在一个App中,弹窗一直是一个使用频率较高的提示类控件。它看似简单,却有很多高深的东西值得我们学习。
众所周知,苹果对用户体验方面的重视程度有多高,在弹窗的处理上就能体现出这一点来。不知你是否留意过新安装的App上的弹窗显示顺序?通常是这样的,如果先出现的是通知权限弹窗然后是定位权限弹窗,前一个弹窗会暂时隐藏,等用户关掉后一个弹窗后才再次弹出来。显然苹果认为后面的弹窗更重要,所以应当优先被用户处理。苹果对弹窗的弹出顺序进行了LIFO(last in, first out)后进先出的管理。
本文后面会讲解如何使用Runtime和多线程实现LIFO和FIFO (first in, last out)先进先出。先看一下最终效果,这是一个自定义转场动画(TransitionAnimation)的UIViewController。
最终效果
UIAlertView支持自动后进先出管理。但是,它从iOS8开始就已经被废弃了,再次使用UIAlertView,代码中会出现黄色警告提示。以下是UIAlertView被废弃的说明,苹果让我们使用UIAlertController去替代前者。
UIAlert View is deprecated in iOS 8. (Note that UIAlert View Delegate is also deprecated.) To create and manage alerts in iOS 8 and later, instead use UIAlert Controller with a preferred Style of UIAlert Controller Style Alert.
UIAlertController是继承于UIViewController并自定义了转场动画的控制器,和其它modal控制器一样调用presentViewController:animated:completion:方法弹出。但是,每个控制器只能拥有一个presentedController,也就是每次只能present一个别的控制器,强行present新的会出现以下提示:
Warning: Attempt to present on which is already presenting
很多情况下,异步请求结束后,我们需要根据服务器的返回信息进行弹窗提示。却无法保证当时的所在控制器是否已经present了别的UIAlertController,新的弹窗是弹不出来的。所以使用UIAlertController会给我们带来很大的困扰。
还有一种是把自定义的UIView盖到UIWindow的方式进行弹窗。首先这种方式不支持弹出顺序管理,其次同时弹出多个就是多次执行addSubview方法,很多半透明背景遮罩和view叠加在一起,显示效果不言而喻。更重要的是,很多系统控件也使用了window作为父控件,比如键盘的window是UITextEffectsWindow,频繁使用window可能会出现很多意想不到的问题。
总结一下上述3种弹窗方式:
现在开始讲解如何用FIFO和LIFO管理modal控制器
先讲相对简单的FIFO
FIFO流程图
效果如下
ps: gif图中,弹窗2的点击事件中弹出弹窗4,观察在FIFO和LIFO中的区别
自定义UIViewController
JCAlertController
首先,新建一个UIViewController的分类,设计成分类的目的是做到百分百解耦,供控制器调用,并支持对所有继承于UIViewController的控制器进行FIFO和LIFO的modal管理。
分类的头文件只有一个方法,用来替代系统的presentViewController:animated:completion:方法。该方法接收一个UIViewController参数,一个present完成的回调和dismiss完成的回调。
// 枚举,要用哪种方式管理modal控制器 typedef NS_OPTIONS (NSUInteger, JCPresentType) { JCPresentTypeLIFO = 0, // last in, first out JCPresentTypeFIFO // first in, last out };
// 新的present方法 - (void)jc_presentViewController:(UIViewController *)controller presentType:(JCPresentType)presentType presentCompletion:(void (^)(void))presentCompletion dismissCompletion:(void (^)(void))dismissCompletion;
.m文件中,方法的实现是这样的
// 判断JCPresentType枚举类型,跳转到具体方法 - (void)jc_presentViewController:(UIViewController *)controller presentType:(JCPresentType)presentType presentCompletion:(void (^)(void))presentCompletion dismissCompletion:(void (^)(void))dismissCompletion { if (presentType == JCPresentTypeLIFO) { [self lifoPresentViewController:controller presentCompletion:presentCompletion dismissCompletion:dismissCompletion]; } else { [self fifoPresentViewController:controller presentCompletion:presentCompletion dismissCompletion:dismissCompletion]; } }
// 核心方法 - (void)fifoPresentViewController:(UIViewController *)controller presentCompletion:(void (^)(void))presentCompletion dismissCompletion:(void (^)(void))dismissCompletion { dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ [controller setDeallocCompletion:^{ if (dismissCompletion) { dismissCompletion(); } // got to next operation dispatch_semaphore_signal(semaphore); }]; dispatch_async(dispatch_get_main_queue(), ^{ [self presentViewController:controller animated:YES completion:presentCompletion]; }); dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); }]; // put in queue if ([self getOperationQueue].operations.lastObject) { [operation addDependency:[self getOperationQueue].operations.lastObject]; } [[self getOperationQueue] addOperation:operation]; }
// NSOperationQueue单例,用于添加operation - (NSOperationQueue *)getOperationQueue { static NSOperationQueue *operationQueue = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ operationQueue = [NSOperationQueue new]; }); return operationQueue; }
// 使用关联对象存取deallocCompletion这个block - (void)setDeallocCompletion:(void (^)(void))completion { objc_setAssociatedObject(self, @selector(getDeallocCompletion), completion, OBJC_ASSOCIATION_COPY_NONATOMIC); } - (void (^)(void))getDeallocCompletion { return objc_getAssociatedObject(self, _cmd); }
// hook控制器的viewDidDisappear方法,在这个时候调deallocCompletion这个block + (void)load { SEL oldSel = @selector(viewDidDisappear:); SEL newSel = @selector(jc_viewDidDisappear:); Method oldMethod = class_getInstanceMethod([self class], oldSel); Method newMethod = class_getInstanceMethod([self class], newSel); BOOL didAddMethod = class_addMethod(self, oldSel, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)); if (didAddMethod) { class_replaceMethod(self, newSel, method_getImplementation(oldMethod), method_getTypeEncoding(oldMethod)); } else { method_exchangeImplementations(oldMethod, newMethod); } } - (void)jc_viewDidDisappear:(BOOL)animated { [self jc_viewDidDisappear:animated]; if ([self getDeallocCompletion] && ![self isTemporarilyDismissed]) { [self getDeallocCompletion](); } }
其中dispatch_semaphore_t是多线程中的信号量,dispatch_semaphore_signal函数使信号量加一,dispatch_semaphore_wait使信号量减一,并且在信号量小于0的时候暂停当前线程。
presentViewController是一个耗时操作,我把这个操作放在NSBlockOperation中,用dispatch_semaphore_t暂停线程直到present完成。并设置每个NSBlockOperation的前后依赖,最后加到NSOperationQueue中,组成一个串行的先进先出队列。
下面开始讲LIFO
LIFO流程图
效果如下
自定义UIViewController
JCAlertController
// 核心方法 - (void)lifoPresentViewController:(UIViewController *)controller presentCompletion:(void (^)(void))presentCompletion dismissCompletion:(void (^)(void))dismissCompletion { dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); // put in stack NSMutableArray *stackControllers = [self getStackControllers]; if (![stackControllers containsObject:controller]) { [stackControllers addObject:controller]; } NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ __weak typeof(controller) weakController = controller; [controller setPresentCompletion:presentCompletion]; [controller setDismissCompletion:dismissCompletion]; [controller setDeallocCompletion:^{ if (dismissCompletion) { dismissCompletion(); } // fetch new next controller if exists, because button action after dismiss completion [weakController setDismissing:YES]; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(CGFLOAT_MIN * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ [weakController setDismissing:NO]; // if the dismiss controller is the last one if (stackControllers.lastObject == controller) { [stackControllers removeObject:weakController]; // is there any previous controllers if (stackControllers.count > 0) { UIViewController *preController = [stackControllers lastObject]; [self lifoPresentViewController:preController presentCompletion:[preController getPresentCompletion] dismissCompletion:[preController getDismissCompletion]]; } } else { NSUInteger index = [stackControllers indexOfObject:weakController]; [stackControllers removeObject:weakController]; // is there any next controllers NSArray *nextControllers = [stackControllers objectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(index, stackControllers.count - index)]]; for (UIViewController *nextController in nextControllers) { [self lifoPresentViewController:nextController presentCompletion:[nextController getPresentCompletion] dismissCompletion:[nextController getDismissCompletion]]; } } }); }]; // if the previous controller is dismissing, wait it's completion if (stackControllers.count > 1) { for (UIViewController *preController in stackControllers) { if ([preController isDismissing]) { return ; } } } // present a new controller before dismissing the presented controller if exists dispatch_async(dispatch_get_main_queue(), ^{ if (self.presentedViewController) { [self.presentedViewController temporarilyDismissViewControllerAnimated:YES completion:^{ [self presentViewController:controller animated:YES completion:^{ dispatch_semaphore_signal(semaphore); }]; }]; } else { [self presentViewController:controller animated:YES completion:^{ dispatch_semaphore_signal(semaphore); if (presentCompletion) { presentCompletion(); } }]; } }); dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); }]; // put in queue if ([self getOperationQueue].operations.lastObject) { [operation addDependency:[self getOperationQueue].operations.lastObject]; } [[self getOperationQueue] addOperation:operation]; }
// 使用关联对象存取dismissCompletion - (void)setDismissCompletion:(void (^)(void))completion { objc_setAssociatedObject(self, @selector(getDismissCompletion), completion, OBJC_ASSOCIATION_COPY_NONATOMIC); } - (void (^)(void))getDismissCompletion { return objc_getAssociatedObject(self, _cmd); } // 使用关联对象存取presentCompletion - (void)setPresentCompletion:(void (^)(void))completion { objc_setAssociatedObject(self, @selector(getPresentCompletion), completion, OBJC_ASSOCIATION_COPY_NONATOMIC); } - (void (^)(void))getPresentCompletion { return objc_getAssociatedObject(self, _cmd); } // 使用关联对象存取temporarilyDismissed,用于判断是临时隐藏还是用户关闭控制器 - (void)setTemporarilyDismissed:(BOOL)temporarilyDismissed { objc_setAssociatedObject(self, @selector(isTemporarilyDismissed), @(temporarilyDismissed), OBJC_ASSOCIATION_RETAIN_NONATOMIC); } - (BOOL)isTemporarilyDismissed { NSNumber *num = objc_getAssociatedObject(self, _cmd); return [num boolValue]; } // 使用关联对象存取dismissing - (void)setDismissing:(BOOL)dismissing { objc_setAssociatedObject(self, @selector(isDismissing), @(dismissing), OBJC_ASSOCIATION_RETAIN_NONATOMIC); } - (BOOL)isDismissing { NSNumber *num = objc_getAssociatedObject(self, _cmd); return [num boolValue]; } // 数组栈,用于缓存所有传进来的控制器 - (NSMutableArray *)getStackControllers { static NSMutableArray *stackControllers = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ stackControllers = [NSMutableArray array]; }); return stackControllers; } // 临时dismiss方法 - (void)temporarilyDismissViewControllerAnimated: (BOOL)flag completion: (void (^ __nullable)(void))completion { [self setTemporarilyDismissed:YES]; [self dismissViewControllerAnimated:flag completion:^{ [self setTemporarilyDismissed:NO]; if (completion) { completion(); } }]; }
和FIFO方法的区别是,LIFO方法中,每次进来会先判断前面是否已经有控制器了,如果有就先临时dismiss。并且,控制器在被用户关闭的时候,优先判断栈后面有没有还没有弹出来的控制器,然后才判断栈前面有没有控制器。
这样,一个具有FIFO和LIFO驱动的present分类方法就完成了,敢紧试试吧。
下载地址:UIViewController+JCPresentQueue.h
参考资料