iPhone - Memory Leak - NSData dataWithContentsOfUr

Question

Please help! Have been staring at this for 12 hours; and have looked online and can't find solution.

In my application, I use 2 UIView controls in separate pages/controllers:

• UIImageView (retrieve data via NSData dataWithContentsOfUrl)
• UIWebView

Just to isolate my code, and make it easier to explain, I created a new view based project called "MyTestApplication"

1 - I added a simple NSData dataWithContentsOfUrl in the delegate function.

NSData *imageData = [NSData dataWithContentsOfURL:
  [NSURL URLWithString:@"http://www.google.com/intl/en_ALL/images/logo.gif"]];

(Nothing to release here since it's all using convenience functions)

alt text http://img.skitch.com/20081110-j5tn5n7ixph95ys4rpchibaw5p.preview.jpg

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2 - Run it to verify no leaks (as expected)

alt text http://img.skitch.com/20081110-fy2qrkgy47hm4fe2f1aakd4muw.preview.jpg

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3 - Open the ViewController.xib and simply add a UIWebView from the library (no need to wire it up)

alt text http://img.skitch.com/20081110-d63c3yh1a1kqiciy73q8uyd68j.preview.jpg

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4 - Run it to verify there are leaks! (why???)

alt text http://img.skitch.com/20081110-qtxcfwntbcc3csabda3r6nfjg6.preview.jpg

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What am I doing wrong? Please help!

Why would NSData cause memory leak if I'm using UIWebView? I just don't get it. Thanks.

Answer 1

[NSData dataWithContentsOfURL:url options:0 error:&error] did not help me on iOS8.

But following works correctly:

NSURLRequest* request = [NSURLRequest requestWithURL:imageURL];
NSData* imageData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
[[NSURLCache sharedURLCache] removeCachedResponseForRequest:request];

Production code would need also response and error parameters.

Answer 2

I was also having trouble with leaks from NSData's dataWithContentsOfURL: in the iPhone simulator. I found that when I used the other convenience method (dataWithContentsOfURL:options:error:) I would not get the memory leak.

My code looked something like this:

NSURL *url = [NSURL URLWithString:urlString];
NSError *error = nil;
NSData *data = [NSData dataWithContentsOfURL:url
                                     options:0
                                       error:&error];

Link to documentation

Answer 3

I think this is what's happening:

When ViewController.xib is loaded, an instance of UIWebView is allocated and initialized. Since you're not wiring it up anywhere, it's not getting released. I think you need to wire it up and release it in your backing View Controller's dealloc function. I remember having to manually release every object I created in a xib file.

Answer 4

Are you running Leaks on the Simulator? If so, caveat coder. The Simulator will leak memory where the iPhone hardware won't. No simulator is ever a perfect match for the exact behavior of your code on the device.

I would test on the device as well. I just did the same thing on a similar issue with UITableViewController which was leaking in the Sim but not on the phone.