原理

所谓转场动画无非就是从A跳转到B的过程中，通过拦截重写

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext

在其中我们可以获得三个视图：

fromView：转场开始视图（即A视图）
toView：转场结束视图（即B视图)
containerView：转场视图容器,所有转场动画在里面完成

这样一来，我们就能拿到AB视图里的所有元素和位置，把它放进containerView里，让A视图里的元素位移到B视图里对应的位置，完成转场，这样在视觉上就无缝衔接了

思路

有了理论基础我们再来谈思路，我们可以把这个动画先拆成两部分，即A到B，B到A两部分，然后A到B可以可以有点击Cell变小 --> 松手Cell回复正常 --> 转场，A的元素位移到B里对应的位置 --> A到B转场完成。 B到A差点多也是模糊背景 --> 缩小A视图 --> 转场，B的元素位移到A李对应的位置 --> B到A转场完成，其实都大同小异。

######让cell变小再正常一是为了给用户增加反馈，二是这样才符合运动规律，具体可以百度运动规律，要做好动画对物体的运动规律还是要有所了解，不然动画会十分生硬

实现

页面

先搭建出想要跳转的两个页面，这个比较简单，所以这里就不写了，重点还是放在动画上，不过要注意，做动画推荐用frame布局。

动画拆解根据上面拆解的动画步骤，一个个来实现

点击Cell变小

- (BOOL)tableView:(UITableView *)tableView shouldHighlightRowAtIndexPath:(NSIndexPath *)indexPath  {
	 _selectIndexPath = indexPath;
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    [UIView animateWithDuration:0.3 animations:^{
        cell.transform = CGAffineTransformMakeScale(0.8, 0.8);
    }];
    return YES;
}

松开回复正常

- (void)tableView:(UITableView *)tableView didUnhighlightRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    if ([_selectIndexPath isEqual:indexPath]) {
        [UIView animateWithDuration:0.3 animations:^{
            cell.transform = CGAffineTransformMakeScale(1, 1);
            return;
        }];
    }
}

转场，A的元素位移到B里对应的位置（重点）

我们先设置代理 self.navigationController.delegate = self; 实现代理

-(id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
    return self;
}
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext {
    return 1.0f;
}

当点击跳转时，会进入animateTransition:方法

// 修改转场动画
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    //获取的转场视图容器
    UIView *containerView = [transitionContext containerView];
    //获取的B控制器
    GSInfoViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    //获取b视图的背景图 这里需要注意，我是将b视图bg上lb的标签全部添加在bgImageView上，所以做动画时只拿到bgImageView就行了；
    UIView *toBgImageView = toVC.bgImageView;
    toBgImageView.hidden = YES;
    toVC.view.alpha = 0;
    //将B添加到转场视图容器里
    [containerView addSubview:toVC.view];
     
    //获取对应的A页面的cell
    GSTodayTableViewCell *cell = (GSTodayTableViewCell *)[self.tableView cellForRowAtIndexPath:[self.tableView indexPathForSelectedRow]];
    //获取A页面的各个元素
    //创建A页面的cell的背景，设置frame
    UIView *fromBgImageView = [[UIImageView alloc]initWithImage:cell.bgImageView.image];
    fromBgImageView.frame = [containerView convertRect:cell.bgImageView.frame fromView:cell.bgImageView.superview];
    //创建A页面的cell的标签，设置frame
    UILabel *typeL = [self copyLabel:cell.typeL];
    [fromBgImageView addSubview:typeL];
    //创建A页面的cell的标题，设置frame
    UILabel *contentLabel =[self copyLabel:cell.contentL];
    [fromBgImageView addSubview:contentLabel];
    //创建关闭按钮，虽然A页面没有该元素，但动画时会出现，这里的frame可以根据自己感觉调整
    UIButton *closeBtn = [UIButton buttonWithType:0];
    closeBtn.x = cell.width - 2*kMargin - 60;
    closeBtn.centerY = kHeight(20)-10;
    closeBtn.size = CGSizeMake(40, 40);
    closeBtn.alpha = 0.6;
    [closeBtn setBackgroundImage:[UIImage imageNamed:@"close"] forState:UIControlStateNormal];
    [fromBgImageView addSubview:closeBtn];
    //将A添加到转场视图容器里,注意，需要先添加B在添加A，应该A是在前面做动画的
    [containerView addSubview:fromBgImageView];
    
    //这里可以设置动画时间，弹性等
    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0.0f usingSpringWithDamping:0.6f initialSpringVelocity:1.0f options:UIViewAnimationOptionCurveLinear animations:^{
        [containerView layoutIfNeeded];
        toVC.view.alpha = 1.0f;
        //这里将B页面各个元素的frame给A页面对应的
        typeL.frame = toVC.typeL.frame ;
        closeBtn.frame = toVC.closeBtn.frame;
        contentLabel.frame = toVC.titleL.frame;
        fromBgImageView.frame = [containerView convertRect:toBgImageView.frame fromView:toBgImageView.superview];
    } completion:^(BOOL finished) {
        //都是为了动画弄出来的工具对象，全部删了隐藏了
        toBgImageView.hidden = NO;
        closeBtn.hidden = YES;
        [fromBgImageView removeFromSuperview];
        [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
    }];
}

上面用到的复制一个完整的label用方法

- (UILabel *)copyLabel:(UILabel *)label {
    UILabel *newLabel = [[UILabel alloc] init];
    newLabel.text = label.text;
    newLabel.font = label.font;
    newLabel.alpha = label.alpha;
    newLabel.frame =  label.frame;
    newLabel.textColor = label.textColor;
    newLabel.textAlignment = label.textAlignment;
    return newLabel;
}

这样从A跳转到B的过程场动画就完成了

接下做从B到A跳转的过程，其实差别并不大，一样的设置代理self.navigationController.delegate = self;，再加个背景毛玻璃

// 背景毛玻璃
UIBlurEffect *effect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleLight];
UIVisualEffectView *effectView = [[UIVisualEffectView alloc] initWithEffect:effect];
effectView.frame = CGRectMake(0, 0, kScreenW, kScreenH);
[self.view addSubview:effectView];

实现代理

-(id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
    return self;
}
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext {
    return 1.0f;
}

点击跳转进入animateTransition:

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    UIView *containerView = [transitionContext containerView];
    //获取跳转后的页面
    GSTodayViewController *toVC = (GSTodayViewController *)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    toVC.view.frame = [transitionContext finalFrameForViewController:toVC];
    //根据selectIndexPath获取对应的cell, selectIndexPath可以在跳转的时候传进来
    GSTodayTableViewCell *cell = (GSTodayTableViewCell *)[toVC.tableView cellForRowAtIndexPath:self.selectIndexPath];
    //获取cell的背景
    UIView *cellBgImageView = cell.bgImageView;
    cellBgImageView.hidden = YES;
    
    //获取当前页面
    GSInfoViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    //获取当前的背景图
    UIView *bgImageView = fromVC.bgImageView;
    bgImageView.hidden = YES;
    //创建背景图做动画用
    UIView *screenshotView = [bgImageView snapshotViewAfterScreenUpdates:NO];
    //圆角与cell保持一致
    screenshotView.layer.masksToBounds = YES;
    screenshotView.layer.cornerRadius = 15;
    screenshotView.frame = [containerView convertRect:bgImageView.frame fromView:bgImageView.superview];
    //创建标签
    UILabel *typeL = [self copyLabel:self.typeL];
    [screenshotView addSubview:typeL];
    //创建标题 到这里可以看出这个刚刚的一模一样
    UILabel *titleL =  [self copyLabel:self.titleL];
    [screenshotView addSubview:titleL];
    [containerView addSubview:screenshotView];
    [containerView insertSubview:toVC.view belowSubview:fromVC.view];
    //动画
    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:0.5f initialSpringVelocity:1.0 options:UIViewAnimationOptionCurveEaseIn animations:^{
        [containerView layoutIfNeeded];
        //隐藏当前视图
        fromVC.view.alpha = 0.0f;
        //转场过程中保持视图圆角
        screenshotView.layer.cornerRadius = 15;
        self.tableView.frame = CGRectMake(self.tableView.frame.origin.x, self.tableView.frame.origin.y, self.tableView.frame.size.width,kScreenW*1.3*0.8);
        self.tableView.layer.cornerRadius = 15;
        screenshotView.frame = [containerView convertRect:cellBgImageView.frame fromView:cellBgImageView.superview];
        //这里需要设置label的frame,与外层cell的位置保持一致就行，外层cell是里的元素frame是写死的，我这里也就一样写死
        typeL.x = kWidth(16);
        typeL.y = kHeight(20);
        titleL.x = kWidth(16);
        titleL.y = kHeight(20)+ typeL.height + 8;
        _closeBtn.alpha = 0;
    } completion:^(BOOL finished) {
        //一样，动画结束后该隐藏的隐藏，该删除的删除
        bgImageView.hidden = YES;
        [screenshotView removeFromSuperview];
        cellBgImageView.hidden = NO;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}

这样一个完整的A跳B，B返A的过场动画就搞定了。