Transition 过渡/转场动画(一)

UIViewController 的转场效果

当viewController通过push 或 present 进行转场时, 系统自带的动画是从右侧push进来一个新的viewControler (或从下面present 一个新的ViewController),  接下来我们要做的就是要自定义系统的这个动画效果.

原理: 比如当viewController  调用 dismiss 后, 系统会检查当前 vc 是否实现<UIViewControllerTransitioningDelegate> 协议, 该协议会返回 自定义 的转场动画

例: 通过pan手势, dismiss 当前viewController

1. 在调用dimiss的 VC 中实现 <UIViewControllerTransitioningDelegate> 协议

#import "SecondViewController.h"
#import "CustomInteractiveTransition.h"
#import "CustomDissmissAnimation.h"

@interface SecondViewController () <UIViewControllerTransitioningDelegate>

@property (nonatomic, strong) CustomInteractiveTransition *interactiveAnimator;
@property (nonatomic, strong) CustomDissmissAnimation *dismissAnimator;

@end

@implementation SecondViewController

- (instancetype)init {
    if (self = [super init]) {
        self.transitioningDelegate = self;
    }
    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    self.view.backgroundColor = [UIColor cyanColor];

    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    [button setTitle:@"dismiss" forState:UIControlStateNormal];
    button.frame = CGRectMake(, , , );
    [button addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];

    self.interactiveAnimator = [[CustomInteractiveTransition alloc] initWithViewController:self];

    self.dismissAnimator = [[CustomDissmissAnimation alloc] init];

    UIPanGestureRecognizer *panGestureRecognizer =[[UIPanGestureRecognizer alloc] initWithTarget:self.interactiveAnimator action:@selector(panGestureAction:)];
    [self.view addGestureRecognizer:panGestureRecognizer];

    [self.transitionCoordinator notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {

    }];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [self.transitionCoordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
        UIView *view = [context viewForKey:UITransitionContextFromViewKey];
        view.transform = CGAffineTransformMakeScale(0.7, 0.7);

    } completion:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
//        UIView *view = [context viewForKey:UITransitionContextFromViewKey];
//        view.transform = CGAffineTransformIdentity;
    }];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    [self.transitionCoordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
        UIView *view = [context viewForKey:UITransitionContextToViewKey];
        view.transform = CGAffineTransformMakeScale(, );

    } completion:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
//        UIView *view = [context viewForKey:UITransitionContextToViewKey];
//        view.transform = CGAffineTransformIdentity;
    }];
}

- (void)dealloc
{
    self.interactiveAnimator = nil;
    self.dismissAnimator = nil;
}

- (void)btnClick:(UIButton *)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

#pragma mark - UIViewControllerTransitioningDelegate
//  return 动画对象，该动画对象符合 UIViewControllerAnimatedTransitioning 协议，负责显示 present 动画。
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
    return nil;
}
// return 动画对象，负责显示 dismiss 动画。
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    return self.dismissAnimator;
}
// return 交互式动画对象，该动画符合 UIViewControllerInteractiveTransitioning 协议，采用触摸手势或手势识别器作为动画的驱动，显示 present 动画。
- (id<UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id<UIViewControllerAnimatedTransitioning>)animator {
    return nil;
}
// return 交互式动画，显示 dismiss 动画
- (id<UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id<UIViewControllerAnimatedTransitioning>)animator {
    // 如果直接返回 interactive 会与系统的 dismiss 动画有冲突，导致点击 button 无法 dismiss 界面。
    // 同时如果返回  interactiveAnimator，那么 animationControllerForDismissedController: 则必须实现
    return self.interactiveAnimator.isInteractive? self.interactiveAnimator: nil;
//    return self.interactiveAnimator;
}

// return UIPresentationController，系统已经提供了各个演示样式。
//- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(UIViewController *)presenting sourceViewController:(UIViewController *)source NS_AVAILABLE_IOS(8_0);

@end

2. 实现一个动画对象, 实现 <UIViewControllerAnimatedTransitioning>协议

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {
    return 0.35f;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    UIViewController *srcVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIViewController *secondVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIView *containerView = [transitionContext containerView];

    [containerView addSubview:srcVC.view];

    [containerView addSubview:secondVC.view];

    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        secondVC.view.frame = CGRectMake(, [UIScreen mainScreen].bounds.size.height, secondVC.view.bounds.size.width, secondVC.view.bounds.size.height);
    } completion:^(BOOL finished) {
        [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
    }];
}

3. 交互式动画效果, 需要实现<UIViewControllerInteractiveTransitioning>协议 ; 或者继承UIPercentDrivenInteractiveTransition 类

* 可选实现. 在本例中, 通过pan手势下滑跟随dismiss, 需要通过交互式动画来实现

#import "CustomInteractiveTransition.h"
@interface CustomInteractiveTransition : UIPercentDrivenInteractiveTransition

@property (nonatomic, assign, readonly) BOOL isInteractive;

- (instancetype)initWithViewController:(UIViewController *)viewController;

- (void)panGestureAction:(UIPanGestureRecognizer *)gestureRecognizer;

@end
//.m
@interface CustomInteractiveTransition ()

@property (nonatomic, weak) UIViewController *viewController;

@property (nonatomic, assign) CGFloat startScale;

@property (nonatomic, assign, readwrite) BOOL isInteractive;

@end

@implementation CustomInteractiveTransition

- (instancetype)initWithViewController:(UIViewController *)viewController {
    if (self = [super init]) {
        _isInteractive = NO;
        _viewController = viewController;
    }
    return self;
}

- (void)panGestureAction:(UIPanGestureRecognizer *)recognizer {
    CGFloat progress = [recognizer translationInView:self.viewController.view].y / (self.viewController.view.bounds.size.height * 1.0);
    progress = MIN(1.0, MAX(0.0, progress));

    self.isInteractive = YES;

    if (recognizer.state == UIGestureRecognizerStateBegan) {

        [self.viewController dismissViewControllerAnimated:YES completion:^{

        }];
    }
    else if (recognizer.state == UIGestureRecognizerStateChanged) {
        [self updateInteractiveTransition:progress];
    }
    else if (recognizer.state == UIGestureRecognizerStateEnded || recognizer.state == UIGestureRecognizerStateCancelled) {
        if (progress > 0.5) {
            [self finishInteractiveTransition];
        }
        else {
            [self cancelInteractiveTransition];
        }

        self.isInteractive = NO;
    }
}

@end

在 iOS中，可以取消一个过渡。这意味着，第二个视图的 -viewWillApear 被调用，但 -viewDidApear不一定被调用。
如果代码写的假定 -viewDidAppear 总是在 -viewWillAppear 之后执行则需要重新考虑逻辑实现。
这种情况下UIViewControllerTransitionCoordinator 就有用了。在交互式过渡结束的时候，会在 block 中收到通知。

参考:

present:   https://www.jianshu.com/p/aed8a3a15c82

push/pop: https://www.jianshu.com/p/28b9523d70a9