I see in many WWDC video's that says you want to achieve 60.0 FPS as close as possible to get a better smooth scrolling experience. I have a UIScrolLView which loads up image and a couple of table view's at once. Currently I am getting 30 FPS. This is half of what the recommended FPS. Just wondering what FPS do you guys typically get for a table view/scroll view that loads up images and other heavy stuff/rendering stuff.
Any other tips for optiziming FPS? I've spend the past week till now firing up Instruments using the time profiler, allocations, and core animation tool to optimize as much as I can.
Just to clarify a bit on what I have. I have a masonry/waterfall/pinterest style layout on the iPad. So it's not just a regular UITableView. It's a UIScrollView that fills out the whole screen, and is filled with a couple of UIView's. Each of this view has a 150x150 UIImageView and a UITableView and also it has some attributed label, drawn using Core Text. So at one glance when you see the screen, you can see 5-8 table view at one shot, each cell again has a UIImageView and then each cell renders attributed label drawn using core text.
So you can just image how deep and complicated this is. This is not just a regular table view with a UIImageView. I know how to get 60 FPS with just one UITableView in an iPhone with a UIImage. The concept is to load images asynchrounously and not to block the main thread as much as possible.
EDIT:
It seems that the problem here is the UITableView that I have inside my view.. when I remove that from the UIView I get really smooth scrolling..
I uploaded a sample project which is a simpler version of what I have, but it clearly shows the problem. The link is here
Many things affect render performance, here are some items you can check:
Profile - You said you already did this, so great job! Unfortunately profiling is often overlooked, even though it can reveal unexpected problems. In one app I was working on a calendar with different cells representing dates. At first scrolling between cells slow, which was unexpected. I thought maybe it was drawing a few cells too many. After profiling I found that [NSCalender currentCalender] was using 85% of my CPU time! After fixing that everything scrolled great!
Images - Large images put a lot of load in CoreGraphics. Scrolling especially requires a lot of draw operations to move them around. One tip is to scale images on the device as little as you can, that makes CoreGraphics' job a lot easier. If an image is twice as large as the view displaying it, resize the UIImage before displaying it in the view. iOS devices handle PNGs best. They are compressed by a tool (pngcrush) at compile time and iOS has special hardware for rendering them.
Edit: JPGs are probably a better option for photos. iOS devices have dedicated JPG decoders as well.
Custom Drawing - If possible, cutback on the amount of custom CGContext drawing you do. Lots of custom drawing has negative effects on animation speed. I would considering using an image over complex custom drawing, if possible.
Cull - Only draw things you need to. UITableView automatically unloads and loads cells as they appear, so this is done for you, but any custom CGContext drawing should only be done when that part is visible. Also automatic view shadows can be very slow in my experience.
Reuse - Use the reuse identifier on UITableView, this will allow UITableView to reuse cell objects rather than reallocating as it scrolls - look at the answer to this question. Also reuse UIImages rather than allocating multiple for the same file. imageNamed caches images automatically but imageFromContents of file does not.
Create your own - You could create your own grid view class that culls it's subviews views hidden off screen, and scrolls with lazy content loading. By writing a custom solution you can fully control the process and create a design optimized for the usage context. For most use cases you will have a hard time building something better than the Apple standard, but I have seen it done in specific cases.
Last resort - Reduce the size of the offending view (improves filtrate), break content into multiple pages, downsize images, cut out older devices that don't perform as well. I would settle for 30 FPS before sacrificing most of that stuff. Devices will continue to get faster, older devices will be eliminated, and your app will gradually get faster.
I get close to 60 fps with my UITableViewController where the table contains about 2000 cells and each cell pulls an image from the web. The trick is to lazy load the images as you need them. This sample code from Apple is pretty helpful.
The general idea is to keep the UI responsive by not blocking the main thread. Perform downloads and other time-consuming tasks on another thread.
I would do something called Lazy Loading, which doesn't load the images until they are actually seen.
Here's a great example on how to do so: http://www.cocoacontrols.com/platforms/ios/controls/mhlazytableimages
Good Luck!
What I've done is to use NSCache. I've created a small class with properties that conforms to the NSCache data protocol (its really easy to do). So what I do is create a relationship between each cell in the main table and various things worth caching: NSAttributed strings, images etc - really anything that takes work to create. I don't preload it but you could.
When you are asked to provide a cell by the tableview, look in your cache for your primary object. If there, pull all all the objects you need. If the cache does not have the object, then get the data the old fashion way, but before you finish, save it in the cache too.
This really helped me reduce "stutter" when scrolling the cell. Also, do NOT animate anything in the cell - that kills performance. Everything should be fully rendered.
Another thing to remember - make sure ever view which can be set to opaque has its property set to YES. That for sure helps the system render the cell (including the backgound view if you use one.)
EDIT:
So you provided information that included UITableViews may the root problem. So two suggestions:
1) Can you step back and figure out how to make the scrollView a single UITableView? With table headers and footers, and section headers and footers, and even the ability to essentially make a cell a floating view, can't you figure out how to rearchitect what you have?
2) So you decide no to suggestion 1. Then, do this. Think of the space used by the tableview as being a container view. Whenever the tableview is edited, take an image snapshot of it and keep this image around. As soon as the user starts to scroll, swap the tableViews out for the images. When the scrollView stops swap the UITableView back in. This of course will take some fine tuning. In fact, you could probably overlay an opaque image snapshot over the table (which will hide it and prevent it from being asked to draw itself) during scrolling.
the human eye sees at about 60 FPS, so that's why it's recommended, but 30 FPS will also appear very smooth, especially when a regular user is viewing it, as opposed to you trying to find as much to fix as possible. This is obviously dependent on how fast the scrolling goes, if the difference from frame to frame is a movement of a few pixels, 30 FPS will do just fine, but faster movement will require a higher FPS to appear smooth
There are a few things you can do in general to get better table view performance:
1) Switch to Loren Brichter's method of drawing UITableViewCell's (for lack of a better link: http://www.therefinedgeek.com.au/index.php/2010/12/21/fast-scrolling-uitableview-updates-for-ios-4-2/)
Basically, all his code does is render all your cell content as one opaque UIView, which UITableView (and CoreGraphics) can very quickly blast onto a UITableViewCell
If you don't want to do all your cell design in drawRect:, you can still use nibs, but:
Make sure every subview is marked opaque
Don't have any transparent/semi-transparent subviews
Don't have any images with an alpha channel != 1.0f.
2) Don't let UIImageView do any scaling to display your image, give it a correctly-sized UIImage
3) If you're using iOS 5 and above, you can register a nib for a particular cell identifier. That way, when you call [tableView dequeueReusableCellWithIdentifier:], you are guaranteed to get a cell. Cell allocation is faster (according to Apple), and you get to write less code:
- (void)viewDidLoad {
UINib *nib = [UINib nibWithNibName:#"MyCell" bundle:nil];
[self.tableView registerNib:nib forCellReuseIdentifier:#"MyCellIdentifier"];
}
// ...
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *cellIdentifier = #"MyCellIdentifier";
MyCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
// Commented out code is no longer needed
//if (cell == nil) {
// cell = [[MyCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
//}
// setup cell
return cell;
}
4) Displaying images downloaded from the web
Display a default image (something to look at while the real image is downloading)
Start the download on a separate thread (hint: use GCD's dispatch_async())
When the image comes in, cache it (hint: NSCache), and display it on the cell
Do all image downloading/caching off the main thread; the only thing you should be doing on the main thread is setting the image (remember UI code HAS to be on the main thread!)
You'll probably want to write an async-capable UIImageView (or use an existing library).
Stay away from EGOImageView, even though it has async downloading, it does cache lookup (which happens to be on disk, so that means costly disk IO) on the main thread before dispatching to a background thread for the download. I used to use it, but I ended up writing my own set of classes to handle this, and it's significantly faster.
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Just follow these, and stuff other ppl have written here, and you'll have table views that scroll like glass in no time :)
You want 60fps, but 30 fps doesn't look too terrible in actuality. But I would try to achieve 60fps for a smoother look while scrolling.
There are many Performance Improvement possibilities, that are also shown by various tutorials
While 60 FPS is the ideal, games like Halo run very prettily in 30 FPS. The battlefield chaos in Halo probably involve more surprising, rapid motion than most lists, even complex ones like yours!
I am putting about 100 UITextFields programmatically into a UIScrollView for an elaborate data entry app (don't ask....bletch) and I am finding that it is taking too long to generate all of these UITextFields... something like 4 seconds.
Is there a better or quicker way to programmatically make so many user interface objects?
For instance would it be wiser to load a Xib/Nib and try to modify it as needed?
Thanks.
Have you thought about just creating a couple of UITextFields and reusing them once they're offscreen just as the UITableView does with cells?
Ouch, 100 textfields as data entry are harsh. But i know the problem when the client insists on a very dumb idea.
Back to topic: The problem is not the actual generation of your UITextFields. It is the way cocoa touch handles views. Views are terribly slow. Your idea with nibs is even worse, because they are in fact even slower.
The only way to avoid that is to simply not draw (add) many views. Just add the views which are currently in the visible area of the scrollview and remove the others.
Cocoa touch has actually already a very good control for that, it is called UITableView. ;)
Apple created the dequeue/reuse pattern in the UITableView exactly due those reasons.
So my suggestions for you is to use a tableview instead of a scrollview with custom cells (to avoid separators, etc.) and dequeue/reuse these cell and fill them with UITextFields which you store inside an array somewhere.
my first idea is to write a timer and load them 1 by 1 (or more) in small steps so that the UI doesn't freeze (it will still take 4 sec but at least user can input into into the loaded text fields)
here is how to make a timer
My iphone application has a user form under UIViewController.
When I out of application (go to background mode) and start application again some of my UIView changes its positions and sizes. (These UIViews depend on keyboard position)
Definately somewhere is my fault.
I try to figure what is going on when application starts again from background and where the UIView changes can be done.
May be you can suggest any links to read.
Thank you.
The UIViewController's viewDidLoad and viewWillAppear methods get called every time the view is dumped from memory, something that commonly happens when the app goes into the background. Depending on your code, it's possible that you're storing some position data that's not getting cleared. If that's the case, you can either:
Change your code to better fit the Model-View-Controller pattern so that the positioning code and variables are all in the controller, and you appropriately clean things up in its 'viewWillDisappearandviewDidUnload` methods (the better way), or
Clear out whatever remnants are hanging around in your application delegate's applicationWillEnterBackground method.
I have a UITableView that contains several cells and some of them (the ones for files that are still uploading) have both an UIActivityIndicator and an UIProgressView. The ones for files that are finished use a different icon (instead of the activity indicator) and hide the progressview.
This table is using a NSFetchedResultsController as data source, so I get the updates on the data model and update the content.
Everything works just fine. The problem, however, is performance. Every time I call reloadData my UIActivityIndicators flicker, and it's not very smooth. Although I'm caching from the nib file, reloadData will have to calculate the new progress % for the ProgressView and I don't do anything with the ActivityIndicator other than hiding it if upload is complete.
Anybody ever tried something similar? Is there a workaround?
I was thinking about having an array of my progressview references and use that instead of calling reloadData.. not sure if this is the correct approach.
Thanks,
Fernando
When you call reloadData on the UITableView, all the cells of the table view are completely refreshed, re-assembled and redrawn. All the old ones are thrown away. This means that all the subviews of the UITableViewCells are removed and re-created too (including your UIActivityIndicator and UIProgressView). The refresh causes these views to flicker, or perhaps jump back to their start state. As there is no way of setting the frame of a UIActivityIndicator, your suggestion of restoring some progress value simply isn't possible.
Instead, perhaps you should try and engineer your "refresh" to not require a complete refresh of the table? For example, if you want to change the text of a UITextField within the view, you could simply access this text field and set the text property (no refresh is required). Or, if you want to hide your progress indicators, you could go into the appropriate object instances and set their property. You should design your app so that this is possible. Making changes this way avoids having to reload cells from scratch.
Besides the benefit of fixing your problem, using this method of updating, you should also see a large performance increase. reloadData is a very costly method to use and should be only used if it is absolutely necessary to really re-create the entire UITableView from scratch.
Hope this helps. :)
I need to represent a linear process (think wizard) in an iPad app.
In principle I could use a UINavigationController and just keep pushing new controllers for each step of the process. But this seems rather inefficient since the process I'm modeling has no notion of navigating backwards so all previous views would pointlessly stay around and use up resources.
At the moment I keep adding and removing a subview to one "master" viewcontroller and basically swapping out the contents. This works but feels rather clunky and I hope there is some nicer way to achieve this.
Additionally there needs to be an animated transition between the views. (I have this working at the moment via beginAnimations / commitAnimations)
UPDATE:
To clarify my question: I'm aware that wizards usually have a back button. That's not what I'm building here.
The process that has to be shown possibly has a lot of steps (up to around 30-40 in some cases probably) so I really don't want to have 39 obsolete view controllers taking up ram.
Could you set the backBarButtonItem of each view controller's navigationItem to nil so that you don't show a back button?
You can extend uinavigationcontrollerdelegate and check every push event the current stack size. Then you can replace with a new reduced array that contains only the desired view controllers. By the way, if you implement a good memory management and release every resource on viewDidDisappear, i'm quite sure that it's not a matter for the os to manage a huge number of "empty" view controllers.
Hope it helps