瀏覽大圖的一種實現方式

利用轉場動畫實現（這裡不說轉場動畫），主要就是幾個坐標的轉換：將cell上的imageView快照生成一個snapView（直接創建一個ImageVIew也一樣）， 在將cell上image的frame 坐標轉換到containerView上，在將snapView放大到目標尺寸 （首先你要知道轉場動畫時怎麼一回事）。

下麵是主要代碼，一個自定義類繼承自NSObject。實現了UINavigationControllerDelegate、UIViewControllerAnimatedTransitioning協議

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    
    // 獲取當前的控制器
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    
    // 獲取將要轉向的控制器
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    // 獲取容器視圖
    UIView *containerView = [transitionContext containerView];
    
    UICollectionView *collectionView ;
    UIImageView *contentImageView;
    if (self.opration == PushAnimationOprationPush) {
        
        ViewController *from =  (ViewController *)fromVC;
        collectionView = from.collectionView;
        
        contentImageView = [toVC valueForKey:@"_contentImageView"];
    }else {
        
        ViewController *to =  (ViewController *)toVC;
        collectionView = to.collectionView;
        contentImageView = [fromVC valueForKey:@"_contentImageView"];
    }
    
    // 獲取選中的cell 的indexpath
    NSArray *selectedItems = [collectionView indexPathsForSelectedItems];
    
    // 根據indexpath 獲取 cell
    CusCollectionViewCell *cell = (CusCollectionViewCell *)[collectionView cellForItemAtIndexPath:[selectedItems firstObject]];
    
    UIView *snapView;
    CGRect snapViewFrame;
    CGRect snapViewTargetFrame;
    
    if (self.opration == PushAnimationOprationPush) {
        
        // 截取cell 上contentImage 的快照
        snapView = [cell.contentImage snapshotViewAfterScreenUpdates:NO];
        
        // 根據contentImage在cell上的坐標 轉換到 containerView上
        snapViewFrame = [containerView convertRect:cell.contentImage.frame fromView:cell.contentImage.superview];
        
        // 獲取目標控制器上要顯示的 imageView，並根據該imageView的尺寸位置，轉換到 容器視圖上，成為snapView 最終尺寸。
        snapViewTargetFrame = [containerView convertRect:contentImageView.frame fromView:contentImageView.superview];

    }else {
        
        snapView = [contentImageView snapshotViewAfterScreenUpdates:NO];
        
        snapViewFrame = [containerView convertRect:contentImageView.frame fromView:contentImageView.superview];
        
        snapViewTargetFrame = [containerView convertRect:cell.contentImage.frame fromView:cell.contentImage];
        
    }
    
    snapView.frame = snapViewFrame;
    toVC.view.alpha = 0;
    
    [containerView addSubview:toVC.view];
    [containerView addSubview:snapView];
    
    contentImageView.hidden = YES;
    cell.contentImage.hidden = YES;
    
    
    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:0.6f initialSpringVelocity:1.0f options:UIViewAnimationOptionCurveEaseInOut animations:^{
        snapView.frame = snapViewTargetFrame;
        toVC.view.alpha = 1.0;
    } completion:^(BOOL finished) {
        
        contentImageView.hidden = NO;
        cell.contentImage.hidden = NO;
        [snapView removeFromSuperview];
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
    
}

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
    
    if (operation == UINavigationControllerOperationPush) {
        
        self.opration = PushAnimationOprationPush;
        
    }else if (operation == UINavigationControllerOperationPop) {
        
        self.opration = PushAnimationOprationPop;
    }
    return self;
}

- (void)start {
    self.nav.delegate = self;
}

/** 為目標控制器添加一個tap手勢，返回上一個控制器 */
- (void)tapGestureToPopWithController:(UIViewController *)targetVC {
    
    self.targetViewController = targetVC;
    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapGesture:)];
    [targetVC.view addGestureRecognizer:tapGesture];
}

- (void)tapGesture:(UITapGestureRecognizer *)gesture {
    
    [self.targetViewController.navigationController popViewControllerAnimated:YES];
}