iPhone app crashes randomly with exc_bad_access - iphone

Question

I have an app with four tabs. In each tab I connect to remote server using nsurlconnection, fetches the response and display accordingly. While testing the app, I get crashes randomly. If I try to reproduce the crash again I do not get crash. I do not understand what is root cause of the crash. I enable NSZombie,symbolicated crash logs,checked the memory leak but no luck.
I started the project in Xcode 3 and now I imported same project to Xcode 4.2, so are there any issues with compatibility of Xcode?
And I use the same name for nsurlconnection in all tabs like
In Tab 1 I defined nsurlconnection as conn and Tab 2 defined nsurlconnection as conn.
Does this definition causes any issue?
Please help me solve this random crashes
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL: url];
conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];
if(label != nil){
progressView = [[ProgressView showHUDAddedTo:self.tabBarController.view animated:YES] retain];
progressView.labelText = label;
}
[request release];
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSLog(#"didReceiveresponse");
if ([response isKindOfClass: [NSHTTPURLResponse class]]) {
if([(NSHTTPURLResponse *)response statusCode] == 200){
}
else{
//show Connection Error Alert
}
}
responseData = [[NSMutableData alloc]init];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
NSLog(#"didReceiveData");
[responseData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
[progressView hide:YES];
NSLog(#"didFail");
//show failed alert
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(#"didfinish loading");
if([responseData length] > 0)
{
//handles response data
}
}

Answer 1

My guess without seeing code, would be that in a tab your making an NSURLConnection and doing something with the result when it completes. If you change tab before the result is returned then it is causing it to crash.
You need to cancel the NSURLConnection when viewDidDisappear, or make sure that whatever code is run on completion of it doesn't contain anything that would cause a crash if the tab isn't visible (like setting a labels text).
The way I handle this, is have a separate class that performs the URL requests that sends a notification when it's complete. That way in your viewDidAppear method you set your viewController to listen for the notifications, and in the viewDidDisapper method you stop listening for the notifications. So if your view isn't visible when the URL request finishes, the notification is fired but nothing happens.

Answer 2

Could you provide the output of the console? It seems not to be an error from Xcode.
These type of error usually appear when you try to access a deallocated object.

Answer 3

i am sure you have tried Instruments with memory leak. give a try with instruments with zombie tool, you can find it easily in instruments library.
run your code with this tool and if this crash is because of any zombie object then you will easily able to detect the location.
it has helped me few times.