iOS 7 的 MotionEffects

iOS 7 剛出來時，大家第一個會注意到的事在 Lock Screen 有一個會動的背景；那就是 Motion Effects。
其實它很簡單，我試著在一個UIView 加上一個 UIButton，接著讓 Button 是浮動的。看程式碼就懂了。

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    aButton.layer.mask.frame = aButton.bounds;
    aButton.layer.masksToBounds = YES;

    UIInterpolatingMotionEffect *xAxis = [[UIInterpolatingMotionEffect alloc]
                                          initWithKeyPath:@"center.x"
                                          type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];

    xAxis.minimumRelativeValue = [NSNumber numberWithFloat:-90.0];
    xAxis.maximumRelativeValue = [NSNumber numberWithFloat:90.0];

    UIInterpolatingMotionEffect *yAxis = [[UIInterpolatingMotionEffect alloc]
                                          initWithKeyPath:@"center.y"
                                          type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];

    yAxis.minimumRelativeValue = [NSNumber numberWithFloat:-90.0];
    yAxis.maximumRelativeValue = [NSNumber numberWithFloat:90.0];

    UIMotionEffectGroup *group = [[UIMotionEffectGroup alloc]init];
    group.motionEffects = @[xAxis, yAxis];
    [aButton addMotionEffect:group];
}