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In my app, I am loading several images onto a UIScrollView and I highlight a portion of the scroll view using Core Graphics routine. I have used the CGImageRelease and CGContextRelease to manage the memory during the routines.

When I run the app using instruments (allocation), I see that the memory consumption keeps rising with every swipe of the scrollView. This at one point leads to the app becoming really slow.

For loading different images, I use the UIImage ImageNamed method, I have come across some posts indicating that this is not a good idea since the method results in autoreleased images which creates memory issues. I would like to know if I am looking a the right place for the error. What could be the possible place to look for this unusual memory consumption?

Also, using the allocation of Instruments, I can just see that increase in the memory, is it possible to pin point the code where these allocations happen?

Thanks in advance for your help!

Best DKV

DKV
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1 Answers1

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For loading different images, I use the UIImage ImageNamed method, I have come across some posts indicating that this is not a good idea since the method results in autoreleased images which creates memory issues.

No, that's not the issue. Anything that doesn't involve you calling alloc, init[WithSomethingOrOther:], and release yourself is going to get the image autoreleased.

The problem is that imageNamed: continues to own the image after it hands it to you. Every image you obtain from imageNamed: stays in that cache, permanently associated with that name. It's not merely a “load this image” method; it's a “load this image and keep it alive forever*” method.

*Where “forever” means “until the end of my process”.

I would like to know if I am looking a the right place for the error. What could be the possible place to look for this unusual memory consumption?

In Instruments. It will tell you exactly how many of each kind of object you are creating, and how much total memory objects of each kind are occupying, and you can sort that list to determine what's eating up memory. Then you can drill down into each class and into each object to determine what's keeping objects alive after you need them.

Peter Hosey
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  • may I ask how do you know "it's a 'keep it alive forever' method"? Can I get a official reference or statement? – Ruobin Wang Oct 28 '14 at 04:55
  • @JimWatson: [The documentation](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIImage_Class/#//apple_ref/occ/clm/UIImage/imageNamed:) is vague on the details, but does say that it keeps images in a cache. Anything more specific is observed behavior, subject to change—and indeed, this might have changed already in the intervening nearly four years: they may have since implemented eviction under memory pressure. But, if it isn't documented, I wouldn't rely on it. – Peter Hosey Nov 16 '14 at 19:05