Difference between [UIImage imageNamed...] and [UIImage imageWithData...]?

rustyshelf_6044 0
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I want to load some images into my application from the file system. There's 2 easy ways to do this:

[UIImage imageNamed:fullFileName]

or:

NSString *fileLocation = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];
NSData *imageData = [NSData dataWithContentsOfFile:fileLocation];

[UIImage imageWithData:imageData];

I prefer the first one because it's a lot less code, but I have seen some people saying that the image is cached and that this method uses more memory? Since I don't trust people on most other forums, I thought I'd ask the question here, is there any practical difference, and if so which one is 'better'?

I have tried profiling my app using the Object Allocation instrument, and I can't see any practical difference, though I have only tried in the simulator, and not on an iPhone itself.

iphone cocoa-touch
8 Answers

It depends on what you're doing with the image. The imageNamed: method does cache the image, but in many cases that's going to help with memory use. For example, if you load an image 10 times to display along with some text in a table view, UIImage will only keep a single representation of that image in memory instead of allocating 10 separate objects. On the other hand, if you have a very large image and you're not re-using it, you might want to load the image from a data object to make sure it's removed from memory when you're done.

If you don't have any huge images, I wouldn't worry about it. Unless you see a problem (and kudos for checking Object Allocation instead of preemptively optimizing), I would choose less lines of code over negligible memory improvements.

Marc_Charbonneau_351360

In my experience [UIImage imageNamed:] has dramatically better performance, especially when used in UITableViews.

It's not just the memory but also decoding the image. Having it cached is much faster.

user_5550

I've also been told that [UIImage imageNamed:] does a little bit too much caching, and images are not often released. I was told to be careful of using it.

Ben_Gottlieb_66940

imageWithData is useful when you store your image binary in a database or progressively downloading large image from the web.

user_97740

I don't believe that the image gets cached at all, and I don't know why you are all saying that. UIImage is a subclass of NSObject which uses reference counters to keep track of the things that it is related to. So when you load an image it does that same thing. If you load the same image multiple times it will(or should) have only one copy of the image in memory and just increment the reference counter every time you have to use something with that image. By Reference Counters I mean that when the count gets to 0 it deletes itself. so "alloc", "retain" are each +1 to the count and "release" is -1. Not only is it a better way to manage memory but this style of programming also helps clean up memory leaks.

user_5458200
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