在一個(gè)App中芋浮，彈窗一直是一個(gè)使用頻率較高的提示類控件兄世。蘋果對(duì)用戶體驗(yàn)方面的重視程度有多高甜孤，在彈窗的處理上就能體現(xiàn)出這一點(diǎn)來(lái)。不知你是否留意過(guò)新安裝的App上的彈窗顯示順序粥喜？通常是這樣的凸主，如果先出現(xiàn)的是通知權(quán)限彈窗然后是定位權(quán)限彈窗，前一個(gè)彈窗會(huì)暫時(shí)隱藏额湘，等用戶關(guān)掉后一個(gè)彈窗后才再次彈出來(lái)卿吐。顯然蘋果認(rèn)為后面的彈窗更重要，所以應(yīng)當(dāng)優(yōu)先被用戶處理锋华。蘋果對(duì)彈窗的彈出順序進(jìn)行了LIFO（last in, first out）后進(jìn)先出的管理嗡官。
本文后面會(huì)講解如何使用Runtime和多線程實(shí)現(xiàn)LIFO和FIFO （first in, last out）先進(jìn)先出。先看一下最終效果毯焕，這是一個(gè)自定義轉(zhuǎn)場(chǎng)動(dòng)畫（TransitionAnimation）的UIViewController衍腥。
UIAlertView支持自動(dòng)后進(jìn)先出管理。但是纳猫，它從iOS8開(kāi)始就已經(jīng)被廢棄了婆咸，再次使用UIAlertView，代碼中會(huì)出現(xiàn)黃色警告提示芜辕。以下是UIAlertView被廢棄的說(shuō)明尚骄，蘋果讓我們使用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是繼承于UIViewController并自定義了轉(zhuǎn)場(chǎng)動(dòng)畫的控制器侵续，和其它modal控制器一樣調(diào)用presentViewController:animated:completion:方法彈出倔丈。但是，每個(gè)控制器只能擁有一個(gè)presentedController询兴，也就是每次只能present一個(gè)別的控制器乃沙，強(qiáng)行present新的會(huì)出現(xiàn)以下提示：
Warning: Attempt to present <UIAlertController: 0x7fdb635045d0> on <ViewController: 0x7fdb660090f0> which is already presenting <UIAlertController: 0x7fdb635084a0>
很多情況下，異步請(qǐng)求結(jié)束后诗舰，我們需要根據(jù)服務(wù)器的返回信息進(jìn)行彈窗提示警儒。卻無(wú)法保證當(dāng)時(shí)的所在控制器是否已經(jīng)present了別的UIAlertController，新的彈窗是彈不出來(lái)的眶根。所以使用UIAlertController會(huì)給我們帶來(lái)很大的困擾蜀铲。
還有一種是把自定義的UIView蓋到UIWindow的方式進(jìn)行彈窗。首先這種方式不支持彈出順序管理属百，其次同時(shí)彈出多個(gè)就是多次執(zhí)行addSubview方法记劝，很多半透明背景遮罩和view疊加在一起，顯示效果不言而喻族扰。更重要的是厌丑，很多系統(tǒng)控件也使用了window作為父控件定欧，比如鍵盤的window是UITextEffectsWindow，頻繁使用window可能會(huì)出現(xiàn)很多意想不到的問(wèn)題怒竿。
總結(jié)一下上述3種彈窗方式：
| 彈窗方式 | 存在的問(wèn)題 |
|---|---|
| UIAlertView | iOS8開(kāi)始已經(jīng)被廢棄 |
| UIAlertController | 每次只能彈一個(gè) |
| -[UIWindow addSubview:] | 同時(shí)彈出多個(gè)的顯示效果較差 |
現(xiàn)在開(kāi)始講解如何用FIFO和LIFO管理modal控制器
先講相對(duì)簡(jiǎn)單的FIFO
效果如下
ps: gif圖中砍鸠，彈窗2的點(diǎn)擊事件中彈出彈窗4，觀察在FIFO和LIFO中的區(qū)別
首先耕驰，新建一個(gè)UIViewController的分類爷辱，設(shè)計(jì)成分類的目的是做到百分百解耦，供控制器調(diào)用朦肘，并支持對(duì)所有繼承于UIViewController的控制器進(jìn)行FIFO和LIFO的modal管理饭弓。
分類的頭文件只有一個(gè)方法，用來(lái)替代系統(tǒng)的presentViewController:animated:completion:方法媒抠。該方法接收一個(gè)UIViewController參數(shù)弟断，一個(gè)present完成的回調(diào)和dismiss完成的回調(diào)。
// 枚舉趴生，要用哪種方式管理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文件中夫嗓，方法的實(shí)現(xiàn)是這樣的
// 判斷JCPresentType枚舉類型，跳轉(zhuǎn)到具體方法
- (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單例冲秽，用于添加operation
- (NSOperationQueue *)getOperationQueue {
static NSOperationQueue *operationQueue = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
operationQueue = [NSOperationQueue new];
});
return operationQueue;
}
// 使用關(guān)聯(lián)對(duì)象存取deallocCompletion這個(gè)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方法舍咖，在這個(gè)時(shí)候調(diào)deallocCompletion這個(gè)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是多線程中的信號(hào)量，dispatch_semaphore_signal函數(shù)使信號(hào)量加一锉桑，dispatch_semaphore_wait使信號(hào)量減一排霉，并且在信號(hào)量小于0的時(shí)候暫停當(dāng)前線程。
presentViewController是一個(gè)耗時(shí)操作民轴，我把這個(gè)操作放在NSBlockOperation中攻柠，用dispatch_semaphore_t暫停線程直到present完成。并設(shè)置每個(gè)NSBlockOperation的前后依賴后裸，最后加到NSOperationQueue中瑰钮，組成一個(gè)串行的先進(jìn)先出隊(duì)列。
下面開(kāi)始講LIFO
效果如下
// 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];
}
// 使用關(guān)聯(lián)對(duì)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);
}
// 使用關(guān)聯(lián)對(duì)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);
}
// 使用關(guān)聯(lián)對(duì)象存取temporarilyDismissed微驶，用于判斷是臨時(shí)隱藏還是用戶關(guān)閉控制器
- (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];
}
// 使用關(guān)聯(lián)對(duì)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];
}
// 數(shù)組棧浪谴，用于緩存所有傳進(jìn)來(lái)的控制器
- (NSMutableArray *)getStackControllers {
static NSMutableArray *stackControllers = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
stackControllers = [NSMutableArray array];
});
return stackControllers;
}
// 臨時(shí)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方法的區(qū)別是，LIFO方法中因苹，每次進(jìn)來(lái)會(huì)先判斷前面是否已經(jīng)有控制器了苟耻，如果有就先臨時(shí)dismiss。并且扶檐，控制器在被用戶關(guān)閉的時(shí)候凶杖，優(yōu)先判斷棧后面有沒(méi)有還沒(méi)有彈出來(lái)的控制器，然后才判斷棧前面有沒(méi)有控制器款筑。
這樣智蝠，一個(gè)具有FIFO和LIFO驅(qū)動(dòng)的present分類方法就完成了腾么，敢緊試試吧。
