UITabBarControllerDelegate delegate
- (id <UIViewControllerInteractiveTransitioning>)tabBarController:(UITabBarController *)tabBarController
interactionControllerForAnimationController: (id <UIViewControllerAnimatedTransitioning>)animationController NS_AVAILABLE_IOS(7_0);
- (id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
animationControllerForTransitionFromViewController:(UIViewController *)fromVC
toViewController:(UIViewController *)toVC NS_AVAILABLE_IOS(7_0);

/**
 *  自定義的動畫類
 *  實現(xiàn)協(xié)議------>@protocol UIViewControllerAnimatedTransitioning
 *  這個接口負責切換的具體內(nèi)容，也即“切換中應該發(fā)生什么”
 */ 
@interface MTHCustomAnimator : NSObject <UIViewControllerAnimatedTransitioning> 
 
@end 
 
@implementation MTHCustomAnimator 
 
// 系統(tǒng)給出一個切換上下文，我們根據(jù)上下文環(huán)境返回這個切換所需要的花費時間 
- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext 
{ 
    return 1.0; 
} 
 
// 完成容器轉場動畫的主要方法，我們對于切換時的UIView的設置和動畫都在這個方法中完成 
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext 
{ 
    // 可以看做為destination ViewController 
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey]; 
    // 可以看做為source ViewController 
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey]; 
    // 添加toView到容器上 
        // 如果是XCode6 就可以用這段 
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0) 
    { 
        // iOS8 SDK 新API 
        UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey]; 
        //UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey]; 
        [[transitionContext containerView] addSubview:toView]; 
    }else{ 
        // 添加toView到容器上 
        [[transitionContext containerView] addSubview:toViewController.view]; 
    } 
     
    // 如果是XCode5 就是用這段 
    [[transitionContext containerView] addSubview:toViewController.view]; 
    toViewController.view.alpha = 0.0; 
    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{ 
        // 動畫效果有很多,這里就展示個左偏移 
        fromViewController.view.transform = CGAffineTransformMakeTranslation(-320, 0); 
        toViewController.view.alpha = 1.0; 
    } completion:^(BOOL finished) { 
        fromViewController.view.transform = CGAffineTransformIdentity; 
        // 聲明過渡結束-->記住，一定別忘了在過渡結束時調(diào)用 completeTransition: 這個方法 
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]]; 
    }]; 
} 

     
// MainViewController 
@interface MTHMainViewController () <UINavigationControllerDelegate,UIViewControllerTransitioningDelegate> 
 
@property (nonatomic,strong) MTHCustomAnimator *customAnimator; 
@property (nonatomic,strong) PDTransitionAnimator *minToMaxAnimator; 
@property (nonatomic,strong) MTHNextViewController *nextVC; 
// 交互控制器 (Interaction Controllers) 通過遵從 UIViewControllerInteractiveTransitioning 協(xié)議來控制可交互式的轉場。 
@property (strong, nonatomic) UIPercentDrivenInteractiveTransition* interactionController; 
@end 
 
@implementation MTHMainViewController 
 
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil 
{ 
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; 
    if (self) { 
        // Custom initialization 
    } 
    return self; 
} 
 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    // Do any additional setup after loading the view. 
    self.navigationItem.title = @"Demo"; 
    self.view.backgroundColor = [UIColor yellowColor]; 
    // 設置代理 
    self.navigationController.delegate = self; 
    // 設置轉場動畫 
    self.customAnimator = [[MTHCustomAnimator alloc] init]; 
    self.minToMaxAnimator = [PDTransitionAnimator new]; 
 
    self.nextVC = [[MTHNextViewController alloc] init]; 
    // Present的代理和自定義設置 
    _nextVC.transitioningDelegate = self; 
    _nextVC.modalPresentationStyle = UIModalPresentationCustom; (貌似有BUG)換成modalTransitionStyle = UIModalPresentationCustom 
     
    // Push 
    UIButton *pushButton = [UIButton buttonWithType:UIButtonTypeSystem]; 
    pushButton.frame = CGRectMake(140, 200, 40, 40); 
    [pushButton setTitle:@"Push" forState:UIControlStateNormal]; 
    [pushButton addTarget:self action:@selector(push) forControlEvents:UIControlEventTouchUpInside]; 
    [self.view addSubview:pushButton]; 
     
    // Present 
    UIButton *modalButton = [UIButton buttonWithType:UIButtonTypeSystem]; 
    modalButton.frame = CGRectMake(265, 500, 50, 50); 
    [modalButton setTitle:@"Modal" forState:UIControlStateNormal]; 
    [modalButton addTarget:self action:@selector(modal) forControlEvents:UIControlEventTouchUpInside]; 
    [self.view addSubview:modalButton]; 
     
    // 實現(xiàn)交互操作的手勢 
    UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(didClickPanGestureRecognizer:)]; 
    [self.navigationController.view addGestureRecognizer:panRecognizer]; 
} 
 
 
- (void)push 
{ 
    [self.navigationController pushViewController:_nextVC animated:YES]; 
} 
 
- (void)modal 
{ 
    [self presentViewController:_nextVC animated:YES completion:nil]; 
} 
 
#pragma mark - UINavigationControllerDelegate iOS7新增的2個方法 
// 動畫特效 
- (id<UIViewControllerAnimatedTransitioning>) navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC 
{ 
    /**
     *  typedef NS_ENUM(NSInteger, UINavigationControllerOperation) {
     *     UINavigationControllerOperationNone,
     *     UINavigationControllerOperationPush,
     *     UINavigationControllerOperationPop,
     *  };
     */ 
    if (operation == UINavigationControllerOperationPush) { 
        return self.customAnimator; 
    }else{ 
        return nil; 
    } 
} 
 
// 交互 
- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController*)navigationController                           interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>)animationController 
{ 
    /**
     *  在非交互式動畫效果中，該方法返回 nil
     *  交互式轉場,自我理解意思是,用戶能通過自己的動作來(常見:手勢)控制,不同于系統(tǒng)缺省給定的push或者pop(非交互式)
     */ 
    return _interactionController; 
}  
 
#pragma mark - Transitioning Delegate (Modal) 
// 前2個用于動畫 
-(id<UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source 
{ 
    self.minToMaxAnimator.animationType = AnimationTypePresent; 
    return _minToMaxAnimator; 
} 
 
-(id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed 
{ 
    self.minToMaxAnimator.animationType = AnimationTypeDismiss; 
    return _minToMaxAnimator; 
} 
 
// 后2個用于交互 
- (id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator 
{ 
    return _interactionController; 
} 
 
- (id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator 
{ 
    return nil; 
} 

#pragma mark - 手勢交互的主要實現(xiàn)--->UIPercentDrivenInteractiveTransition 
- (void)didClickPanGestureRecognizer:(UIPanGestureRecognizer*)recognizer 
{ 
    UIView* view = self.view; 
    if (recognizer.state == UIGestureRecognizerStateBegan) { 
        // 獲取手勢的觸摸點坐標 
        CGPoint location = [recognizer locationInView:view]; 
        // 判斷,用戶從右半邊滑動的時候,推出下一個VC(根據(jù)實際需要是推進還是推出) 
        if (location.x > CGRectGetMidX(view.bounds) && self.navigationController.viewControllers.count == 1){ 
            self.interactionController = [[UIPercentDrivenInteractiveTransition alloc] init]; 
            // 
            [self presentViewController:_nextVC animated:YES completion:nil]; 
        } 
    } else if (recognizer.state == UIGestureRecognizerStateChanged) { 
        // 獲取手勢在視圖上偏移的坐標 
        CGPoint translation = [recognizer translationInView:view]; 
        // 根據(jù)手指拖動的距離計算一個百分比，切換的動畫效果也隨著這個百分比來走 
        CGFloat distance = fabs(translation.x / CGRectGetWidth(view.bounds)); 
        // 交互控制器控制動畫的進度 
        [self.interactionController updateInteractiveTransition:distance]; 
    } else if (recognizer.state == UIGestureRecognizerStateEnded) { 
        CGPoint translation = [recognizer translationInView:view]; 
        // 根據(jù)手指拖動的距離計算一個百分比，切換的動畫效果也隨著這個百分比來走 
        CGFloat distance = fabs(translation.x / CGRectGetWidth(view.bounds)); 
        // 移動超過一半就強制完成 
        if (distance > 0.5) { 
            [self.interactionController finishInteractiveTransition]; 
        } else { 
            [self.interactionController cancelInteractiveTransition]; 
        } 
        // 結束后一定要置為nil 
        self.interactionController = nil; 
    } 
} 

@implementation PDTransitionAnimator 
 
#define Switch_Time 1.2 
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext { 
    return Switch_Time; 
} 
 
#define Button_Width 50.f 
#define Button_Space 10.f 
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext { 
    UIViewController* toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey]; 
    UIViewController* fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey]; 
 
    UIView * toView = toViewController.view; 
    UIView * fromView = fromViewController.view; 
     
    if (self.animationType == AnimationTypeDismiss) { 
        // 這個方法能夠高效的將當前顯示的view截取成一個新的view.你可以用這個截取的view用來顯示.例如,也許你只想用一張截圖來做動畫,畢竟用原始的view做動畫代價太高.因為是截取了已經(jīng)存在的內(nèi)容,這個方法只能反應出這個被截取的view當前的狀態(tài)信息,而不能反應這個被截取的view以后要顯示的信息.然而,不管怎么樣,調(diào)用這個方法都會比將view做成截圖來加載效率更高. 
        UIView * snap = [toView snapshotViewAfterScreenUpdates:YES]; 
        [transitionContext.containerView addSubview:snap]; 
        [snap setFrame:CGRectMake([UIScreen mainScreen].bounds.size.width - Button_Width - Button_Space, [UIScreen mainScreen].bounds.size.height - Button_Width - Button_Space, Button_Width, Button_Width)]; 
         
        [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{ 
            [snap setFrame:[UIScreen mainScreen].bounds]; 
        } completion:^(BOOL finished) { 
            [UIView animateWithDuration:0.5 animations:^{ 
                [[transitionContext containerView] addSubview:toView]; 
                snap.alpha = 0;  
            } completion:^(BOOL finished) { 
                [snap removeFromSuperview]; 
                [transitionContext completeTransition:![transitionContext transitionWasCancelled]]; 
            }]; 
        }]; 
    } else { 
        UIView * snap2 = [toView snapshotViewAfterScreenUpdates:YES]; 
        [transitionContext.containerView addSubview:snap2]; 
        UIView * snap = [fromView snapshotViewAfterScreenUpdates:YES]; 
        [transitionContext.containerView addSubview:snap]; 
         
        [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{ 
            [snap setFrame:CGRectMake([UIScreen mainScreen].bounds.size.width - Button_Width - Button_Space+ (Button_Width/2), [UIScreen mainScreen].bounds.size.height - Button_Width - Button_Space + (Button_Width/2), 0, 0)]; 
        } completion:^(BOOL finished) { 
            [UIView animateWithDuration:0.5 animations:^{ 
                //snap.alpha = 0; 
            } completion:^(BOOL finished) { 
                [snap removeFromSuperview]; 
                [snap2 removeFromSuperview]; 
                [[transitionContext containerView] addSubview:toView]; 
                // 切記不要忘記了噢 
                [transitionContext completeTransition:![transitionContext transitionWasCancelled]]; 
            }]; 
        }]; 
         
    } 
} 

[view snapshotViewAfterScreenUpdates:NO];

[view snapshotViewAfterScreenUpdates:YES];
[view setAlpha:0.0];

// ContainerViewController 
@interface FTContainerViewController ()  
 
@property (strong, nonatomic) FTPhotoSenderViewController       *photoSenderViewController; 
@property (strong, nonatomic) FTVideoSenderViewController       *videoSenderViewController; 
@property (strong, nonatomic) FTFileSenderViewController        *fileSenderViewController; 
@property (strong, nonatomic) FTContactSenderViewController     *contactSenderViewController; 
@property (strong, nonatomic) FTClipboardSenderViewController   *clipboardSenderViewController; 
@property (strong, nonatomic) UIViewController                  *selectedViewController;        // 當前選擇的VC 
@property (strong, nonatomic) NSArray                           *viewControllers;               // childVC數(shù)組 
@property (assign, nonatomic) NSInteger                         currentControllerIndex;         // 當前選擇的VC的數(shù)組下標號 
 
 
@end 
 
@implementation FTContainerViewController 
 
#pragma mark - ViewLifecycle Methods 
 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    // childVC 
    self.photoSenderViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FTPhotoSenderViewController"]; 
    self.videoSenderViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FTVideoSenderViewController"]; 
    self.fileSenderViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FTFileSenderViewController"]; 
    self.contactSenderViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FTContactSenderViewController"]; 
    self.clipboardSenderViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FTClipboardSenderViewController"]; 
    // 存儲childVC的數(shù)組 
    self.viewControllers = @[_photoSenderViewController,_videoSenderViewController,_fileSenderViewController,_contactSenderViewController,_clipboardSenderViewController]; 
    // 缺省為下標為0的VC 
    self.selectedViewController = self.selectedViewController ?: self.viewControllers[0]; 
    self.currentControllerIndex = 0; 
} 

#import "FTMthTransitionAnimator.h" 
 
@implementation FTMthTransitionAnimator 
 
static CGFloat const kChildViewPadding = 16; 
static CGFloat const kDamping = 0.5;    // damping參數(shù)代表彈性阻尼，隨著阻尼值越來越接近0.0，動畫的彈性效果會越來越明顯，而如果設置阻尼值為1.0，則視圖動畫不會有彈性效果 
static CGFloat const kInitialSpringVelocity = 0.5;  // 初始化彈簧速率 
 
- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext 
{ 
    return 1.0; 
} 
 
- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext 
{ 
    /**
     *  - viewControllerForKey：我們可以通過他訪問過渡的兩個 ViewController。
     *  - containerView：兩個 ViewController 的 containerView。
     *  - initialFrameForViewController 和 finalFrameForViewController 是過渡開始和結束時每個 ViewController 的 frame。
     */ 
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey]; 
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey]; 
     
    [[transitionContext containerView] addSubview:toViewController.view]; 
    toViewController.view.alpha = 0; 
    BOOL goingRight = ([transitionContext initialFrameForViewController:toViewController].origin.x < [transitionContext finalFrameForViewController:toViewController].origin.x); 
    CGFloat transDistance = [transitionContext containerView].bounds.size.width + kChildViewPadding; 
    CGAffineTransform transform = CGAffineTransformMakeTranslation(goingRight ? transDistance : -transDistance, 0); 
    // CGAffineTransformInvert 反轉 
    toViewController.view.transform = CGAffineTransformInvert(transform); 
//    toViewController.view.transform = CGAffineTransformTranslate(toViewController.view.transform, (goingRight ? transDistance : -transDistance), 0); 
     
    /**
     *   ----------彈簧動畫.....-------
     *  使用由彈簧的運動描述的時序曲線` animations` 。當` dampingRatio`為1時，動畫將平穩(wěn)減速到其最終的模型值不會振蕩。阻尼比小于1來完全停止前將振蕩越來越多?？梢允褂脧椈傻某跏妓俣龋灾付ǖ乃俣仍谀M彈簧的端部的物體被移動它附著之前。這是一個單元坐標系，其中1是指行駛總距離的動畫在第二。所以，如果你改變一個物體的位置由200PT在這個動畫，以及你想要的動畫表現(xiàn)得好像物體在動，在100PT /秒的動畫開始之前，你會通過0.5 。你通常會想通過0的速度。
     */ 
    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:kDamping initialSpringVelocity:kInitialSpringVelocity options:0x00 animations:^{ 
        fromViewController.view.transform = transform; 
        fromViewController.view.alpha = 0; 
        // CGAffineTransformIdentity  重置,初始化 
        toViewController.view.transform = CGAffineTransformIdentity; 
        toViewController.view.alpha = 1; 
    } completion:^(BOOL finished) { 
        fromViewController.view.transform = CGAffineTransformIdentity; 
        // 聲明過渡結束-->記住，一定別忘了在過渡結束時調(diào)用 completeTransition: 這個方法。 
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]]; 
    }]; 
} 
 
@end 

@interface FTMthTransitionContext : NSObject <UIViewControllerContextTransitioning> 
 
- (instancetype)initWithFromViewController:(UIViewController *)fromViewController toViewController:(UIViewController *)toViewController goingRight:(BOOL)goingRight; 
@property (nonatomic, copy) void (^completionBlock)(BOOL didComplete); 
@property (nonatomic, assign, getter=isAnimated) BOOL animated; 
@property (nonatomic, assign, getter=isInteractive) BOOL interactive; // 是否交互式 
 
@property (nonatomic, strong) NSDictionary *privateViewControllers; 
@property (nonatomic, assign) CGRect privateDisappearingFromRect; 
@property (nonatomic, assign) CGRect privateAppearingFromRect; 
@property (nonatomic, assign) CGRect privateDisappearingToRect; 
@property (nonatomic, assign) CGRect privateAppearingToRect; 
@property (nonatomic, weak) UIView *containerView; 
@property (nonatomic, assign) UIModalPresentationStyle presentationStyle; 
 
@end 
 
@implementation FTMthTransitionContext 
 
- (instancetype)initWithFromViewController:(UIViewController *)fromViewController toViewController:(UIViewController *)toViewController goingRight:(BOOL)goingRight { 
     
    if ((self = [super init])) { 
        self.presentationStyle = UIModalPresentationCustom; 
        self.containerView = fromViewController.view.superview; 
        self.privateViewControllers = @{ 
                                        UITransitionContextFromViewControllerKey:fromViewController, 
                                        UITransitionContextToViewControllerKey:toViewController, 
                                        }; 
         
        // Set the view frame properties which make sense in our specialized ContainerViewController context. Views appear from and disappear to the sides, corresponding to where the icon buttons are positioned. So tapping a button to the right of the currently selected, makes the view disappear to the left and the new view appear from the right. The animator object can choose to use this to determine whether the transition should be going left to right, or right to left, for example. 
        CGFloat travelDistance = (goingRight ? -self.containerView.bounds.size.width : self.containerView.bounds.size.width); 
        self.privateDisappearingFromRect = self.privateAppearingToRect = self.containerView.bounds; 
        self.privateDisappearingToRect = CGRectOffset (self.containerView.bounds, travelDistance, 0); 
        self.privateAppearingFromRect = CGRectOffset (self.containerView.bounds, -travelDistance, 0); 
    } 
     
    return self; 
} 
 
- (CGRect)initialFrameForViewController:(UIViewController *)viewController { 
    if (viewController == [self viewControllerForKey:UITransitionContextFromViewControllerKey]) { 
        return self.privateDisappearingFromRect; 
    } else { 
        return self.privateAppearingFromRect; 
    } 
} 
 
- (CGRect)finalFrameForViewController:(UIViewController *)viewController { 
    if (viewController == [self viewControllerForKey:UITransitionContextFromViewControllerKey]) { 
        return self.privateDisappearingToRect; 
    } else { 
        return self.privateAppearingToRect; 
    } 
} 
 
- (UIViewController *)viewControllerForKey:(NSString *)key { 
    return self.privateViewControllers[key]; 
} 
 
- (void)completeTransition:(BOOL)didComplete { 
    if (self.completionBlock) { 
        self.completionBlock (didComplete); 
    } 
} 
 
// 非交互式,直接返回NO,因為不允許交互當然也就無法操作進度取消 
- (BOOL)transitionWasCancelled { return NO; } 
 
// 非交互式,直接不進行操作,只有進行交互,下面3個協(xié)議方法才有意義,可參照系統(tǒng)給我們定義好的交互控制器 
// @interface UIPercentDrivenInteractiveTransition : NSObject <UIViewControllerInteractiveTransitioning> 
- (void)updateInteractiveTransition:(CGFloat)percentComplete {} 
- (void)finishInteractiveTransition {} 
- (void)cancelInteractiveTransition {} 
 
@end 

UISwipeGestureRecognizer *leftGesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swapController:)]; 
[leftGesture setDirection:UISwipeGestureRecognizerDirectionLeft]; 
[self.view addGestureRecognizer:leftGesture]; 
 
UISwipeGestureRecognizer *rightGesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swapController:)]; 
[rightGesture setDirection:UISwipeGestureRecognizerDirectionRight]; 
[self.view addGestureRecognizer:rightGesture]; 
[objc] view plaincopy
// 響應手勢的方法 
- (void)swapViewControllers:(UISwipeGestureRecognizer *)swipeGestureRecognizer 
{ 
    if (swipeGestureRecognizer.direction == UISwipeGestureRecognizerDirectionLeft) { 
        if (_currentControllerIndex < 4) { 
            _currentControllerIndex++; 
        } 
        NSLog(@"_currentControllerIndex = %ld",(long)_currentControllerIndex); 
        UIViewController *selectedViewController = self.viewControllers[_currentControllerIndex]; 
         NSLog(@"%s__%d__|%@",__FUNCTION__,__LINE__,@"右邊"); 
         self.selectedViewController = selectedViewController; 
    } else if (swipeGestureRecognizer.direction == UISwipeGestureRecognizerDirectionRight){ 
         NSLog(@"%s__%d__|%@",__FUNCTION__,__LINE__,@"左邊"); 
        if (_currentControllerIndex > 0) { 
            _currentControllerIndex--; 
        } 
        UIViewController *selectedViewController = self.viewControllers[_currentControllerIndex]; 
        self.selectedViewController = selectedViewController; 
    } 
} 
 
// 重寫selectedViewController的setter 
- (void)setSelectedViewController:(UIViewController *)selectedViewController 
{ 
    NSParameterAssert (selectedViewController); 
    [self _transitionToChildViewController:selectedViewController]; 
    _selectedViewController = selectedViewController; 
} 
 
// 切換操作(自定義的,聯(lián)想我在前面文章網(wǎng)易標簽欄切換中,系統(tǒng)給的transitionFromViewController,是一個道理) 
- (void)_transitionToChildViewController:(UIViewController *)toViewController 
{ 
    UIViewController *fromViewController = self.childViewControllers.count > 0 ? self.childViewControllers[0] : nil; 
    if (toViewController == fromViewController) { 
        return; 
    } 
    UIView *toView = toViewController.view; 
    [toView setTranslatesAutoresizingMaskIntoConstraints:YES]; 
    toView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight; 
    toView.frame = self.view.bounds; 
     
    // 自定義容器的切換,addChildViewController是關鍵,它保證了你想要顯示的VC能夠加載到容器中 
    // 而所謂的動畫和上下文,只是為了轉場的動畫效果 
    // 因此,就算用UIScrollView切換,也不能缺少addChildViewController,切記!切記! 
    [fromViewController willMoveToParentViewController:nil]; 
    [self addChildViewController:toViewController]; 
     
    if (!fromViewController) { 
        [self.view addSubview:toViewController.view]; 
        [toViewController didMoveToParentViewController:self]; 
        return; 
    } 
     
    // Animator 
    FTMthTransitionAnimator *transitionAnimator = [[FTMthTransitionAnimator alloc] init]; 
    NSUInteger fromIndex = [self.viewControllers indexOfObject:fromViewController]; 
    NSUInteger toIndex = [self.viewControllers indexOfObject:toViewController]; 
     
    // Context 
    FTMthTransitionContext *transitionContext = [[FTMthTransitionContext alloc] initWithFromViewController:fromViewController toViewController:toViewController goingRight:(toIndex > fromIndex)]; 
    transitionContext.animated = YES; 
    transitionContext.interactive = NO; 
    transitionContext.completionBlock = ^(BOOL didComplete) { 
        // 因為是非交互式,所以fromVC可以直接直接remove出its parent's children controllers array 
        [fromViewController.view removeFromSuperview]; 
        [fromViewController removeFromParentViewController]; 
        [toViewController didMoveToParentViewController:self]; 
        if ([transitionAnimator respondsToSelector:@selector (animationEnded:)]) { 
            [transitionAnimator animationEnded:didComplete]; 
        } 
    }; 
    // 轉場動畫需要以轉場上下文為依托,因為我們是自定義的Context,所以要手動設置 
    [transitionAnimator animateTransition:transitionContext]; 
}