I'm coding an application on Ipad, in a certain point of my application I present a ViewController with the presentModalViewController.
My ViewController is a UISScrollView who take the larger of the modalView and inside it I display some images, I allow pagingEnabled so I can see all my images inside the scrollView.
Sometimes I have to display more than 10 images inside the scrollView, so I have this error
RECEIVE MEMORY WARNING LEVEL=1 after this one RECEIVE MEMORY WARNING LEVEL=2 and finnaly the debugger exited due to signal 10 (Sigbus).
What can I do? is there a way to unload the image thats offscreen? or others things to do?
Thanks,
I guess you're adding all the images to the UIScrollView? Then the iPad has to keep all 10 images in memory. If they are full screen images, each of them will take up about 3 MB of memory, so you're using 30MB just to keep the 10 images in the scroll view.
You should only add the one or two images that are actually visible. Once they scroll out of sight, remove the UIImageView from your UIScrollView (and make sure you don't retain it anywhere else so it can be deallocated). When a new image scrolls into sight, add it to the UIScrollView only then.
In your UIScrollViewDelegate method -scrollViewDidScroll: get the current contentOffset and use that to calculate which images are visible.
Actually, this problem is even worse on the iPhone 3G, which can't even manage to display two full size photos (taken with it's own camera) at the same time.
If you can make the photos smaller ahead of time by resizing them (server side if you're snagging them from your own services, or client side if they're somehow generated on the device or retrieved from third party services), you should. They will load faster, and you can put more of them on the screen at once without running into memory issues.
The Three20 library has a really great photo-browsing control for the iPhone. I'm pretty sure they only have three photos around at any given time... the photo you're looking at, and the photos going forward or backwards.
http://github.com/facebook/three20
I also think there is an iPad branch of the Three20 controls (at ./tree/ipad), although I don't know if they include the photo browser or not, and haven't tried them yet myself... maybe that's an option for you if you don't want to spend a lot of time on that particular feature of your application. If the iPad photo browser isn't done maybe you could just adapt the iPhone version to suit your needs (shouldn't be hard).
If you want to bake the feature yourself, I'd take some inspiration from the UITableViewController. Your controller should come with associated datasource and delegate protocols to retrieve photos and respond to user events. The controller base class itself should reuse three UIImageViews and should shuffle those around to create the illusion that the user is scrolling through a large list.
Related
I have tiny issue in my app. I load data from JSON and then take image links and load images on cells. Im not sure i really should paste all of my code, since it may not concern the issue. Just want to point i use
[imageView setImageWithURL:url];
and in myCell custom class i use:
- (void)prepareForReuse {
[self.myCellImageView cancelImageRequestOperation];
self.myCellImageView.image = nil;
}
Second code snipper fix the issue when u smoothly scroll table, tableView load correct images. But there is the trick - if u press on status bar on an iPhone (place where your clock, battery charge and carrier name appears) you may get from bottom of your table to top in fraction of second.
During that, application proceed to load wrong images (apparently, recently loaded in bottom cells), and after switching images it set correct one.
I want to admit, that problem almost didn't noticeable if u scrolling with low or medium speed, it only appears when you make enormous move from one side of tableView to another. But still, its nasty bug. How could i fix it?
Thanks!
One of the ways to improve user experience in iOS while showing images is to download them asynchronously without blocking the main thread and showing them....
But I want to add something to this -
Initially when there is no image,show a spinner while the async download has started.
After the download cache the image on local iOS disk for later use.
After the download populate the image part of UIImageView.
And dont just plonk the image into view for user. Showly Fade in the user (i.e. from alpha 0.0 to 1.0)
I have been using SDWebImage for sometime now. It works well but does not satisfy my 1st requirement (about spinner) and 4th.
Is there any help out there to satisfy all this?
Three20 http://www.three20.info has a TTImageView class that statisfies 2-3, you can subclass it and overwrite setImage: and create the fade animation there. (or just modify TTImageView.m directly).
Spinner is easy as well when you modify TTImageView you can add a TTActivityView on top and remove it on setImage:
I'm trying to build a weather application on the iPad but it seems that I need some help in animation. Say I'm animating a Radar, so the radar source files have 10 gif/jpeg pictures in 900x700 pixel size. I've tried the UIImage animation technique using the tutorial here:
http://www.icodeblog.com/2009/07/24/iphone-programming-tutorial-animating-a-game-sprite/
but it seems that loading 10 images that big is too much for the iPad to handle and its crashing due to memory warnings. I'm researching other techniques to animate but I can't seem to find something that will do this efficiently.
I've looked at others like Core Animation using sprites, and Cocos2D with sprites. Can someone point in the right direction the best way to animate these big images? (keep in mind that these images are dynamic and changes often so the sprites will have to be recreated on a server and fetched from the iPad to do the animation). Thanks
OpenGL only creates textures with dimensions at powers of 2. In the case of your images, that's 1024x1024, which is a meg of memory per image. Still, that shouldn't be a problem with the iPad.
First, investigate using Xcode's profiling tools to ensure the images aren't being repeatedly loaded into memory at each loop of the animation (likely by way of new objects that aren't sharing cached textures). That could solve your problem from the start.
Second, I recommend using Cocos2D if only for the easy handling of textures and caching. Toss the images into a CCAnimation, pop that into a CCRepeatForever, run it with a CCSequence. When you're done hit CCTextureCache to release unused textures.
Third, lower your animation framerate to 30 or less (if only for this animation). It may be the iPad, but you making a weather app. Not a video game.
Finally, downgrade the size of your image. Justify all you want, but a large radar animation will not sell your app. And just because a website might already be playing that animation beautifully, remember that a desktop has vastly more memory and power than any smart phone.
Try breaking the animation image into into smaller parts and animate those instead by treating each components as sprites. It would be best if you use primarily code (CoreGraphics) and draw your radar "by hand" instead of just using images as if they were animated GIFs.
I want show per page pdf in portait mode and display two pages when rotate to landscape mode on ipad . I had search on internet and can't find any solution. I thought two possible way.
1.Using webview but I don't know how to display two page in one webview in a webview.
2.Using CGPDF API read from two page and merge to one pdf file. But I think this may be very slow and not sure if this could do it .
or any other way could solve this problem? Thanks!!
I don't think you will have much success with using a UIWebView there. There's however nothing stopping you from putting two CATiledLayers into a UIView and display them next to each other. In fact, that's exactly what I did in my iOS PDF parsing framework.
Just set the contentView as the containerView, that includes both tiled layers, and they work perfectly together. Keep an eye on your memory though, I wouldn't allow them both rendering pdf at the same time, that most likely crashes your app due to low memory. (Drawing a PDF is really resource intensive)
In a project that I am currently working on I have an transparent NSWindow overlayed on a QTMovieView. At certain points I slide a custom view into this child window with animation so that it is displayed over the movie for a short period of time. The only odd behavior is that the animation is smooth on a Mac Book Pro but on a Mac Book(Same OS-X Version) there is significant flicker. The flicker only occurs on the portion of the window that has the actual QTMovie behind it.
Has anyone seen this behavior before or found a way to work around it?
The older MacBooks don't have real video hardware and used shared memory, so it's probably an issue with a slow video card trying to update # 30fps. Have you tried smaller movies to see if the issue goes away?
You may be better off with a pipeline like in the QTCoreVideo101 sample code from Apple. That would be a bit more work, you'd have to take care of the animation yourself, but you would get ultimate control over what is being drawn.