Message sent to deallocated instance in iPhone - iphone

Question

I am new to iPhone,
I am creating NSURLConnection as suggested by apple here
but my app crashes when i Dismiss my view, i have tried concept of NSZombieEnabled which shows me -[CALayer release]: message sent to deallocated instance 0x68b8f40
I am displaying a webpage in Webview, When users clicks on download link in the webview then shouldStartLoadWithRequest method will be called inside this method i am creating NSURLConnection.
here is my code snippet,
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data1
{
[receivedData appendData:data1];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(#"Succeeded! Received %d bytes of data",[receivedData length]);
DirPath=[self applicationDocumentsDirectory];
NSLog(#"DirPath=%#",DirPath);
[receivedData writeToFile:DirPath atomically:YES];
UIAlertView* Alert = [[UIAlertView alloc] initWithTitle:#"Download Complete !"
message:nil delegate:nil
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[Alert show];
[Alert release];
// release the connection, and the data object
[connection release];
[receivedData release];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error1
{
[connection release];
[receivedData release];
// inform the user
NSLog(#"Connection failed! Error - %# %#",
[error1 localizedDescription],
[[error1 userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (BOOL)webView:(UIWebView*)webView shouldStartLoadWithRequest:(NSURLRequest*)request navigationType:(UIWebViewNavigationType)navigationType {
//CAPTURE USER LINK-CLICK.
Durl=[[url absoluteString]copy];
//Checking for Duplicate .FILE at downloaded path....
BOOL success =[[NSFileManager defaultManager] fileExistsAtPath:path];
lastPath=[[url lastPathComponent] copy];
if (success) //if duplicate file found...
{
UIAlertView* Alert = [[UIAlertView alloc] initWithTitle:#"This FILE is already present in Library."
message:#"Do you want to Downlaod again ?" delegate:self
cancelButtonTitle:nil
otherButtonTitles:#"Yes",#"No",nil];
[Alert show];
[Alert release];
}
else //if duplicate file not found directly start download...
{
// Create the request.
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:Durl]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// create the connection with the request and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData to hold the received data.
receivedData = [[NSMutableData data] retain];
} else {
NSLog(#"Inform the user that the connection failed.");
}
return YES;
}
Any help will be appreciated.

Answer 1

Make sure that in your implementation of dealloc you are resetting the delegate to nil. Another place for doing so would be viewWillDisappear:.
The reason for your app to crash / access a zombie is that the UIWebView instance will possibly be trying to call back the viewController even though it has already been deallocated. To prevent that, you have to set the delegate of that UIWebView back to nil before the viewController goes out of scope. That is a general issue when working with delegation prior to iOS5's ARC implementation. iOS5 finally offers weak references, those actually nil themselves once their instance is getting deallocated.
Example A:
- (void)dealloc
{
[...]
_webView.delegate = nil;
}
Example B:
- (void)viewWillDisappaer:(BOOL)animated
{
[super viewWillDisappaer:animated];
_webView.delegate = nil;
}
Edit:
After reading your question once again, I realised that the zombie is a UIView or a UIControl since the message is sent to a CALayer. Make sure your problem actually is related to the web view by temporarily removing all webView related code.

Answer 2

I think issue with this NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
You are creating an instance of NSURLConnection with delegate self, when you dismiss the view everything get deallocated on that view. But when the NSURLConnection tries to call it's delegate method crash will occur.
So you need to set the delegate of NSURLConnection to nil in your viewWillDisappear for doing this, you need to create object of NSURLConnection in interface.
#interface yourClass
{
NSURLConnection *theConnection;
}
#end
in .m
theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
- (void)viewWillDisappaer:(BOOL)animated
{
[super viewWillDisappaer:animated];
theConnection.delegate = nil;
}