CODEWITHSUNDEEP
iphoneobjective-ciosipadmemory-management
Jordan Smith
Jordan Smith

Reputation: 10378

Images not freed on memory warning when using [UIImage imageNamed]

In my app, I've used the line

[UIImage imageNamed:imageName]

whenever loading an image. As I understand it, this function caches images for later use - this is great, because most of the images are used more than once.

BUT - when I simulate a memory warning, the memory used by these images doesn't seem to be freed according - and since most of the memory is in fact used by the cached images, it is pretty important that any currently unneeded images are released from memory!

-

Is this the expected behavior, or do the images remain in memory due to the fact that it's only a simulated memory warning? Or, if I want to release these images, will I have to write my own category for UIImage that caches images but releases uneeded ones when memory is in short supply (or even better, has anyone already done this/shared the code for it)??

Upvotes: 2

Views: 2633

Answers (3)

skram
skram

Reputation: 5314

What I have done is create my own caching mechanism utilizing -initWithConentsOfFile which doesnt cache, and an NSMutableDictionary for storing, every image allocated is stored in the dictionary with the image name as the key. If a memory warning is reached you can release and nil the dictionary thus releasing all the memory allocated from the images.

This gives you complete control over the image caching. -imageNamed: uses its own caching mechanism that you have no control over when and where the allocated memory is released.

You should try this method as well.

EDIT: Heres my UIImage class extension (https://gist.github.com/2880240), overriding -imageNamed: with custom cache, upon receiving a memory warning you can simply use [UIImage freeCache]. Also included, is the ability to set autorelease on all images upon storing them in the cache, i.e: [UIImage setShouldAutorelease:TRUE]. FALSE by default.

Give it a try, Hope it helps!

Upvotes: 4

Scrungepipes
Scrungepipes

Reputation: 37600

Are you using it in a UIImageView?

A lot of framework data is automatically managed with the app goes into the background. Data for images loaded with imageNamed: are discarded automatically, but UIImageView does not discard its data, so perhaps its the same with the low memory warning.

P.S. If your app is suspended it won't receive the memory warning. And if its using a lot of memory then it'll probably be terminated. To reduce the chances of this (if its important) then you could use an NSPurgeableData which you store in an NSCache in order to flag stuff as being purgeable in the event of a low memory situation, the OS will then purge it for you.

Upvotes: 0

Jake
Jake

Reputation: 3973

If there is no more reference to the image it should get cleaned, don't worry about the internal caching mechanism (since its behavior is undocumented anyway). Do you have any code in place to remove any references (nil or release) to the images?

Upvotes: 0

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