I have a navigation based App with 5 ViewControllers. After inspecting the memory allocation with instruments i found out that memory is increasing permanently. The app starts up with 2 MB and after navigating through all 5 Navigationcontrollers it grows up to 10 MB and counting...
For every allocated object there is a corresponding release in my code (in dealloc or somewhere else), so obviously there are no memory leaks. Instruments also tells me that no memory leaks could be found.
How can I solve this memory problem? At some point of time, after navigating through the views forward and backward an out of memory warning occurs and the background image disappears (I do not deallocate the image so the iphone does it on its own).
How can i determine the source of the "memory leak" problem? Is it possible that images are cached somewhere and hold in memory as long as the app is alive?
I always alloc images like this:
UIImage *kaufpreisImage = [[UIImage alloc] initWithContentsOfFile: [[NSBundle mainBundle] pathForResource:#"kaufpreis_background_green18px" ofType:#"png"]];
The images are under the Resource folder.
I would very much appreciate your help! I can't find a way out of this!
Thank you very much in advance
Regards Phil
Edit:
The only problem remaining is when I try to send an email. I want to send an email which contains multiple html tables and images inside the email body. The images are base64 encoded. After sending multiple mails I recieve an out of memory warning, although I dealloc all the stuff (images, Numbers and so on) inside the sendMail() method.
Does anyone know if sending base64 encoded images leads to problems? Can anyone give me a hint how I can send images inside the emailbody (e.g. as background image inside a html table like style="background-url(data:image/png;base64,%#)")? To clearify, this works. The images are sent to the Client (tested on MacOS) but sometimes the memory problem occurs...
Thank you very much
You need to release those images once you take ownership of them.
Maybe you shall try the 'Heapshot' function in the Allocation tool. Simply take a 'Mark Heap' when your first controller is started then navigate on and again back. Take another heapshot. Repeat this process 8-10 times. In the heapshots list you shall see that some memory has been allocated between an heapshot and the following one (otherwise if the amount is small and tends to zero it is normal), try to inspect it in order to check if you allocate something that remains alive.
You are responsible for releasing the instances of UIImage if you have used [[UIImage alloc] init...] to create them.
If you are loading images from the main bundle, try using +(UIImage *)imageNamed:(NSString *)name. This UIImage returned is returned autoreleased, so you don't have to release, and there is the upside that UIKit handles caching when using the imageNamed method.
Related
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)??
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!
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?
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.
So apparently, my app crashes on ipod 2nd generation due to low memory issue. What I do was calling image on each view within scrollView + pageControl when user scrolls. And app crashed when it reached a particular point after got memory warning. I tried to free up view when I got warning but it still caused crash.
I googled about ImageNamed: and apparently there was issue within this api call, but most article said it was fixed in recent iOS version.
I fixed this problem with calling image imageWithContentOfFile instead imageNamed, but I'm wondering if ImageNamed still causes memory leak or not free up when it view is released.
imageNamed: doesn't cause a leak, but it is frequently misunderstood which is what leads to memory issues when it's used. It caches the uncompressed image after it is loaded, which means there are immediately 2 copies of that image in memory. If you use it for small, frequently used images (such as icons), this is great because the runtime doesn't have to fetch the file off disk - it's already available in the cache. Where this gets users into trouble is when they use imageNamed: to load a large image, say a 4MP image taken with a camera. That image takes up quite a bit of memory: 4 million pixels, types 4 bytes per pixel = 16MB of memory, TWICE. If you use that method to load images for your slideshow, photo sharing, camera app, or whatever, it adds up real fast.
So if those features don't fit what you need, use one of the other UIImage loading methods. You users will thank you.
Note: This information comes from the Apple Engineer which presented the UIKit rendering session (#121 I think it was). Hopefully my notes are correct :)
I have two queries
I was running a sample app which having single view controller in it implemented. When I check the memory using Instrument it was showing 3.66 MB
. Wondered why it is taking so much of RAM as there is nothing much heavy in app.
When I have added UIImageview with the Image having size of 25 KB,then Memory uses go to 4.24 MB
[ I come to know the reason behind is "image is unpacked 320*480*4 = 580 KB" but need to debug more on this & it remains in cache ]
Along this I have also observed two scenarios
When we uses api [UIImage imageNamed:aName] for loading image, then calling [UIImageview release] doesn't have any effect.
But When we use
[UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:aName ofType:nil]];
Some memory is cleaned up when I call [UIImageview release]
In my app , I am going to use lot of images and that will cause a low memory and will crash the app.
Please provide me some ref or path to analyse why this behavior.
Thanks,
Sagar
Trying to fit your app in memory is a losing game. It'll lead you down weird paths of trying to figure out which sort of device you're running on, swapping in and out resources based on that, etc, etc.
The better option is to design your memory structure for ditchability, and then support a fairly harsh ditching regimen when you're notified of low memory conditions. Go ahead and use memory--it's there for that--and let the low memory warning be your signal to prune out unused resources.
A lot of people seem to feel bad that their application generates memory warnings. That's silly. The design pattern here is, eat all you want, but respond appropriately when you're told you're overweight. Given you're running on a broad range of devices with a broad range of memory profiles (an iPhone 3G has 1/4 the RAM of an iPhone 4 for instance), the best way is just to be sensitive to when you've filled memory.
The main hurdle you'll encounter is recovering from having ditched data. I find what works best is to explicitly set UIImage objects to nil, and then test for nil before using them, reloading them from the bundle or the network or whatever if necessary.
All that said: [UIImage imageNamed:] supports ditchability, but you don't have control over it. When a UIViewController subclass gets a memory warning, it will ditch cached UIImages that you've created with that method, but nothing you can do will make them go away until then. Even assigning a tiny something to the UIImage in question won't help because it's cached associated with the "name" that it's "Named", not the object that it is assigned to. So that method is good for images you're going to reuse a lot, but even so, it will get pruned when the time comes, and you need to respond appropriately.
Images, loaded with imageNamed, are cached in memory by UIKit, and images, loaded with imageWithContentsOfFile are not.
According to the UIImage documentation:
In low-memory situations, image data may be purged from a UIImage object to free up memory on the system.
Does anyone know how this works? It appears that this process is completely transparent and will occur in the background with no input from me, but I can't find any definitive documentation one way or the other.
Second, will this data-purge occur when the image is not loaded by me? (I'm getting the image from UIImagePicker).
Here's the situation: I'm taking a picture with the UIImagePickerController and and immediately taking that image and sending it to a new UIViewController for display. Sending the raw image to the new controller crashes my app with memory warnings about 30% of the time. Resizing the image takes a few moments, time that I'd rather not spend if there's a 3rd option available to me.
I think this is the answer. In the documentation for initWithContentsOfFile: it says:
This method loads the image data into memory and marks it as purgeable. If the data is purged and needs to be reloaded, the image object loads that data again from the specified path.
None of the other methods in UIImage mention purging, so it appears that initializing a new image from a file is the only way to get this low memory behavior.
In answer to your second question: Save it to a file, and then use:
[NSData dataWithContentsOfMappedFile:]
to do the resizing. Using a files as intermediates, is rather slow though.
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.
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.
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.
As the API reference of UIImage says :
+(UIImage *)imageNamed:(NSString *)name
This method looks in the system caches for an image object with the specified name and returns that object if it exists. If a matching image object is not already in the cache, this method loads the image data from the specified file, caches it, and then returns the resulting object.
+(UIImage *)imageWithContentsOfFile:(NSString *)path
This method does not cache the image object.
so,we can see that if you have a lot of same UI elements(such as UITableViewCell) that may use same image(often as an icons),and due to performance , of course we want to reuse the same image , so that we will save some memory for other use . Generrally the reused image is often used in the ui element that our user may operate on it lots of times . So it values for us to reuse it .So you can choose to use imageNamed method .
And on the other hand , in an application , there will be some UI element that will be there during the app's life cycle,such as a Button , a logo view , so these images used by these ui elements may also be there during the app's life cycle ,you wouldn't consider whether these image should be cache or not .So you can choose to use imageNamed method .
On the contrary,in an application , there are often some UI Elements that created dynamically. For example , our application support dynamic background , so that user can choose the background they like .And the background may be an image .So we may have a interface that list lots of different background (often show by use UIImageView) for user to choose ,we can name the list view MyBackgroundListView.So once the user chooses an background image , the MyBackgroundListView should be destroyed , because it has finishs its function .The next time the user want to change his/her background , we can create MyBackgroundListView again .So the images used by MyBackgroundListView shouldn't be cached , or our application's memory will run out .So this time you should use
imageWithContentsOfFile method.
As the Apple's doc Supporting High-Resolution Screens In Views says
On devices with high-resolution screens, the imageNamed:, imageWithContentsOfFile:, and initWithContentsOfFile: methods automatically looks for a version of the requested image with the #2x modifier in its name. If it finds one, it loads that image instead. If you do not provide a high-resolution version of a given image, the image object still loads a standard-resolution image (if one exists) and scales it during drawing.
so you would worry about the image's search path for retina screen problem . IOS will help you deal with it.
Sorry for my poor English . May it be helpful.
If you don't want your image do be cached you can also use initWithContentsOfFile directly :
NSString *fileLocation = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];
UIImage* yourImage = [[[UIImage alloc] initWithContentsOfFile:imagePath] autorelease];
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.
imageWithData is useful when you store your image binary in a database or progressively downloading large image from the web.
I would not use imagenamed if your app has loads of big images which are not the same. I experienced app crashing due to using too much of it.
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.