Infinite animation not being interrupted by home button - iphone

Question

I have several objects of a subclass of uiview, inside the main view of a viewcontroller that I animate infinitely by calling the following method in the class:
- (void)hover:(NSNumber *)upDown {
int sense = [upDown intValue];
[UIView animateWithDuration:0.8 delay:0.1 options:UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionAllowUserInteraction
animations:^{
CGRect frame = self.frame;
frame.origin.y += (sense==1?1:-1) * 5;
self.frame = frame;
}
completion:^(BOOL finished){
[self hover:[NSNumber numberWithInt:(sense==1?0:1)]];
}];
}
It works great except that in the device, when the home button is pressed, the app semi-freezes (the app eventually goes to background by pressing the home button repeatedly for quite a while) and any interaction with other buttons stops working. It works fine in any other case, i.e. as long as I don't press the home button I can navigate through controllers, press buttons, etc... and on the simulator.
Any ideas?
UPDATE: The culprit seems to be the shadow I'm applying to the views I'm animating
self.layer.shadowColor = [UIColor blackColor].CGColor;
self.layer.shadowOpacity = 1.0;
self.layer.shadowRadius = 5.0;
This seems to be causing some kind of overhead that only affects the app not being able to go into background state???
Anyone encountered this?
UPDATE: In the end I decided to get rid of that code and draw the shadow with Quartz in the drawRect: method. I suspect the problem might have to do with the snapshot that the iPhone takes before going into background mode and the shadow applied to the layer outside the bounds, but it's just a guess.

Answer 1

Basically the problem has to do with this way of obtaining a rounded shape and shadow:
[self.layer setCornerRadius:radius];
self.layer.shadowColor = [UIColor blackColor].CGColor;
self.layer.shadowOpacity = 0.2;
self.layer.shadowRadius = 5;
self.layer.shadowOffset = CGSizeMake(0, 10);
The shadow draws outside the frame of the view and the iPhone's process of going into background state doesn't seem to like that when animating.
As I mention in the update, I got rid of this and used Quartz to draw both shape an shadow inside the frame. There are many posts on how to do this but here it goes anyway:
-(void)drawRect:(CGRect)rect
{
const CGFloat *cComps = CGColorGetComponents([UIColor blackColor]).CGColor;
CGContextRef context = UIGraphicsGetCurrentContext();
CGFloat center = rect.size.width / 2.0;
CGFloat radius = center;
CGContextBeginPath(context);
CGContextSetShadowWithColor(context, CGSizeMake(0, 10), 4, [UIColor colorWithWhite:0 alpha:0.1].CGColor);
CGContextAddArc(context, center, center, radius, 0, 2*M_PI, 1);
CGContextSetRGBFillColor(context, cComps[0], cComps[1], cComps[2], 1.0);
CGContextFillPath(context);
}
NOTE: I set the height of the view to +15px to accommodate the shadow at the bottom.
Hope it helps somebody. It certainly drove me mad for a couple of days...

Answer 2

I recently ran into this problem and this post was incredibly helpful in identifying the culprit. Turns out though, that simply setting shouldRasterize on the shadowed layers is sufficient to prevent the freeze. (You should also set rasterizationScale to be the same as the device's main screen's scale.)
All of my shadowed layers were relatively static and weren't being constantly animated, so YMMV.
Your standard shadow adding code:
layer.shadowColor = [UIColor blackColor].CGColor;
layer.shadowOffset = CGSizeMake(0, 1);
layer.shadowOpacity = 0.5;
layer.shadowRadius = 1.0;
This is what you need to add:
layer.rasterizationScale = [[UIScreen mainScreen] scale];
layer.shouldRasterize = YES;

Answer 3

My first thought is that you should implement a BOOL in your .h file (let's call it stopGoing). Then do the following:
- (void)hover:(NSNumber *)upDown {
if(!stopGoing){
int sense = [upDown intValue];
[UIView animateWithDuration:0.8 delay:0.1 options:UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionAllowUserInteraction
animations:^{
CGRect frame = self.frame;
frame.origin.y += (sense==1?1:-1) * 5;
self.frame = frame;
}
completion:^(BOOL finished){
[self hover:[NSNumber numberWithInt:(sense==1?0:1)]];
}];
} else {
// do something else
}
}
Then, in your IBAction that you have linked to the button, just do this:
-(IBAction)myButton:(id)sender{
stopGoing = YES;
}
That should effectively stop the loop, without being too invasive.