse class]])
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
statusCode = httpResponse.statusCode;
}
if (error)
{
// for diagnostic purposes only
NSLog(#"%s: sendAsynchronousRequest error: %#", __FUNCTION__, error);
}
if (error == nil && statusCode == 200)
{
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
self.flag = YES;
// set any other class properties here
[[NSNotificationCenter defaultCenter] postNotificationName:#"MUITCheckinPostSucceeded" object:self userInfo:postDictionary];
}];
}
}];
I notice that you're posting a notification. If you have multiple view controllers or model objects listening for that notification, that's fine and a notification makes sense. But if this code was in the view controller and that controller is the only thing that cares about the results, you generally forego the notification and just initiate the update the UI right from the code that's dispatched back to the main queue in that completion block.
One final caveat. Any references to self (or ivars, which have an implicit reference to self) will maintain a strong reference to the object for the duration of the operation (i.e. it will retain it). For example, if you dismiss the view controller while the network operation is in progress, the view controller won't be released until after the network operation is done. That's often fine (as it's just for the duration of the connection ... it's not the dreaded strong reference cycle), especially for a school assignment. But if that's an issue, there are techniques to only use a weak reference to the view controller inside the completion block, thus preventing the retaining of the view controller for the duration of the network operation. But that's beyond the scope of your original question (esp since it leads to a bunch of other questions about whether you want to cancel the network operation or not, when you dismiss the view controller), so I'll leave it at here.