iOS开发 — 转场动画详解

UIViewControllerAnimatedTransitioning:

负责present/dismiss的自然过程的动画效果

@protocol UIViewControllerAnimatedTransitioning <NSObject>
// This is used for percent driven interactive transitions, as well as for
// container controllers that have companion animations that might need to
// synchronize with the main animation.
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
// This method can only be a no-op if the transition is interactive and not a percentDriven interactive transition.
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@optional

/// A conforming object implements this method if the transition it creates can
/// be interrupted. For example, it could return an instance of a
/// UIViewPropertyAnimator. It is expected that this method will return the same
/// instance for the life of a transition.
- (id <UIViewImplicitlyAnimating>) interruptibleAnimatorForTransition:(id <UIViewControllerContextTransitioning>)transitionContext API_AVAILABLE(ios(10.0));

// This is a convenience and if implemented will be invoked by the system when the transition context's completeTransition: method is invoked.
- (void)animationEnded:(BOOL) transitionCompleted;

Example

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext{
    return 0.35;
}
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    UIView *containerView = transitionContext.containerView;
    
    // For a Presentation:
    //      fromView = The presenting view.
    //      toView   = The presented view.
    // For a Dismissal:
    //      fromView = The presented view.
    //      toView   = The presenting view.
    UIView *fromView;
    UIView *toView;
    
    // In iOS 8, the viewForKey: method was introduced to get views that the
    // animator manipulates.  This method should be preferred over accessing
    // the view of the fromViewController/toViewController directly.
    // It may return nil whenever the animator should not touch the view
    // (based on the presentation style of the incoming view controller).
    // It may also return a different view for the animator to animate.
    //
    // Imagine that you are implementing a presentation similar to form sheet.
    // In this case you would want to add some shadow or decoration around the
    // presented view controller's view. The animator will animate the
    // decoration view instead and the presented view controller's view will
    // be a child of the decoration view.
    if ([transitionContext respondsToSelector:@selector(viewForKey:)]) {
        fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
        toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    } else {
        fromView = fromViewController.view;
        toView = toViewController.view;
    }
    
    fromView.frame = [transitionContext initialFrameForViewController:fromViewController];
    toView.frame = [transitionContext finalFrameForViewController:toViewController];
    
    fromView.alpha = 1.0f;
    toView.alpha = 0.0f;
    
    // We are responsible for adding the incoming view to the containerView
    // for the presentation/dismissal.
    [containerView addSubview:toView];
    
    NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];
    
    [UIView animateWithDuration:transitionDuration animations:^{
        fromView.alpha = 0.0f;
        toView.alpha = 1.0;
    } completion:^(BOOL finished) {
        // When we complete, tell the transition context
        // passing along the BOOL that indicates whether the transition
        // finished or not.
        BOOL wasCancelled = [transitionContext transitionWasCancelled];
        [transitionContext completeTransition:!wasCancelled];
    }];
}

UIViewControllerInteractiveTransitioning

负责present/dismiss 交互式过程中的效果，一般可通过继承 UIPercentDrivenInteractiveTransition 去自定义

@interface UIPercentDrivenInteractiveTransition : NSObject <UIViewControllerInteractiveTransitioning>


/// Use this method to pause a running interruptible animator. This will ensure that all blocks
/// provided by a transition coordinator's notifyWhenInteractionChangesUsingBlock: method
/// are executed when a transition moves in and out of an interactive mode.
- (void)pauseInteractiveTransition API_AVAILABLE(ios(10.0));

// These methods should be called by the gesture recognizer or some other logic
// to drive the interaction. This style of interaction controller should only be
// used with an animator that implements a CA style transition in the animator's
// animateTransition: method. If this type of interaction controller is
// specified, the animateTransition: method must ensure to call the
// UIViewControllerTransitionParameters completeTransition: method. The other
// interactive methods on UIViewControllerContextTransitioning should NOT be
// called. If there is an interruptible animator, these methods will either scrub or continue 
// the transition in the forward or reverse directions.
- (void)updateInteractiveTransition:(CGFloat)percentComplete;
- (void)cancelInteractiveTransition;
- (void)finishInteractiveTransition;

@end

Example

- (CGFloat)percentForGesture:(UIScreenEdgePanGestureRecognizer *)gesture
{
    // Because view controllers will be sliding on and off screen as part
    // of the animation, we want to base our calculations in the coordinate
    // space of the view that will not be moving: the containerView of the
    // transition context.
    UIView *transitionContainerView = self.transitionContext.containerView;
    
    CGPoint locationInSourceView = [gesture locationInView:transitionContainerView];
    
    // Figure out what percentage we've gone.

    CGFloat width = CGRectGetWidth(transitionContainerView.bounds);
    CGFloat height = CGRectGetHeight(transitionContainerView.bounds);
    
    // Return an appropriate percentage based on which edge we're dragging
    // from.
    if (self.edge == UIRectEdgeRight)
        return (width - locationInSourceView.x) / width;
    else if (self.edge == UIRectEdgeLeft)
        return locationInSourceView.x / width;
    else if (self.edge == UIRectEdgeBottom)
        return (height - locationInSourceView.y) / height;
    else if (self.edge == UIRectEdgeTop)
        return locationInSourceView.y / height;
    else
        return 0.f;
}


//| ----------------------------------------------------------------------------
//! Action method for the gestureRecognizer.
//
- (IBAction)gestureRecognizeDidUpdate:(UIScreenEdgePanGestureRecognizer *)gestureRecognizer
{
    switch (gestureRecognizer.state)
    {
        case UIGestureRecognizerStateBegan:
            // The Began state is handled by the view controllers.  In response
            // to the gesture recognizer transitioning to this state, they
            // will trigger the presentation or dismissal.
            break;
        case UIGestureRecognizerStateChanged:
            // We have been dragging! Update the transition context accordingly.
            [self updateInteractiveTransition:[self percentForGesture:gestureRecognizer]];
            break;
        case UIGestureRecognizerStateEnded:
            // Dragging has finished.
            // Complete or cancel, depending on how far we've dragged.
            if ([self percentForGesture:gestureRecognizer] >= 0.5f)
                [self finishInteractiveTransition];
            else
                [self cancelInteractiveTransition];
            break;
        default:
            // Something happened. cancel the transition.
            [self cancelInteractiveTransition];
            break;
    }
}

UIViewControllerTransitioningDelegate

负责指定UIViewController的present/dismiss时的动画对象 （包括自然过程动画与交互过程动画），默认声明了该代理

@protocol UIViewControllerTransitioningDelegate <NSObject>

@optional
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed;

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(nullable UIViewController *)presenting sourceViewController:(UIViewController *)source API_AVAILABLE(ios(8.0));

@end

UIPresentationController

集成presentedViewController 和 presentingViewController，并提供很多转场相关的协议； 可继承后，用于自定义转场动画；

UINavigationControllerDelegate

导航控制器的代理，提供了转场动画自定义方法，类似UIViewControllerTransitioningDelegate

UITabBarControllerDelegate

Tab控制器的代理，提供了转场动画自定义方法