抖音的转场动画—iOS

前言

今天带来的是抖音的转场动画实现废话不多说上图

这里需要用到前一篇文章的上下滑实现

如果对转场不是很了解的话可能学习会有一些难度和疑问.

转场调用代码

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    AwemeListViewController *awemeVC = [[AwemeListViewController alloc] init];
    awemeVC.transitioningDelegate = self; //0

    // 1
    UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:indexPath];
    // 2
    CGRect cellFrame = cell.frame;
    // 3
    CGRect cellConvertedFrame = [collectionView convertRect:cellFrame toView:collectionView.superview];

    //弹窗转场
    self.presentScaleAnimation.cellConvertFrame = cellConvertedFrame; //4

    //消失转场
    self.dismissScaleAnimation.selectCell = cell; // 5
    self.dismissScaleAnimation.originCellFrame  = cellFrame; //6
    self.dismissScaleAnimation.finalCellFrame = cellConvertedFrame; //7

    awemeVC.modalPresentationStyle = UIModalPresentationOverCurrentContext; //8
    self.modalPresentationStyle = UIModalPresentationCurrentContext; //9

    [self.leftDragInteractiveTransition wireToViewController:awemeVC];
    [self presentViewController:awemeVC animated:YES completion:nil];
}

0 处代码使我们需要把当前的类做为转场的代理
1 这里我们要拿出cell这个view
2 拿出当前Cell的frame坐标
3 cell的坐标转成屏幕坐标
4 设置弹出时候需要cell在屏幕的位置坐标
5 设置消失转场需要的选中cell视图
6 设置消失转场原始cell坐标位置
7 设置消失转场最终得cell屏幕坐标位置用于消失完成回到原来位置的动画
8 设置弹出得vc弹出样式这个用于显示弹出VC得时候默认底部使blua的高斯模糊
9 设置当前VC的模态弹出样式为当前的弹出上下文

5~7 步设置的消失转场动画下面会讲解

这里我们用的是前面讲上下滑的VC对象大家不必担心当它是一个普通的UIViewController即可

实现转场所需要的代理

首先在需要实现UIViewControllerTransitioningDelegate这个代理

 #pragma mark -
#pragma mark - UIViewControllerAnimatedTransitioning Delegate
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {

    return self.presentScaleAnimation; //present VC
}

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    return self.dismissScaleAnimation; //dismiss VC
}

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator {
    return self.leftDragInteractiveTransition.isInteracting? self.leftDragInteractiveTransition: nil;
}

这里面我们看到我们分别返回了

弹出动画实例self.presentScaleAnimation
dismiss动画实例self.dismissScaleAnimation
以及self.leftDragInteractiveTransition实例用于负责转场切换的具体实现

所以我们需要在当前的VC中声明3个成员变量并初始化

    @property (nonatomic, strong) PresentScaleAnimation *presentScaleAnimation;
    @property (nonatomic, strong) DismissScaleAnimation *dismissScaleAnimation;
    @property (nonatomic, strong) DragLeftInteractiveTransition *leftDragInteractiveTransition;

并在viewDidLoad:方法中初始化一下

 //转场的两个动画
self.presentScaleAnimation = [[PresentScaleAnimation alloc] init];
self.dismissScaleAnimation = [[DismissScaleAnimation alloc] init];
self.leftDragInteractiveTransition = [DragLeftInteractiveTransition new];

这里我说一下这三个成员都负责啥事

首先DragLeftInteractiveTransition类负责转场的手势过程,就是pan手势在这个类里面实现,并继承自UIPercentDrivenInteractiveTransition类,这是iOS7以后系统提供的转场基类必须在interactionControllerForDismissal:代理协议中返回这个类或者子类的实例对象,所以我们生成一个成员变量self.leftDragInteractiveTransition

其次是弹出present和消失dismiss的动画类,这俩类其实是负责简单的手势完成之后的动画.

这两个类都是继承自NSObject并实现UIViewControllerAnimatedTransitioning协议的类,这个协议里面有需要你复写某些方法返回具体的动画执行时间,和中间过程中我们需要的相关的容器视图以及控制器的视图实例,当我们自己执行完成之后调用相关的block回答告知转场是否完成就行了.

 @implementation PresentScaleAnimation
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext{
    return 0.3f;
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];    
    if (CGRectEqualToRect(self.cellConvertFrame, CGRectZero)) {
        [transitionContext completeTransition:YES];
        return;
    }
    CGRect initialFrame = self.cellConvertFrame;
    UIView *containerView = [transitionContext containerView];
    [containerView addSubview:toVC.view];
    CGRect finalFrame = [transitionContext finalFrameForViewController:toVC];
    NSTimeInterval duration = [self transitionDuration:transitionContext];
    toVC.view.center = CGPointMake(initialFrame.origin.x + initialFrame.size.width/2, initialFrame.origin.y + initialFrame.size.height/2);
    toVC.view.transform = CGAffineTransformMakeScale(initialFrame.size.width/finalFrame.size.width, initialFrame.size.height/finalFrame.size.height);
    [UIView animateWithDuration:duration
                          delay:0
         usingSpringWithDamping:0.8
          initialSpringVelocity:1
                       options:UIViewAnimationOptionLayoutSubviews
                     animations:^{
                         toVC.view.center = CGPointMake(finalFrame.origin.x + finalFrame.size.width/2, finalFrame.origin.y + finalFrame.size.height/2);
                         toVC.view.transform = CGAffineTransformMakeScale(1, 1);
                     } completion:^(BOOL finished) {
                         [transitionContext completeTransition:YES];
                     }];
}
@end

很简单.

消失的动画同上边差不多


@interface DismissScaleAnimation ()
@end
@implementation DismissScaleAnimation
- (instancetype)init {
    self = [super init];
    if (self) {
        _centerFrame = CGRectMake((ScreenWidth - 5)/2, (ScreenHeight - 5)/2, 5, 5);
    }
    return self;
}
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext{
    return 0.25f;
}
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
//    UINavigationController *toNavigation = (UINavigationController *)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
//    UIViewController *toVC = [toNavigation viewControllers].firstObject;

    UIView *snapshotView;
    CGFloat scaleRatio;
    CGRect finalFrame = self.finalCellFrame;
    if(self.selectCell && !CGRectEqualToRect(finalFrame, CGRectZero)) {
        snapshotView = [self.selectCell snapshotViewAfterScreenUpdates:NO];
        scaleRatio = fromVC.view.frame.size.width/self.selectCell.frame.size.width;
        snapshotView.layer.zPosition = 20;
    }else {
        snapshotView = [fromVC.view snapshotViewAfterScreenUpdates:NO];
        scaleRatio = fromVC.view.frame.size.width/ScreenWidth;
        finalFrame = _centerFrame;
    }

    UIView *containerView = [transitionContext containerView];
    [containerView addSubview:snapshotView];

    NSTimeInterval duration = [self transitionDuration:transitionContext];

    fromVC.view.alpha = 0.0f;
    snapshotView.center = fromVC.view.center;
    snapshotView.transform = CGAffineTransformMakeScale(scaleRatio, scaleRatio);
    [UIView animateWithDuration:duration
                          delay:0
         usingSpringWithDamping:0.8
          initialSpringVelocity:0.2
                       options:UIViewAnimationOptionCurveEaseInOut
                     animations:^{
                         snapshotView.transform = CGAffineTransformMakeScale(1.0f, 1.0f);
                         snapshotView.frame = finalFrame;
                     } completion:^(BOOL finished) {
                         [transitionContext finishInteractiveTransition];
                         [transitionContext completeTransition:YES];
                         [snapshotView removeFromSuperview];
                     }];
}
@end

我们重点需要说一下转场过渡的类DragLeftInteractiveTransition继承自UIPercentDrivenInteractiveTransition负责转场过程,

头文件的声明

@interface DragLeftInteractiveTransition : UIPercentDrivenInteractiveTransition
/** 是否正在拖动返回 标识是否正在使用转场的交互中 */
@property (nonatomic, assign) BOOL isInteracting;
/**
 设置需要返回的VC

 @param viewController 控制器实例
 */
-(void)wireToViewController:(UIViewController *)viewController;
@end

实现

@interface DragLeftInteractiveTransition ()
@property (nonatomic, strong) UIViewController *presentingVC;
@property (nonatomic, assign) CGPoint viewControllerCenter;
@property (nonatomic, strong) CALayer *transitionMaskLayer;
@end
@implementation DragLeftInteractiveTransition
#pragma mark -
#pragma mark - override methods 复写方法
-(CGFloat)completionSpeed{
    return 1 - self.percentComplete;
}
- (void)updateInteractiveTransition:(CGFloat)percentComplete {
    NSLog(@"%.2f",percentComplete);

}
- (void)cancelInteractiveTransition {
    NSLog(@"转场取消");
}
- (void)finishInteractiveTransition {
    NSLog(@"转场完成");
}
- (CALayer *)transitionMaskLayer {
    if (_transitionMaskLayer == nil) {
        _transitionMaskLayer = [CALayer layer];
    }
    return _transitionMaskLayer;
}
#pragma mark -
#pragma mark - private methods 私有方法
- (void)prepareGestureRecognizerInView:(UIView*)view {
    UIPanGestureRecognizer *gesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)];
    [view addGestureRecognizer:gesture];
}
#pragma mark -
#pragma mark - event response 所有触发的事件响应 按钮、通知、分段控件等
- (void)handleGesture:(UIPanGestureRecognizer *)gestureRecognizer {
    UIView *vcView = gestureRecognizer.view;
    CGPoint translation = [gestureRecognizer translationInView:vcView.superview];
    if(!self.isInteracting &&
       (translation.x < 0 ||
        translation.y < 0 ||
        translation.x < translation.y)) {
        return;
    }
    switch (gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:{
            //修复当从右侧向左滑动的时候的bug 避免开始的时候从又向左滑动 当未开始的时候
            CGPoint vel = [gestureRecognizer velocityInView:gestureRecognizer.view];
            if (!self.isInteracting && vel.x < 0) {
                self.isInteracting = NO;
                return;
            }
            self.transitionMaskLayer.frame = vcView.frame;
            self.transitionMaskLayer.opaque = NO;
            self.transitionMaskLayer.opacity = 1;
            self.transitionMaskLayer.backgroundColor = [UIColor whiteColor].CGColor; //必须有颜色不能透明
            [self.transitionMaskLayer setNeedsDisplay];
            [self.transitionMaskLayer displayIfNeeded];
            self.transitionMaskLayer.anchorPoint = CGPointMake(0.5, 0.5);
            self.transitionMaskLayer.position = CGPointMake(vcView.frame.size.width/2.0f, vcView.frame.size.height/2.0f);
            vcView.layer.mask = self.transitionMaskLayer;
            vcView.layer.masksToBounds = YES;

            self.isInteracting = YES;
        }

            break;
        case UIGestureRecognizerStateChanged: {
            CGFloat progress = translation.x / [UIScreen mainScreen].bounds.size.width;
            progress = fminf(fmaxf(progress, 0.0), 1.0);

            CGFloat ratio = 1.0f - progress*0.5f;
            [_presentingVC.view setCenter:CGPointMake(_viewControllerCenter.x + translation.x * ratio, _viewControllerCenter.y + translation.y * ratio)];
            _presentingVC.view.transform = CGAffineTransformMakeScale(ratio, ratio);
            [self updateInteractiveTransition:progress];
            break;
        }
        case UIGestureRecognizerStateCancelled:
        case UIGestureRecognizerStateEnded:{
            CGFloat progress = translation.x / [UIScreen mainScreen].bounds.size.width;
            progress = fminf(fmaxf(progress, 0.0), 1.0);
            if (progress < 0.2){
                [UIView animateWithDuration:progress
                                      delay:0
                          options:UIViewAnimationOptionCurveEaseOut
                                 animations:^{
                                     CGFloat w = [UIScreen mainScreen].bounds.size.width;
                                     CGFloat h = [UIScreen mainScreen].bounds.size.height;
                                     [self.presentingVC.view setCenter:CGPointMake(w/2, h/2)];
                                     self.presentingVC.view.transform = CGAffineTransformMakeScale(1.0f, 1.0f);
                                 } completion:^(BOOL finished) {
                                     self.isInteracting = NO;
                                     [self cancelInteractiveTransition];
                                 }];
            }else {
                _isInteracting = NO;
                [self finishInteractiveTransition];
                [_presentingVC dismissViewControllerAnimated:YES completion:nil];
            }
            //移除 遮罩
            [self.transitionMaskLayer removeFromSuperlayer];
            self.transitionMaskLayer = nil;
        }
            break;
        default:
            break;
    }
}
#pragma mark -
#pragma mark - public methods 公有方法
-(void)wireToViewController:(UIViewController *)viewController {
    self.presentingVC = viewController;
    self.viewControllerCenter = viewController.view.center;
    [self prepareGestureRecognizerInView:viewController.view];
}
@end

我们对外提供了一个wireToViewController:方法用于外部需要创建转场使用.

前面的代码我们发现有一处

[self.leftDragInteractiveTransition wireToViewController:awemeVC];
[self presentViewController:awemeVC animated:YES completion:nil];

这里就是需要把我们要弹出的上下滑VC实例传进来,进来之后为VC的self.view加个pan手势,

复写方法中我们可以看到相关开始结束完成过程的百分比相关方法复写

#pragma mark -
#pragma mark - override methods 复写方法
-(CGFloat)completionSpeed{
    return 1 - self.percentComplete;
}
- (void)updateInteractiveTransition:(CGFloat)percentComplete {
    NSLog(@"%.2f",percentComplete);
}
- (void)cancelInteractiveTransition {
    NSLog(@"转场取消");
}
- (void)finishInteractiveTransition {
    NSLog(@"转场完成");
}

看是手势出发前先检查一下是否如下条件

UIView *vcView = gestureRecognizer.view;
CGPoint translation = [gestureRecognizer translationInView:vcView.superview];
if(!self.isInteracting &&
   (translation.x < 0 ||
    translation.y < 0 ||
    translation.x < translation.y)) {
    return;
}

拿出手势作用的视图,然后坐标转换,判断当前是否已经开始了动画,如果没开始或者x坐标 < y坐标是判断当前是否是超过边界范围等等异常case处理.

开始的时候需要注意下

//修复当从右侧向左滑动的时候的bug 避免开始的时候从又向左滑动 当未开始的时候
CGPoint vel = [gestureRecognizer velocityInView:gestureRecognizer.view];
if (!self.isInteracting && vel.x < 0) {
    self.isInteracting = NO;
    return;
}

然后开始的时候加个蒙版做为view.mask 这样是为了解决tableView 超出contentSize的范围要隐藏

剩下的就是中间过程

关键的核心代码

[self updateInteractiveTransition:progress];

更新转场的进度这是这个类的自带方法,调用就行了

最后手势结束

CGFloat progress = translation.x / [UIScreen mainScreen].bounds.size.width;
progress = fminf(fmaxf(progress, 0.0), 1.0);
if (progress < 0.2){
    [UIView animateWithDuration:progress
                          delay:0
                        options:UIViewAnimationOptionCurveEaseOut
                     animations:^{
                         CGFloat w = [UIScreen mainScreen].bounds.size.width;
                         CGFloat h = [UIScreen mainScreen].bounds.size.height;
                         [self.presentingVC.view setCenter:CGPointMake(w/2, h/2)];
                         self.presentingVC.view.transform = CGAffineTransformMakeScale(1.0f, 1.0f);
                     } completion:^(BOOL finished) {
                         self.isInteracting = NO;
                         [self cancelInteractiveTransition];
                     }];
}else {
    _isInteracting = NO;
    [self finishInteractiveTransition];
    [_presentingVC dismissViewControllerAnimated:YES completion:nil];
}
//移除 遮罩
[self.transitionMaskLayer removeFromSuperlayer];
self.transitionMaskLayer = nil;

这里设置0.2的容差如果你觉得这个应该开放接口设置可自行封装.

当用户取消的话记得调用cancelInteractiveTransition方法取消

完成的话调用finishInteractiveTransition完成转场

总结

整个过程还是比较简单的如果看过喵神的文章将会更加清晰的了解转场的三个过程
就是弹出和消失动画以及一个中间转场过程需要我们熟悉.

优化点: 在原开源工程中的demo转场右滑是有bug的,我做了一下如下判断

//修复当从右侧向左滑动的时候的bug 避免开始的时候从又向左滑动 当未开始的时候
CGPoint vel = [gestureRecognizer velocityInView:gestureRecognizer.view];
if (!self.isInteracting && vel.x < 0) {
    self.isInteracting = NO;
    return;
}

vel这个变量其实是判断当我们从右侧划入返回.修复了原来开源的一个bug

还有原来开源中tableView的contentSize以外区域露在外部,我用了一个mask的蒙版遮住了显示在外的区域.

唯一有些许遗憾的地方是抖音的左滑返回时候,有背景遮盖透明的渐变.

如果需要抖音的转场动画Demo，可以加iOS高级技术交流群：937194184，获取Demo,以及更多iOS学习资料

转载：原文地址

最后编辑于：2020.03.30 15:20:41

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抖音的转场动画—iOS

前言

转场调用代码

实现转场所需要的代理

总结

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