iOS - 自定义转场动画

自iOS7开始，苹果支持自定义转场动画；
完整Demo：HHTransitionAnimator

若需自定义A控制器到B控制器的转场动画，则实现步骤如下：

• 第一步：自定义对象HHTransitionAnimator，自定义转场动画

@interface HHTransitionAnimator : UIPercentDrivenInteractiveTransition <UIViewControllerAnimatedTransitioning, UIViewControllerTransitioningDelegate>

@end

@implementation HHTransitionAnimator


 /** 转场动画时长 */
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
{
    return 0.3;
}

 /** 转场动画具体实现 - 这里是一个渐变效果 */
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
{
   UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    [[transitionContext containerView] addSubview:toView];
    toView.alpha = 0;
    [UIView animateWithDuration:weakSelf.transitionDuration animations:^{
      toView.alpha = 1;
    }completion:^(BOOL finished) {
      [transitionContext completeTransition:YES];
    }];
}

#pragma mark - UIViewControllerTransitioningDelegate
/** 自定义present动画 */
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
{
    return self;
}
@end

• 第二步：使用自定义转场动画

// A present -> B

@interface ListViewController : UIViewController

@property (nonatomic, strong) HHTransitionAnimator *animator; 

...

- (void)onClick
{
    UIViewController *vc = [UIViewController new];
    vc.transitioningDelegate = self.animator; //指定负责转场动画的对象
    vc.modalPresentationStyle = UIModalPresentationCustom;
    [self presentViewController:vc animated:YES completion:nil];
}
@end

至此，一个简单的自定义present转场动画就做好了，当然还有自定义dismiss动画，手势驱动返回，我们一一道来：

• 自定义dismiss动画
  1.实现animationControllerForDismissedController代理方法，返回负责dismiss动画的对象，这里返回自己
  2.又因为present和dismiss动画都会来这里：animateTransition:，所以搞个transitionType加以区分，修改后的代码如下

@implementation HHTransitionAnimator

...

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
{
    if(self.transitionType == HHViewControllerTransitionTypeDismiss){
        //dismiss动画
    }else{
      //present动画
    }
}

- (id<UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
{
    self.transitionType = HHViewControllerTransitionTypePresent;
    return self;
}
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
{
    self.transitionType = HHViewControllerTransitionTypeDismiss;
    return self;
}

• 手势驱动返回，这里简单实现一个左滑返回效果
  1.相信细心的同学已经发现了，我们自定义的HHTransitionAnimator是继承自UIPercentDrivenInteractiveTransition的，通过继承这个类，可以方便地根据滑动距离来控制dismiss动画完成的比例
  2.给需要滑动返回的控制器view添加手势，根据手势滑动距离更新dismiss动画比例
  3.实现interactionControllerForDismissal代理方法：当处于滑动返回状态时才返回自己，否则返回nil；
  4.用interacting属性来标识是否处于滑动返回中

- (void)addGestureToViewController:(UIViewController *)vc
{
    UIScreenEdgePanGestureRecognizer *ges = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)];
    ges.edges = UIRectEdgeLeft;
    [vc.view addGestureRecognizer:ges];
}
- (void)handleGesture:(UIScreenEdgePanGestureRecognizer *)ges
{
    CGFloat progress = [ges translationInView:ges.view].x / ges.view.bounds.size.width;
    
    switch (ges.state) {
        case UIGestureRecognizerStateBegan:
        {
            self.interacting = YES;
            [self.gestureVC dismissViewControllerAnimated:YES completion:nil];
        }
            break;
        case UIGestureRecognizerStateChanged:
        {
            [self updateInteractiveTransition:progress]; //更新页面返回进度
        }
            break;
        case UIGestureRecognizerStateEnded:
        {
            self.interacting = NO;
            if (progress < 0.3) {
                [self cancelInteractiveTransition];  //滑动距离过短，取消页面返回
            }else{
                [self finishInteractiveTransition];  //达到滑动返回距离，继续执行页面返回动画
            }
        }
            break;
        default: break;
    }
}

#pragma mark - UIViewControllerTransitioningDelegate
- (id<UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id<UIViewControllerAnimatedTransitioning>)animator;
{
    return self.interacting ? self : nil;
}

@end

最后，封装一下方便使用：

@interface UIViewController (HHTransitionAnimator)

- (void)hh_presentViewController:(UIViewController *)vc animated:(BOOL)flag TransitionAnimator:(HHTransitionAnimator *)animator completion:(void (^ __nullable)(void))completion;

@end

@implementation UIViewController (HHTransitionAnimator)

- (void)hh_presentViewController:(UIViewController *)vc animated:(BOOL)flag TransitionAnimator:(HHTransitionAnimator *)animator completion:(void (^ __nullable)(void))completion;
{
    self.hh_transitionAnimator = animator;
    self.hh_transitionAnimator.gestureVC = vc;
    vc.transitioningDelegate = self.hh_transitionAnimator;
    vc.modalPresentationStyle = UIModalPresentationCustom;
    dispatch_async(dispatch_get_main_queue(), ^{
        [self presentViewController:vc animated:flag completion:completion];
    });
}


#pragma mark - getter & setter
- (void)setHh_transitionAnimator:(HHTransitionAnimator *)hh_transitionAnimator
{
    objc_setAssociatedObject(self, @selector(hh_transitionAnimator), hh_transitionAnimator, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (HHTransitionAnimator *)hh_transitionAnimator
{
    return objc_getAssociatedObject(self, @selector(hh_transitionAnimator));
}

@end

使用的时候只需要调用
- (void)hh_presentViewController:animated:TransitionAnimator:completion:方法即可