I have an OpenGL animation drawing on the main window fired by an NSTimer. If I bring up a popover window with a scrollable UITableView menu, the animation freezes while scrolling is in process. Once the scrolling animation stops, the timer callbacks start again. Its only when the user actively tries to scroll that the main window stops updating.
It seems like Apple's scroll animation is somehow blocking dispatch on the main loop. Is this true and is there a way to fix it?
I dont really want to introduce multithreading if I can help it because that will exponentially increase the complexity of my code.
Also I tried using CADisplayLink instead of NSTimer and the display link calls are also blocked by the scrolling animation.
As answered by bdesham, "Apple’s #1 priority is UI responsiveness, and so in situations like this, UI actions will block other parts of your code. You need to move your timer to another thread."
NSTimer are tied to a run loop and mode. During event tracking, the mode is UITrackingRunLoopMode. By default, timers created by scheduledTimerWithTimeInterval are added with NSDefaultRunLoopMode and so do not fire during tracking.
[[NSRunLoop currentRunLoop] addTimer:yourTimer forMode:UITrackingRunLoopMode];
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So I'm making a simple trivia game and I have a timerView that shrinks as time passes. When the user selects an answer, it needs to stop shrinking immediately - it must be very responsive. I give the user 10 seconds per question. Originally I would animate 10 times (with a duration of 1.0f), calling the next "segment" of animation in the completion block of the previous animation. In the completion block I would check to see if the user has tapped an answer, and if so I don't continue the chain. That solution works fine except that it's not very responsive because it's on a per second basis-- user taps an answer at the start of the second segment and the bar has a noticeable continuation.
My solution to THAT problem was to instead have 1000 animation calls with a duration of 0.01f. After doing that, the responsiveness was on point - the view stops animating as soon as I tap an answer -- the issue though, is that it's not actually 10 seconds, it takes more like 20.
So question number 1: what's the smallest time interval animateWithDuration can actually process properly?
Question number 2: is there a better way to accomplish what I'm trying to do accomplish?
ill answer question two: yes there definitely is a better way, have a look at CADisplayLink
use it to shrink your view a little bit each frame, and end the display link when you need to
the most responsive way is: the user taps an answer, you response in the touch callback, remove animations. you can remove animations by CALayer's removeAllAnimations method
Another way to do it is to set the view to shrinking using a single animation with linear timing, and then set the speed of the view's layer to 0 to pause the animation. When you set the speed on the layer to 0 the animation pauses instantly.
This works because under the covers, UIView animation actually creates and installs CAAnimation objects on the view's layers. It's possible to pause and continue an in-flight UIView animation just like you can a CAAnimation.
I have a project called KeyframeViewAnimations (link) on github that allows you to pause, continue, or "scrub" UIView and CAAnimations back and forth with a slider. You could use that technique. The tricky bit will be figuring out how far along the animation is.
I have added an NSTimer which updates my interface, mainly labels with information 10 times every second. It calls a function which dispatches the work back to the main thread.
The view controller also has a scroll view. I have a paging system where I animate my scroll view's moving from page to page as a user taps on the tab (a button) which corresponds to each tab. That scrolling animation has just stopped happening - it is as if I am calling scrollToRect with animation as NO, even though I am calling it with YES.
I think that because I am updating my labels, auto layout is doing something dodgy in the background and ruining my scroll view animations. The same is happening for other animations which are using layout constraints to move views.
I know there are issues with Autolayout and NSTimer.
What can I do to fix this?
Thanks
I would create a boolean flag that inhibits the updates from the timer method. Set this to true just before you begin the animations and false once the animation completes. You probably also want to update the data 'manually' once the animation completes to capture any blocked updates.
I have weird problem while UITableView is scrolling I'm not able to invoke any events (touch down button, change layout colour). Funny thing is that when I touches on UISeachBar, the keyboard appears immediately.
I realize that main thread has been blocked, however I wonder is there any solution to fix this problem.
With the short description of your problem, I suppose that it is because when you scroll your tableView run loop change from NSDefaultRunLoopMode to NSEventTrackingRunLoopMode (see Run loops)
To change your UI while scrolling, the solution seems to perform your UI updates on the NSRunLoopCommonModes which includes the two loop mode you target.
Be prevent that it could make your tableview scrolling clunky.
I'm using a horizontal UIScrollView that displays photos on the first half of the screen. (Imagine a CGRect (0,0,320,120). The first scrollView is embedded in a second scrollview, which takes all the screen. When I scroll down the page (thus the second scrollView), the first scrollview stop being animated. I programmed a NSTimer to change photo every 3 seconds in the first UIScrollView, but while I'm scrolling the second scrollView, it seems like the animations are being queued. When I release my finger of the screen, there are few photo transitions (i.e: 2 changes if I scrolled without stoping for 6 seconds). In short: how can I make use of blocks (or something else) to continue my animations while I'm scrolling the second scrollView?
My NSTimer (in viewDidLoad):
timer = [NSTimer scheduledTimerWithTimeInterval:3.0 target:self selector:#selector(changePage:) userInfo:nil repeats:YES];
Your iOS app has a run loop that continually checks for things like user input. If it is busy detecting touch events, things that are scheduled on that run loop will not get performed. (Similarly, if you block the main thread with e.g. a big server request, you won't get touch events during that time).
Here's how you can get the NSTimer on the right run loop:
First, use timerWithTimeInterval:target:selector:userInfo:repeats: to create a timer not scheduled on a run loop.
Second, use - (void)addTimer:(NSTimer *)aTimer forMode:(NSString *)mode to schedule the timer on a run loop. For the mode argument (the run loop type), use NSRunLoopCommonModes to allow the timer to fire without having to wait on the main run loop.
Note that this same effect exists for e.g. performSelectorAfterDelay if done in the main run loop. It also applies to animation completion blocks. I'm not sure if there's an easy way around the animation completion block problem besides using CoreAnimation.
My app consists of an animation of about 25 frames. The animations is triggered by a button, and all is working. However, upon first invoking the animation, there is a few second delay.
I am aware that this is because the images need to be cached upon their first run in an animation, and I have ~2mb to be cached.
I wish Apple would implement an [animation prepareToPlay] method for this reason.
In the meantime, I'm running the animation within viewDidLoad. This caches the images during the splash screen, but then displays the animation.
There are two alternatives that I would like to consider.
This first is to forcibly cache the images upon initialization during the splash screen, without the animation playing upon loading the view. (read: custom UIImageView prepareToPlay method) --- This solution would be ideal.
The second alternative would be to keep my current code, running the animation at start-up once the view has been loaded, but disabling the invoking button until this first animation completes. Since UIImageView doesn't have it's own completion notification, would the best solution be to set up a timer equal to the animation duration and enable the button and the end of said timer?
Thanks in advance,
Greg
TL;DR --- How to forcibly cache animation images upon initialization.
I also faced problem as yours. I had created my own question here, and I got good answers. Check it out here: Does UIImageView cache images?
Good luck!