UIInterpolatingMotionEffect works randomly - ios

Question

I'm adding a UIInterpolatingMotionEffect to some views in UITableViewCells this way:
UIInterpolatingMotionEffect *horizontalEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:#"center.x" type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
UIInterpolatingMotionEffect *verticalEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:#"center.y" type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
horizontalEffect.minimumRelativeValue = #(-horizontal);
horizontalEffect.maximumRelativeValue = #(horizontal);
verticalEffect.minimumRelativeValue = #(-vertical);
verticalEffect.maximumRelativeValue = #(vertical);
UIMotionEffectGroup *effectsGroup = [UIMotionEffectGroup new];
effectsGroup.motionEffects = #[horizontalEffect, verticalEffect];
[view addMotionEffect:effectsGroup];
The problem is that the effect only appears randomly, where some views get the effect and some don't. After pushing a view controller and going back, some others work and some others don't.
Is there something I'm missing? Should the effect be applied every time the cell is reused?

Answer 1

I had the same problem. I fixed it by forcing a redraw of all the cells - using reloadSections:withRowAnimation: will likely work for most people (or a similar method), although for me I ultimately had to write my own cell inits and reuse code that let me keep a reference to every created cell in a mutable array, and then clear that array and build from scratch when I chose to. Hope that helps.

Answer 2

UPDATE:
Had to completely remove my previous answer, because I have finally found a better solution.
It looks like iOS7/8 messes with the motion effects of the views inside the table/collection views once the cell is redrawn / dequeued. You need to make sure your motion effect are set up / updated after the cell is dequeued / set up.
To properly do so, you need to move your motion effect logic to the -layoutSubviews method.
Then just send the [self setNeedsLayout] message within your constructor and methods, which you use to update the cell contents after the cell is dequeued and updated.
This solved the issue completely for me.

Answer 3

Using a UICollectionView, I was experiencing the same problem. After pushing a new controller, then going back to the UICollectionView, some of my cells' UIInterpolatingMotionEffects stopped functioning, but were still listed on the view's motionEffects property.
Solution:
I called to setup my motion effects in -layoutSubviews, and whenever configuring the cell, I called -setNeedsLayout to ensure -layoutSubviews was called.
Additionally, every time I setup my motion effects, I would remove the previous motion effects. This was key.
Here's the method I called in -layoutSubviews:
- (void)applyInterpolatingMotionEffectToView:(UIView *)view withParallaxLimit:(CGFloat)limit
{
NSArray *effects = view.motionEffects;
for (UIMotionEffect *motionEffect in effects)
{
[view removeMotionEffect:motionEffect];
}
UIInterpolatingMotionEffect *effectX = [[UIInterpolatingMotionEffect alloc] initWithKeyPath: #"center.x" type: UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
effectX.minimumRelativeValue = #(-limit);
effectX.maximumRelativeValue = #(limit);
UIInterpolatingMotionEffect *effectY = [[UIInterpolatingMotionEffect alloc] initWithKeyPath: #"center.y" type: UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
effectY.minimumRelativeValue = #(-limit);
effectY.maximumRelativeValue = #(limit);
[view addMotionEffect: effectX];
[view addMotionEffect: effectY];
}
Hope it helps! Also, running on iOS 9.