R – iPhone Development – Lessons in memory management


I need lessons in memory management. I have an application that uses multiple views (around 10), some of these are attached to tab controller. Problem is that I'm using images (many images that I load from a web service). I'm facing the following issues.

  1. The memory keeps increasing when I scroll in the table view (why?) – I checked the CustomTableViewCell application from Apple's site, and it's showing the same signs when I run it with Instruments.

  2. I'm using autorelease with many objects, but I see that these objects don't actually get released and the memory is wired. How can I get rid of these objects?

  3. How can I tell the NSAutoreleasePool to periodically release the objects that are not being used? I think this can help me get rid of wired memory. But can I do that?

Is there any example by Apple or someone else (book or online articles) explaining how to use Instruments (in a little detail with example?) and to fine tune the application for memory and performance?


Best Solution

Now that we have the "just say no" answers to autorelease out of the way, I thought I'd add a tip on how to use autorelease more effectively. For better or worse not everyone's going to completely avoid autorelease-- if for no other reason than because Apple provides so many convenience methods that hand you autoreleased objects.

You can't just tell the autorelease pool to free up any objects that you're not using. There's no garbage collection, and how else is it going to know?

What you CAN do is to create a local autorelease pool and then release that when you no longer need the local autoreleased objects. If you have a block where you're creating autoreleased objects, you'll ensure they get freed by creating a local autorelease pool at the start of the block (just alloc/init it, no magic required) and then releasing the pool at the end of the block. And voila, and objects in the pool are also released.

Autorelease pools nest, so keep that in mind if you do this. If you release an autorelease pool, make sure it's the most-recently-allocated pool and not some other one.