iOS-自定义交互式转场动画

// 该方法返回导航跳转时的动画，如果返回nil，则是系统默认的跳转动画，并且通过operation来判断当前执行push还是pop
-(id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
    return nil;
}

// 该方法返回自定义交互动画，只有实现该协议，才能在跳转时实现与用户交互
-(id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
{
    return nil;
}

// 该方法返回动画执行的时间，transitionContext由系统获取
-(NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext
{
    return 0.3;
}

// 通过该协议，获取跳转的两个VC
-(void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    [self animateTransition:transitionContext fromVC:fromVC toVC:toVC fromView:fromVC.view toView:toVC.view];
}

// 这是模仿系统导航跳转的例子
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext fromVC:(UIViewController *)fromVC toVC:(UIViewController *)toVC fromView:(UIView *)fromView toView:(UIView *)toView{
    [[transitionContext containerView] addSubview:toView];
    if (_isPush) {
        [[transitionContext containerView] bringSubviewToFront:toView];
        toView.transform = CGAffineTransformMakeTranslation(-toView.bounds.size.width, 0);
    }
    else{
        [[transitionContext containerView] bringSubviewToFront:fromView];
    }
    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        if (_isPush) {
            toView.transform = CGAffineTransformIdentity;
        }
        else{
            fromView.transform = CGAffineTransformMakeTranslation(-fromView.bounds.size.width, 0);
        }
    } completion:^(BOOL finished) {
        transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}

// 在view上加入pan手势
UIPanGestureRecognizer *gesture = objc_getAssociatedObject(self.interactiveVC.view, (__bridge const void *)(kpanGestureKey));
    if (gesture) {
        [self.interactiveVC.view removeGestureRecognizer:gesture];
    }
    gesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanGesture:)];
    [self.interactiveVC.view addGestureRecognizer:gesture];
    objc_setAssociatedObject(self.interactiveVC.view, (__bridge const void *)(kpanGestureKey), gesture,OBJC_ASSOCIATION_RETAIN_NONATOMIC);

// 当pan手势移动，通过移动的距离来计算当前跳转动画需要完成的百分比，当手势结束时，判断动画完成的百分比。如果>50%，finishInteractiveTransition完成跳转动画；如果<50%，cancelInteractiveTransition取消动画，返回原样
case UIGestureRecognizerStateChanged:
        CGFloat fraction = point.x / [[UIScreen mainScreen] bounds].size.width;
        fraction = fminf(fmaxf(fraction, 0.0), 1.0);
        self.shouldComplete = (fraction > 0.5);
        [self updateInteractiveTransition:fraction];
    break;
case UIGestureRecognizerStateEnded:
case UIGestureRecognizerStateCancelled:
        self.interactioning = NO;
        if (!self.shouldComplete || pan.state == UIGestureRecognizerStateCancelled) {
            [self cancelInteractiveTransition];
        }
        else {
            [self finishInteractiveTransition];
        }
    break;