NSData setLength EXC_BAD_ACCESS - ios

Question

I am developing an IOS application. setLength method crash in didReceiveResponse. What do you think is the reason for this. What should I do prevent.
- (void) callService:(NSString*)urlString
{
NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:[NSURL urlString]];
[theRequest setHTTPMethod:#"POST"];
[theRequest setHTTPBody:[urlString dataUsingEncoding:NSUTF8StringEncoding]];
theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if(theConnection) {
self.webData = [[NSMutableData data] retain];
}
else {
NSLog(#"connection is NULL");
}
}
#pragma mark Web service
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[self.webData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[self.webData appendData:data];
}

Answer 1

Usually, a crash on NSData usages are in fact an early release problem. A NSData initialized with [NS(Mutable)Data data] is an autoreleasable object, even though you called a retain on it.
To be sure this object doesn't get released before your didReceiveResponse gets called, initialize it with [[NSMutableData alloc] init]. That should do it

Answer 2

It looks like you got your memory management wrong.
In this case it's probably an overreleased NSMutableData. Proper management for this object should be done by the property webData. You did not post the declaration, yet it should be along the lines:
#property (retain) NSMutableData *webData;
If you synthesized the accessors they should do the retain/release for you.
To answer why the error happens nevertheless we need more code.

Answer 3

Try this, it may be help you:
this may be crash due to NULL response data so check your response data and set the following condition for the future purpose:
And synthesize your NSData:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
if(responseData != NULL)
{
[responseData setLength:0];
}
}