Synchronising image, text, and positioning with CoreAnimation - ios

Question

I am a bit of a beginner with animations and have been experimenting with CoreAnimation for a couple of days. Feel free to warn me if this question does not make sense, but I'm trying to achieve the following. I have three objects:
one should be an image, moving according to a given pattern
one should be an UIImage that swaps two images
one should be a text (CATextLayer?) whose content changes
The three actions should happen in sync.
As an example, think about a programme showing a sinusoid function, like in a ECG, oscillating between -1 and +1: the first image would then move according to the current value (-1, -0.9, -0.8, ... 0, +0.1, +0.2, ... 1), the swap image would show "+" for positive values and "-" for negative values, and the text would alternate between "Positive" and "Negative".
I've tried with CAAnimationGroup but I'm clearly missing something. Some code:
{
// image that moves
CALayer *img1 = [CALayer layer];
img1.bounds = CGRectMake(0, 0, 20, 20);
img1.position = CGPointMake(x1,y1);
UIImage *img1Image = [UIImage imageNamed:#"image.png"];
img1.contents = (id)img1Image.CGImage;
// image that changes
CALayer *swap = [CALayer layer];
swap.bounds = CGRectMake(0, 0, 30, 30);
swap.position = CGPointMake(x2,y2);
NSString* nameswap = #"img_swap_1.png"
UIImage *swapImg = [UIImage imageNamed:nameswap];
// text
CATextLayer *text = [CATextLayer layer];
text.bounds = CGRectMake(0, 0, 100, 100);
text.position = CGPointMake(x3,y3);
text.string = #"Text";
// create animations
CGFloat duration = 0.2;
CGFloat totalDuration = 0.0;
CGFloat start = 0;
NSMutableArray* animarray = [[NSMutableArray alloc] init];
NSMutableArray* swapanimarray = [[NSMutableArray alloc] init];
NSMutableArray* textanimarray = [[NSMutableArray alloc] init];
float prev_x = 0;
float prev_y = 0;
// I get my values for moving the object
for (NSDictionary* event in self.events) {
float actual_x = [[event valueForKey:#"x"] floatValue];
float actual_y = [[event valueForKey:#"y"] floatValue];
// image move animation
CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:#"position"];
CGPoint startPt = CGPointMake(prev_x,prev_y);
CGPoint endPt = CGPointMake(actual_x, actual_y);
anim.duration = duration;
anim.fromValue = [NSValue valueWithCGPoint:startPt];
anim.toValue = [NSValue valueWithCGPoint:endPt];
anim.beginTime = start;
anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
[animarray addObject:anim];
// image swap animation
CABasicAnimation *swapanim = [CABasicAnimation animationWithKeyPath:#"contents"];
swapanim.duration = duration;
swapanim.beginTime = start;
NSString* swapnamefrom = [NSString stringWithFormat:#"%#.png", prev_name];
NSString* swapnameto = [NSString stringWithFormat:#"%#.png", current_name];
UIImage *swapFromImage = [UIImage imageNamed:swapnamefrom];
UIImage *swapToImage = [UIImage imageNamed:swapnameto];
swapanim.fromValue = (id)(swapFromImage.CGImage);
swapanim.toValue = (id)(swapToImage.CGImage);
swapanim.fillMode = kCAFillModeForwards;
swapanim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
[swapanimarray addObject:swapanim];
//text animation
CABasicAnimation *textanim = [CABasicAnimation animationWithKeyPath:#"contents"];
textanim.duration = duration;
textanim.fromValue = #"Hey";
textanim.toValue = #"Hello";
textanim.beginTime = start;
[textanimarray addObject:textanim];
// final time settings
prev_x = actual_x;
prev_y = actual_y;
start = start + duration;
totalDuration = start + duration;
}
}
CAAnimationGroup* group = [CAAnimationGroup animation];
[group setDuration:totalDuration];
group.removedOnCompletion = NO;
group.fillMode = kCAFillModeForwards;
[group setAnimations:animarray];
CAAnimationGroup* swapgroup = [CAAnimationGroup animation];
[swapgroup setDuration:totalDuration];
swapgroup.removedOnCompletion = NO;
swapgroup.fillMode = kCAFillModeForwards;
[swapgroup setAnimations:swapanimarray];
CAAnimationGroup* textgroup = [CAAnimationGroup animation];
[textgroup setDuration:totalDuration];
textgroup.removedOnCompletion = NO;
textgroup.fillMode = kCAFillModeForwards;
[textgroup setAnimations:textanimarray];
[ball addAnimation:group forKey:#"position"];
[swap addAnimation:flaggroup forKey:#"position"];
[text addAnimation:textgroup forKey:#"contents"];
[self.layer addSublayer:ball];
[self.layer addSublayer:swap];
[self.layer addSublayer:text];
}
Now... the problems:
1) the swap image reverts to the original at every swap. So, if I swap A->B, I see it going from A to B in the expected duration time, but then reverting to A. I've read a number of threads on SO about this but couldn't get it to work.
2) changing the string of the text layer in a timed fashion... is this possible with this infrastructure? Basically, I'm trying to get the text and the swap image to change as soon as the first image moves, as described in the example.
3) setting the delegate for the CABasicAnimation doesn't have any effect, although it does for the CAAnimationGroup: as a result, you can't manage events like animationDidStop for every single animation, just for the whole group. Is there any alternative way to do so?
4) following from 3), is it possible, using CAAnimationGroup, to intercept the events to create a stop/start behaviour? Let's suppose I wanted to have play/stop buttons, and to resume the animation from exactly where I had left it?
As a conclusive question, I would simply like to know if anyone did something similar and, most importantly, if this way of doing things (using a CAAnimationGroup) is actually the way to go or if it's better to use CAKeyFrameAnimation or something else.

Answer 1

I managed to solve the problem, albeit with some workarounds.
1) The trick here is that
removedOnCompletion = NO;
fillMode = kCAFillModeForwards;
need to be assigned to every single animation, not to the CAAnimationGroup.
2) This requires a separate animation to be determined for the CATextLayer, and animating the "string" property. In this case, the code was right except for the "contents" key-value which should have been
[text addAnimation:textgroup forKey:#"contentAnimate"];
Alternatively, see point 3. The callback way of operation allows to change a label.text.
3) The only way to do this is to actually not use the CAAnimationGroup and set up a sequence of CABasicAnimation. The general schema is: create the first CABasicAnimation in a function, assign the delegate. In the animationDidStop method, add a callback to the function that creates the CABasicAnimation. This way, each animation will be created. At the same time, this allows to intercept and react to specific events within the animation.
-(void)performNextAnimation:(int)index {
// ... this gives for granted you have an object for #index ...
NSDictionary* thisEvent = [self.events objectAtIndex:index];
float prev_x = [thisEvent valueForKey:#"prev_x"];
float prev_y = [thisEvent valueForKey:#"prev_x"];
float actual_x = [thisEvent valueForKey:#"prev_x"];
float actual_y = [thisEvent valueForKey:#"prev_x"];
CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:#"position"];
GPoint startPt = CGPointMake(prev_x,prev_y);
CGPoint endPt = CGPointMake(actual_x, actual_y);
anim.duration = 0.5;
anim.fromValue = [NSValue valueWithCGPoint:startPt];
anim.toValue = [NSValue valueWithCGPoint:endPt];
anim.beginTime = start;
[anim setDelegate:self];
anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
[object addAnimation:anim forKey:#"position"];
}
- (void)animationDidStop:(CAAnimation *)theAnimation finished:(BOOL)flag {
// ... your conditions go here ...
// ... your actions go here ...
// e.g. set label.text
[self performNextAnimation];
}
4) Following from 3, this is not possible in CAAnimationGroup. Reading the docs, I would say that CAAnimationGroup is not intended to be used for sequences in which each event represents a step forward in time (for this you need to use CAKeyFrameAnimation or a sequence of CABasicAnimation with a callback function, as I did). CAAnimationGroup is intended for linked animation that should be executed on an all-or-nothing basis (similarly to CATransaction).