從iOS7開始颜曾，蘋果更新了自定義ViewController轉(zhuǎn)場(chǎng)的API褐健，這些新增的類和接口讓很多人困惑，望而卻步物蝙。本文就從這些API入口炎滞，讓讀者理清這些API錯(cuò)綜復(fù)雜的關(guān)系。
幾個(gè)protocol
講自定義轉(zhuǎn)場(chǎng)就離不開這幾個(gè)protocol：
UIViewControllerContextTransitioningUIViewControllerAnimatedTransitioningUIViewControllerInteractiveTransitioningUIViewControllerTransitioningDelegateUINavigationControllerDelegateUITabBarControllerDelegate
乍一看很多诬乞，其實(shí)很簡(jiǎn)單册赛，我們可以將其分為三類：
- 描述ViewController轉(zhuǎn)場(chǎng)的：
UIViewControllerTransitioningDelegate,UINavigationControllerDelegate,UITabBarControllerDelegate - 定義動(dòng)畫內(nèi)容的
UIViewControllerAnimatedTransitioning,UIViewControllerInteractiveTransitioning - 表示動(dòng)畫上下文的
UIViewControllerContextTransitioning
描述ViewController轉(zhuǎn)場(chǎng)的
細(xì)說之前先扯個(gè)蛋：
為什么蘋果要引入這一套API？因?yàn)樵趇OS7之前震嫉，做轉(zhuǎn)場(chǎng)動(dòng)畫很麻煩森瘪，要寫一大堆代碼在ViewController中。引入這一套API之后票堵，在豐富功能的同時(shí)極大程度地降低了代碼耦合扼睬，實(shí)現(xiàn)方式就是將之前在ViewController里面的代碼通過protocol分離了出來。
順著這個(gè)思路往下想悴势，實(shí)現(xiàn)自定義轉(zhuǎn)場(chǎng)動(dòng)畫首先需要找到ViewController的delegate窗宇。蘋果告訴我們切換ViewController有三種形式：UITabBarController內(nèi)部切換，UINavigationController切換特纤，present modal ViewController军俊。這三種方式是不是需要不同的protocol呢？
我們分別來看下：
-
UIViewControllerTransitioningDelegate自定義模態(tài)轉(zhuǎn)場(chǎng)動(dòng)畫時(shí)使用捧存。
設(shè)置UIViewController的屬性transitioningDelegate粪躬。
@property (nullable, nonatomic, weak) id <UIViewControllerTransitioningDelegate> transitioningDelegate -
UINavigationControllerDelegate自定義navigation轉(zhuǎn)場(chǎng)動(dòng)畫時(shí)使用。
設(shè)置UINavigationController的屬性delegate
@property(nullable, nonatomic, weak) id<UINavigationControllerDelegate> delegate -
UITabBarControllerDelegate自定義tab轉(zhuǎn)場(chǎng)動(dòng)畫時(shí)使用昔穴。
設(shè)置UITabBarController的屬性delegate
@property(nullable, nonatomic,weak) id<UITabBarControllerDelegate> delegate
實(shí)際上這三個(gè)protocol干的事情是一樣的短蜕，就是我們“扯淡”的內(nèi)容，只不過他們的應(yīng)用場(chǎng)景不同罷了傻咖。我們下面以UINavigationControllerDelegate為例朋魔，其他的類似。
定義動(dòng)畫內(nèi)容的
UINavigationControllerDelegate主要包含這兩個(gè)方法：
- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController NS_AVAILABLE_IOS(7_0);
- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
animationControllerForOperation:(UINavigationControllerOperation)operation
fromViewController:(UIViewController *)fromVC
toViewController:(UIViewController *)toVC NS_AVAILABLE_IOS(7_0);
兩個(gè)方法分別返回UIViewControllerInteractiveTransitioning和UIViewControllerAnimatedTransitioning卿操，它們的任務(wù)是描述動(dòng)畫行為（轉(zhuǎn)場(chǎng)動(dòng)畫如何執(zhí)行警检，就看它倆的）。
從名字可以看出害淤，這兩個(gè)protocol的區(qū)別在于是否是interactive的扇雕。如何理解？****interactive動(dòng)畫可以根據(jù)輸入信息的變化改變動(dòng)畫的進(jìn)程窥摄。****例如iOS系統(tǒng)為UINavigationController提供的默認(rèn)右滑退出手勢(shì)就是一個(gè)interactive 動(dòng)畫镶奉，整個(gè)動(dòng)畫的進(jìn)程由用戶手指的移動(dòng)距離控制。
我們來看下相對(duì)簡(jiǎn)單的UIViewControllerAnimatedTransitioning:
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
@optional
- (void)animationEnded:(BOOL) transitionCompleted;
transitionDuration返回動(dòng)畫的執(zhí)行時(shí)間，animateTransition處理具體的動(dòng)畫哨苛，animationEnded是optional鸽凶，大部分情況下不需要處理。
這里出現(xiàn)了我們要講的最后一個(gè)protocol：UIViewControllerContextTransitioning建峭。
表示動(dòng)畫上下文的
UIViewControllerContextTransitioning也是唯一一個(gè)不需要我們實(shí)現(xiàn)的protocol玻侥。
Do not adopt this protocol in your own classes, nor should you directly create objects that adopt this protocol.
UIViewControllerContextTransitioning提供了一系列方法，為interactive和非interactive動(dòng)畫提供上下文：
//轉(zhuǎn)場(chǎng)動(dòng)畫發(fā)生在該View中
- (nullable UIView *)containerView;
//上報(bào)動(dòng)畫執(zhí)行完畢
- (void)completeTransition:(BOOL)didComplete;
//根據(jù)key返回一個(gè)ViewController亿蒸。我們通過UITransitionContextFromViewControllerKey找到將被替換掉的ViewController凑兰，通過UITransitionContextToViewControllerKey找到將要顯示的ViewController
- (nullable __kindof UIViewController *)viewControllerForKey:(NSString *)key;
還有一些其他的方法，我們以后用到再說边锁。
下面我們通過一個(gè)簡(jiǎn)單的Demo串聯(lián)理解下姑食。
DEMO
這是一個(gè)縮放同時(shí)修改透明度的動(dòng)畫，我們來看下如何實(shí)現(xiàn)茅坛。
在上面的講解中矢门，我們通過倒推的方式來理解轉(zhuǎn)場(chǎng)動(dòng)畫中用到的protocol，在Demo 中灰蛙，我們會(huì)從創(chuàng)建動(dòng)畫開始。
第一步：創(chuàng)建動(dòng)畫
由上面的解析得知隔躲，動(dòng)畫是在UIViewControllerAnimatedTransitioning中定義的摩梧，所以我們首先創(chuàng)建實(shí)現(xiàn)UIViewControllerAnimatedTransitioning的對(duì)象：JLScaleTransition。
JLScaleTransition.h
@interface JLScaleTransition : NSObject<UIViewControllerAnimatedTransitioning>
@end
JLScaleTransition.m
@implementation JLScaleTransition
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext
{
return 0.5f;
}
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
UIViewController *toVC = (UIViewController*)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
UIViewController *fromVC = (UIViewController*)[transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
UIView * containerView = [transitionContext containerView];
UIView * fromView = fromVC.view;
UIView * toView = toVC.view;
[containerView addSubview:toView];
[[transitionContext containerView] bringSubviewToFront:fromView];
NSTimeInterval duration = [self transitionDuration:transitionContext];
[UIView animateWithDuration:duration animations:^{
fromView.alpha = 0.0;
fromView.transform = CGAffineTransformMakeScale(0.2, 0.2);
toView.alpha = 1.0;
} completion:^(BOOL finished) {
fromView.transform = CGAffineTransformMakeScale(1, 1);
[transitionContext completeTransition:YES];
}];
}
在animateTransition中宣旱，我們分別獲取兩個(gè)ViewController的view仅父，將toView添加到containerView中，然后執(zhí)行動(dòng)畫浑吟。為了理解containerView和fromView,toView的關(guān)系笙纤，我們添加幾個(gè)log來分析一下：
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
UIViewController *toVC = (UIViewController*)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
UIViewController *fromVC = (UIViewController*)[transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
UIView * containerView = [transitionContext containerView];
UIView * fromView = fromVC.view;
UIView * toView = toVC.view;
NSLog(@"startAnimation! fromView = %@", fromView);
NSLog(@"startAnimation! toView = %@", toView);
for(UIView * view in containerView.subviews){
NSLog(@"startAnimation! list container subviews: %@", view);
}
[containerView addSubview:toView];
[[transitionContext containerView] bringSubviewToFront:fromView];
NSTimeInterval duration = [self transitionDuration:transitionContext];
[UIView animateWithDuration:duration animations:^{
fromView.alpha = 0.0;
fromView.transform = CGAffineTransformMakeScale(0.2, 0.2);
toView.alpha = 1.0;
} completion:^(BOOL finished) {
fromView.transform = CGAffineTransformMakeScale(1, 1);
[transitionContext completeTransition:YES];
for(UIView * view in containerView.subviews){
NSLog(@"endAnimation! list container subviews: %@", view);
}
}];
}
運(yùn)行l(wèi)og如下：
2016-06-29 13:50:48.512 JLTransition[1970:177922] startAnimation! fromView = <UIView: 0x7aaef4e0; frame = (0 0; 320 568); autoresize = W+H; layer = <CALayer: 0x7aaef5a0>>
2016-06-29 13:50:48.513 JLTransition[1970:177922] startAnimation! toView = <UIView: 0x796ac5a0; frame = (0 0; 320 568); autoresize = W+H; layer = <CALayer: 0x796ac050>>
2016-06-29 13:50:48.513 JLTransition[1970:177922] startAnimation! list container subviews: <UIView: 0x7aaef4e0; frame = (0 0; 320 568); autoresize = W+H; layer = <CALayer: 0x7aaef5a0>>
2016-06-29 13:50:49.017 JLTransition[1970:177922] endAnimation! list container subviews: <UIView: 0x796ac5a0; frame = (0 0; 320 568); autoresize = W+H; layer = <CALayer: 0x796ac050>>
可見，轉(zhuǎn)場(chǎng)執(zhí)行的時(shí)候组力，containerView中只包含fromView省容，轉(zhuǎn)場(chǎng)動(dòng)畫執(zhí)行完畢之后，containerView會(huì)將fromView移除燎字。因?yàn)?code>containerView不負(fù)責(zé)toView的添加腥椒，所以我們需要主動(dòng)將toView添加到containerView中。
注意候衍！非interactive轉(zhuǎn)場(chǎng)中笼蛛，動(dòng)畫結(jié)束之后需要執(zhí)行
[transitionContext completeTransition:YES];（如果動(dòng)畫被取消，傳NO）蛉鹿；但是在interactive轉(zhuǎn)場(chǎng)中滨砍，動(dòng)畫是否結(jié)束是由外界控制的（用戶行為或者特定函數(shù)），需要在外部調(diào)用。
第二步：定義轉(zhuǎn)場(chǎng)
在第二部惋戏，我們需要實(shí)現(xiàn)UIViewControllerAnimatedTransitioning领追，并將第一步創(chuàng)建的JLScaleTransition對(duì)象返回。
JLScaleNavControlDelegate.h
@interface JLScaleNavControlDelegate : NSObject<UINavigationControllerDelegate>
@end
JLScaleNavControlDelegate.m
@implementation JLScaleNavControlDelegate
- (nullable id <UIViewControllerAnimatedTransitioning>) navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
return [JLScaleTransition new];
}
@end
這一步很簡(jiǎn)單日川，實(shí)現(xiàn)UIViewControllerAnimatedTransitioning對(duì)應(yīng)方法即可蔓腐。
第三步：設(shè)置轉(zhuǎn)場(chǎng)
設(shè)置轉(zhuǎn)場(chǎng)其實(shí)就是設(shè)置delegate（還記得我們“扯淡”的內(nèi)容吧）。
self.navigationController.delegate = id<UINavigationControllerDelegate>
self.transitioningDelegate = id<UIViewControllerTransitioningDelegate>
self.tabBarController.delegate = id<UITabBarControllerDelegate>
設(shè)置delegate有兩種方式：通過代碼龄句；通過StoryBoard回论。
通過代碼設(shè)置
@interface ViewController ()
@property (nonatomic, strong) JLScaleNavControlDelegate * scaleNavDelegate;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.scaleNavDelegate = [JLScaleNavControlDelegate new];
}
- (IBAction)triggerTransitionDelegate:(id)sender
{
self.navigationController.delegate = self.scaleNavDelegate;
[self.navigationController pushViewController:[TargetViewController new] animated:YES];
}
通過StoryBoard設(shè)置
在StoryBoard中為Navigation Bar添加一個(gè)Object，并且聲明為JLScaleNavControlDelegate（定義見上文）分歇。
按住control傀蓉，從navigation controller拖線置新添加的object，指定為delegate职抡。
NEXT
今天就到這里葬燎，源碼放在github，還包括一些復(fù)雜的動(dòng)畫缚甩，會(huì)持續(xù)更新谱净，后面有時(shí)間專門挑幾個(gè)效果牛逼的聊聊。
