iOS: How to convert UIViewAnimationCurve to UIViewAnimationOptions?

Question

The UIKeyboardAnimationCurveUserInfoKey has a UIViewAnimationCurve value. How do I convert it to the corresponding UIViewAnimationOptions value for use with the options argument of +[UIView animateWithDuration:delay:options:animations:completion:]?

// UIView.h

typedef enum {
    UIViewAnimationCurveEaseInOut,         // slow at beginning and end
    UIViewAnimationCurveEaseIn,            // slow at beginning
    UIViewAnimationCurveEaseOut,           // slow at end
    UIViewAnimationCurveLinear
} UIViewAnimationCurve;

// ...

enum {
    // ...
    UIViewAnimationOptionCurveEaseInOut            = 0 << 16, // default
    UIViewAnimationOptionCurveEaseIn               = 1 << 16,
    UIViewAnimationOptionCurveEaseOut              = 2 << 16,
    UIViewAnimationOptionCurveLinear               = 3 << 16,
    // ...
};
typedef NSUInteger UIViewAnimationOptions;

Obviously, I could create a simple category method with a switch statement, like so:

// UIView+AnimationOptionsWithCurve.h

@interface UIView (AnimationOptionsWithCurve)
@end

// UIView+AnimationOptionsWithCurve.m

@implementation UIView (AnimationOptionsWithCurve)

+ (UIViewAnimationOptions)animationOptionsWithCurve:(UIViewAnimationCurve)curve {
    switch (curve) {
        case UIViewAnimationCurveEaseInOut:
            return UIViewAnimationOptionCurveEaseInOut;
        case UIViewAnimationCurveEaseIn:
            return UIViewAnimationOptionCurveEaseIn;
        case UIViewAnimationCurveEaseOut:
            return UIViewAnimationOptionCurveEaseOut;
        case UIViewAnimationCurveLinear:
            return UIViewAnimationOptionCurveLinear;
    }
}

@end

But, is there an even easier/better way?

Answer 1

The category method you suggest is the “right” way to do it—you don’t necessarily have a guarantee of those constants keeping their value. From looking at how they’re defined, though, it seems you could just do

animationOption = animationCurve << 16;

...possibly with a cast to NSUInteger and then to UIViewAnimationOptions, if the compiler feels like complaining about that.

Answer 2

Arguably you can take your first solution and make it an inline function to save yourself the stack push. It's such a tight conditional (constant-bound, etc) that it should compile into a pretty tiny piece of assembly.

Edit: Per @matt, here you go (Objective-C):

static inline UIViewAnimationOptions animationOptionsWithCurve(UIViewAnimationCurve curve)
{
  switch (curve) {
    case UIViewAnimationCurveEaseInOut:
        return UIViewAnimationOptionCurveEaseInOut;
    case UIViewAnimationCurveEaseIn:
        return UIViewAnimationOptionCurveEaseIn;
    case UIViewAnimationCurveEaseOut:
        return UIViewAnimationOptionCurveEaseOut;
    case UIViewAnimationCurveLinear:
        return UIViewAnimationOptionCurveLinear;
  }
}

Swift 3:

extension UIViewAnimationOptions {
    init(curve: UIViewAnimationCurve) {
        switch curve {
            case .easeIn:
                self = .curveEaseIn
            case .easeOut:
                self = .curveEaseOut
            case .easeInOut:
                self = .curveEaseInOut
            case .linear:
                self = .curveLinear
        }
    }
}

Answer 3

In Swift you can do

extension UIViewAnimationCurve {
    func toOptions() -> UIViewAnimationOptions {
        return UIViewAnimationOptions(rawValue: UInt(rawValue << 16))
    }
}