Question

I have an odd problem that is crashing my app, that I would like some opinions on if possible.

I have an NSURLConnection, submitting POST data to an external PHP file and getting a response back that is displayed on the iPhone.

This all works fine, and can be done many times without error, without any leaks showing up in analysis and without any crashes.

The app also has an “email the response” option, and if this is pressed, the email program opens up, and that all works fine without issue as well.

However, on closing the email program and returning back to the main app again, if the “fetch data” button is now pressed, and the NSURLConnection done again, the app immediately crashes.

I can’t test this on the simulator, as it doesn’t open up the email program on the simulator – this is on real testing only on an iPhone. All tests and analysis done on within Xcode shows up fine and doesnt point to any issues.

All my code for the NSURLConnection to POST and retrieve the data is as follows:

- (void)FetchData {
result.text = @"";
emailbutton.hidden = YES;
emailbutton.enabled = NO;

NSString *queryStringFull = [queryStringFirst stringByAppendingString:textField.text];

NSURL *url = [NSURL URLWithString:@"http://www.mydomain.com/mypage.php"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
NSData *requestData = [queryStringFull dataUsingEncoding:NSUTF8StringEncoding];

[request setHTTPMethod:@"POST"];
[request setValue:@"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8" forHTTPHeaderField:@"Accept"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setValue:[NSString stringWithFormat:@"%d", [requestData length]] forHTTPHeaderField:@"Content-Length"];
[request setHTTPBody: requestData];
[NSURLConnection connectionWithRequest:(request) delegate:self];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
responseData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[responseData appendData:data];
}

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

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSString* responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
if (![responseString isEqualToString:@"error"]) {
    result.text = responseString;
    emailbutton.hidden = NO;
    emailbutton.enabled = YES;
}
[responseString release];
[responseData release];
}

I would be very grateful for any ideas or thoughts on what is causing this, and how to solve it.

Answer 1

Actually, it wasn’t the NSURLConnection at all!

Turns out it was an image call that happens after the NSURLConnection call. The image was defined in viewdidload, released, and then was not defined after the app came back from the background.

Adding a “retain” to the image definition in the viewdidload solved the issue!