Memory allocation, release and NSURLConnection in iPhone app

Question

I'm hoping someone can help me with this. I'm struggling to find an answer to what should be an easy question. By the way, this is my first major obj-c project after years of using c and c# so feel free to point out things I'm failing on.

I have an iPhone app designed to load an album of photos into a UIScrollView. It also has a random image function which uses the same process but only displays a single image. It works like so:

1. Read an external XML feed (stored on ruby-on-rails website) which contains a path to a random url of photo once parsed.
2. Content of URL is downloaded using NSURLConnection to NSData.
3. ScrollView is created and pushed
4. Subclassed UIView allocs an UIImageView, allocs a UIImage with the NSData which, inits the UIImageView with the UIimage and finally adds the imageview to the UIView.
5. The parent view then adds the UIView to the UIScrollView which is then pushed to the front.

This process occurs again when when the next random image is required. It also uses the same process when displaying an entire album of images except several UIViews are added to the UIScrollView.

The problem is, despite using release and delloc where appropriate, the activity tool indicates that the memory used by NSURLConnection and UIImage isn't being released from memory when the next image is requested. This is further proven by building the app to the iPhone. Requesting several images in a row causes the app the crash presumably from memory consumption.

Below is some of the code as I'm unable to post the entire project due to contractual agreements.

URLDownload class (uses DataDownload)

@implementation URLDownload
    -(NSData *)GetURL:(NSURL *)strURL
{

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    DataDownload *request = [DataDownload alloc];
request.strURL = strURL;
[request init];

NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
while (request.isLoading && [runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]);

[pool release];

return [request urlData];
[request release];

}

DataDownload class

@implementation DataDownload
@synthesize urlData, connection, strURL, isLoading;

- (id)init
{
if(self = [super init])
{

 self.isLoading = YES;

 NSURLRequest *dataRequest = [NSURLRequest requestWithURL:self.strURL
            cachePolicy:NSURLRequestReloadIgnoringCacheData
           timeoutInterval:60];

 /* establish the connection */  
 self.connection = [[NSURLConnection alloc]
     initWithRequest:dataRequest
     delegate:self
 ];

 if (connection == nil) {
  self.urlData = nil; 
 } else {
  self.urlData = [NSMutableData data];   
 }

}

return self;

}

- (void)dealloc {
[connection cancel];
[connection release];
[urlData release];
[strURL release];
[super dealloc];
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
return nil;
}

 -(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse*)response
 {
[urlData setLength:0];
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
 }

 -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData*)incrementalData
{
[self.urlData appendData:incrementalData];
}

-(void)connectionDidFinishLoading:(NSURLConnection*)connection
{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
self.isLoading = NO;
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
   self.isLoading = NO;
}

@end

ImageView subclass

@implementation ImageView

@synthesize strURL, imvImageView, image, currentlyRotated, imgOptionsView, startDate;

- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {    

 self.imvImageView = [UIImageView alloc]; 

 if (self.strURL != nil){
  [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
  NSData *datImageData = [NSData dataWithContentsOfURL: [NSURL URLWithString:self.strURL]];
  [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];

  self.image = [UIImage imageWithData: datImageData];


  CGSize imgSize = image.size;
  CGFloat fltWidth = imgSize.width;
  CGFloat fltHeight = imgSize.height;

  [imvImageView initWithImage:image];

  // If landscape rotate image
  if (fltWidth > fltHeight){
   imvImageView.frame = CGRectMake(-80.0, 80.0, 480.0, 320.0);

   CGAffineTransform rotate = CGAffineTransformMakeRotation(-1.57079633);
   [imvImageView setTransform:rotate];

   self.currentlyRotated = YES;
  }else{
   imvImageView.frame = CGRectMake(0.0, 0.0, 320.0, 480.0);

   self.currentlyRotated = NO;
  }

  [image release];
 }else{
  self.image = [UIImage alloc];
  [imvImageView initWithImage:image];
  [image release];
 }

 [self addSubview:imvImageView];

}

[imvImageView release];

return self;
}

- (void)drawRect:(CGRect)rect {
// Drawing code
}


- (void)dealloc {
[strURL release];
[imvImageView release];
[image release];
[imgOptionsView release];
[startDate release];
[super dealloc];
}

Sample code of how images are being displayed

- (void)displayImage:(NSString *)strURL {
NSString *strFullURL = @"http://www.marklatham.co.uk";
strFullURL = [strFullURL stringByAppendingString:strURL];

self.scroller = [[UIScrollView alloc] initWithFrame:CGRectMake(0.0, 0.0, 320.0, 480.0)];
[scroller setContentSize:CGSizeMake(320.0, 540.0)];
[self.view addSubview:scroller];

CGRect rect = CGRectMake(0.0, 0.0, 320.0, 480.0); 
self.imageView = [ImageView alloc];
imageView.strURL = strFullURL;
[imageView initWithFrame:rect];
[scroller addSubview:imageView];

[scroller release];
[imageView release];

}

The following images show all allocations to illustrate what's happening. 1 shows alloc on startup, 2 shows after first image is loaded and 3 after after second image.

http://www.gretanova.com/misc/iphone/1.png & 2.png & 3.png

Thanks everyone, Lee

Answer 1

A couple of things stick out. For example within the URLDownload class the call to [request release] will never be reached as its placed after the return statement

return [request urlData];
[request release];