I'm working on an iPad-App with ARC which have to display thousands of UIImageViews in a UIScrollView...
When I load them all at once (or more accurately in a queue with GCD), I run out of memory after a while of loading..
Now, I thought i have to use lazy-loading and load only those UIImages which are necessary and a kind of release those which are no longer visible, but I don't know if this is possible with ARC..
Anybody have an idea to do this, or a better idea to handle this case..?
Thanks, tonistair
Make something that implements UIScrollViewDelegate, and in its viewDidScroll method, calculate the currently visible rect from contentOffset and bounds. Then remove things that are no longer visible, and add things that have just become visible (or some other appropriate algorithm). ARC has nothing to do with this.
Related
Here is the problem :
I am writing an app which displays some pictures, with a treemap layout (for an example, see https://raw.github.com/beckchr/ithaka-treemap/master/Core-API.png)
This layout is displayed in a UIScrollView. Since many pictures can be added to that scrollview, I want to release the ones which are not on currently on screen. I am not using ARC.
At my point, I know which pictures I should release, and how to do it while scrolling (calling some "unload" method). There is no useless call of that method. The problem is that, when pictures are released, the scrolling stops for a little moment (a few ms, but this is enough to be bad looking, making the scroll kind of "jumping" and slow, not smooth at all).
What I've tried (put in the body of my "unload" method) :
imageview.image = nil
performSelectorInBackground:#selector(effectiveUnload) withObject:nil
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0,^(void){
dispatch_sync(dispatch_get_main_queue(), ^(void){
imageview.image=nil}
}
I think this problem is weird, since there is absolutly no slowing effect with memory allocation, but only with memory release.
Thanks for help, don't hesitate to ask for more information.
did you try removeFromSuperview to remove the imageview from scrollview
Don't add more and more UIImageViews - recycle them!
To save as much memory as possible you should follow the UITableView way of recycling views:
1. Once a view has left the visible area, add it to a "views pool" (and remove it from its superview. It's not an expansive operation!)
2. When a new view becomes visible, first check if there's a view in the pool. If not, then create a new view.
I know my answer doesn't answer your question directly, but that's the way to go. Otherwise you'll run out of memory eventually.
We have an out-of-memory crash on the iPad 3 which we traced to the following scenario:
A UIView which uses a CATiledLayer and draws content (say, a PDF) has subviews with their own drawRect methods (which, for example, highlight search results). This makes Core Animation consume tons of memory (100+ MBs in the VM Tracker instrument), and can easily lead to a crash. While this issue exists on all devices, only on the iPad's Retina display does the cache size grow too large.
This can be reproduced with Apple's PhotoScroller example: subclass UIView, uncomment drawRect, and add an instance to the TilingView. The app will crash on iPad 3. Commenting drawRect resolves the memory usage.
Now, we can drop the subviews and do the drawing in the top-most UIView. However, working with subviews is convenient (since we're representing different, independent layers on top of the PDF). Two questions:
What is a good work-around? Preferably one that allows us to continue working with multiple views.
Why is this happening, exactly? I guess the cache mechanism is working overtime, but it would be great to understand the technical details behind it.
Thanks!
EDIT:
I want to elaborate on Kai's answer. The problem was indeed unrelated to CATiledLayer, but to the usage of UIViews that implemented drawRect.
In the case of PhotoScroller, I created a UIView which was of a size of the image - 2000x2000 and more, which creates a huge backing store if drawRect is present.
In the case of our app, the overlay views are full-screen (=~11 MBs on iPad 3) and we have about 5 of them per page. We keep up to three pages in memory while scrolling, and that means more than 150 MBs extra memory. Not fun.
So the solution is to optimize drawRect away, or use less such views. Back to the drawing board it is :-)
To 2.: Whenever you implement drawRect in a UIView subclass and have lots of instances of that class, your memory usage will grow dramatically. Reason is that a lot of optimization tricks in UIKit view/subview handling (e.g. when zooming or scrolling) don't work with such objects, because the framework doesn't know what you're doing/what you are drawing.
So - independent of retina or not - avoid implementing drawRect, especially when having many objects or many layers of subviews.
To 1.: I didn't exactly get what you are trying, but I implemented an PDF-Viewer which is also able to show additional content on top of the PDF. I did it all with normal UIView hierarchies, images etc. and I fear that's the only reliable work around you'll get
My experience:
Never add subviews to a UIView that's backed by a CATiledLayer
Never add sublayers to a CATiledLayer
Unfortunately, that seems to be the only practical answer - Apple's implementation goes horribly wrong in many different ways (not just performance - the rendering itself starts to exhibit visual artifact bugs, some of Apple's rendering code goes weird, etc).
In practice, I always do this:
UIView : view
+-- UIView w/ CATiledLayer : tiledLayerView
+-- UIview : subViewsView
...and safely add views and subviews to "subViewsView". Works fine.
I've run across a couple of similar questions here regarding getting an animated MKOverlayView working property with decent performance (e.g., an animated radar overlay). However, while the answers have helped lead me in the right direction, I still don't fully grasp what I'm missing yet.
I've been trying to get this UIImageView method working, which simply adds an UIImageView as a subview of the MKOverlayView, then adds the necessary images in the animation sequence to its animationImages property. This doesn't seem to work for me as the UIImageView and its associated images are never rendered. I've even tried calling setNeedsDisplay on the overlay view which also doesn't help. In my instance, the images used in the animation have to be loaded from a remote server first and are updated fairly frequently.
There's also this method that suggests using cocos2D to setup an animated sprite, which I'd like to avoid if the above method with UIImageView works successfully.
I've been struggling with this for two days straight now, so there's likely something I'm totally missing? Do I need to use Core Graphics to do the drawing similar to how it's performed in the main drawMapRect:zoomScale:inContext: method (which I've also tried but didn't work)?
Maybe you can try this. Subclass the MKCircleView and animate a UIImageView added on it with Core Animation. It works well with the map moving around and scale with the map zoom in and out.
http://yickhong-ios.blogspot.com/2012/04/animated-circle-on-mkmapview.html
OK so in my game I need the users to scroll between items, just like you scroll a web page in Safari. Is there any way to do that? If not, maybe scrolling them to the side, like you do in the spriboard? Thanks.
I am not really sure I have understood what you would like to do, but there is a cocos2d extension that seems appropriate to it: CCScrollLayer.
CCLayer subclass that lets you pass-in an array of layers and it will then create a smooth scroller. Complete with the “snapping” effect.
If you are looking for a generic scrolling within your view, I suggest this tutorial or this topic rom cocos2d list.
EDIT:
I have never done it, but I think it should be possible to scale the CCScrollLayer to the size you need.
Otherwise, you might change the contentSize of the layer, or even put the CCScrollLayer into a clipping node.
Anyway, I think that it is much easier to start from this and find a way to adapt it to your specific requirements than start from scratch.
I have two uiimageview animations. One on each of two view controllers in a navigation controller.
They have about 10-15 frames each. This is the smallest I can possibly make them.
They seem to be using a hell of a lot of memory though. Especially on startAnimating. Is there any way around this?
On my iPad this is causing a memory warning an a leak. I've tried looking into it, and as per an earlier question on here I've been using a lot of memory tools and such and narrowed the issue down to the startAnimating function.
I have read that this is because on startAnimating the imageView puts all the images into memory at this point.
However removing from superview and releasing dosen't seem to have a marked effect on the amount of memory reclaimed.
Is there any way around this? Bar creating a custom OpenGL style animation?
Thanks
Even i use to face same Problem.. I came up with solution by using custom navigation controller. Now i don't see any memory warnings or memory leaks.
Try to implement your own custom navigationController.