objective c - iOS 7 parallax effect in my view controller

Question

I'm developing an app for iOS 7 in Objective-C. I've got a screen in my app with a few buttons and a pretty background image. (It's a simple xib with UIButtons on top of a UIImageView.)

I was thinking that it'd be cool if those buttons had the parallax effect that the iOS 7 home screen has, so if you tilt the phone you could see the background.

How can I implement that effect in my own app?

Answer 1

With iOS 7, Apple introduced UIMotionEffect to add Motion effects that are related to the orientation of the user’s device. For example, to emulate the parallax effect on the home screen, you can use the subclass UIInterpolatingMotionEffect, as explained here, just with a few lines of code.

Objective-C:

// Set vertical effect
UIInterpolatingMotionEffect *verticalMotionEffect = 
  [[UIInterpolatingMotionEffect alloc] 
  initWithKeyPath:@"center.y"
             type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
verticalMotionEffect.minimumRelativeValue = @(-10);
verticalMotionEffect.maximumRelativeValue = @(10);

// Set horizontal effect 
UIInterpolatingMotionEffect *horizontalMotionEffect = 
  [[UIInterpolatingMotionEffect alloc] 
  initWithKeyPath:@"center.x"     
             type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
horizontalMotionEffect.minimumRelativeValue = @(-10);
horizontalMotionEffect.maximumRelativeValue = @(10);
  
// Create group to combine both
UIMotionEffectGroup *group = [UIMotionEffectGroup new];
group.motionEffects = @[horizontalMotionEffect, verticalMotionEffect];

// Add both effects to your view
[myBackgroundView addMotionEffect:group];

Swift (Thanks to @Lucas):

// Set vertical effect
let verticalMotionEffect = UIInterpolatingMotionEffect(keyPath: "center.y",
type: .TiltAlongVerticalAxis)
verticalMotionEffect.minimumRelativeValue = -10
verticalMotionEffect.maximumRelativeValue = 10

// Set horizontal effect
let horizontalMotionEffect = UIInterpolatingMotionEffect(keyPath: "center.x",
    type: .TiltAlongHorizontalAxis)
horizontalMotionEffect.minimumRelativeValue = -10
horizontalMotionEffect.maximumRelativeValue = 10

// Create group to combine both
let group = UIMotionEffectGroup()
group.motionEffects = [horizontalMotionEffect, verticalMotionEffect]

// Add both effects to your view
myBackgroundView.addMotionEffect(group)

Also, you can find a bunch of libraries to do this easier or to add this functionality to older iOS versions:

• NGAParallaxMotion (requires iOS 7).
• DVParallaxView (requires iOS 5.0 or higher and ARC).
• MKParallaxView (tested with iOS 6.0, requires ARC).
• UIView-MWParallax (tested with iOS 6.1, requires ARC).