@(iOS知行路)[源码阅读|iOS开发|NSNotification|iOS印象]
GLPubSub 是 NSNotificationCenter
的封装,目标是简化 iOS 开发中的发布订阅模式。该库通过添加 NSObject 的 Category,使得所有对象都可以方便地使用其订阅或发布通知。
源码阅读
- GLEvent 类,传递的事件对象,包含
事件名称
、事件发布者
、事件附带的额外数据
/**
`GLEvent` is the event object passed into handler block.
*/
@interface GLEvent : NSObject
/**
* Name of the event
*/
@property (nonatomic, copy) NSString *name;
/**
* The object triggering the event
*/
@property (nonatomic, retain) id obj;
/**
* Additional data of the event
*/
@property (nonatomic, retain) id data;
/**
* Init `GLEvent` with `name`, `obj` and `data`.
*
* @param name Name of the event
* @param obj The object triggering the event
* @param data Additional data of the event
*
* @return Initialized `GLEvent`
*/
- (id)initWithName:(NSString *)name obj:(id)obj data:(id)data;
@end
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- 通过为
NSObject
添加 Category,增加订阅/取消订阅
、发布
事件等方法,以及设置事件处理的处理队列
@interface NSObject (GLPubSub)
#pragma mark - Class Methods
/**
* Set the queue to handle events. If not set or set to `nil, events will be handled on the queue where the notification is posted. Otherwise, all the events will be handled on the set queue.
*
* @param queue The queue on which to handle events.
*/
+ (void)setPubSubQueue:(NSOperationQueue *)queue;
#pragma mark - Publish Methods
/**
* Publish an event without additional data.
*
* @param name Event name to publish.
*
* @see -publish:data:
*/
- (void)publish:(NSString *)name;
/**
* Publish an event with additional data.
*
* @param name Event name to publish.
* @param data Additional data.
*
* @see -publish:
*/
- (void)publish:(NSString *)name data:(id)data;
#pragma mark - Subscribe Methods with Selector
/**
* Subscribe an event with selector.
*
* @param eventName Event name to subscribe.
* @param selector Selector to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:obj:selector:
* @see -subscribeOnce:selector:
* @see -subscribeOnce:obj:selector:
*/
- (id)subscribe:(NSString *)eventName selector:(SEL)selector;
/**
* Subscribe an event from a specified object with selector.
*
* @param eventName Event name to subscribe.
* @param object Publisher to subscribe from.
* @param selector Selector to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:selector:
* @see -subscribeOnce:selector:
* @see -subscribeOnce:obj:selector:
*/
- (id)subscribe:(NSString *)eventName obj:(id)obj selector:(SEL)selector;
/**
* Subscribe an event only once with selector.
*
* @param eventName Event name to subscribe.
* @param selector Selector to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:selector:
* @see -subscribe:obj:selector:
* @see -subscribeOnce:obj:selector:
*/
- (id)subscribeOnce:(NSString *)eventName selector:(SEL)selector;
/**
* Subscribe an event from a specified object only once with selector.
*
* @param eventName Event name to subscribe.
* @param object Publisher to subscribe from.
* @param selector Selector to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:selector:
* @see -subscribe:obj:selector:
* @see -subscribeOnce:selector:
*/
- (id)subscribeOnce:(NSString *)eventName obj:(id)obj selector:(SEL)selector;
#pragma mark - Subscribe Methods with Handler Block
/**
* Subscribe an event with handler block.
*
* @param eventName Event name to subscribe.
* @param handler Handler block to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:obj:handler:
* @see -subscribeOnce:handler:
* @see -subscribeOnce:obj:handler:
*/
- (id)subscribe:(NSString *)eventName handler:(GLEventHandler)handler;
/**
* Subscribe an event from a specified object with handler block.
*
* @param eventName Event name to subscribe.
* @param obj Publisher to subscribe from.
* @param handler Handler block to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:handler:
* @see -subscribeOnce:handler:
* @see -subscribeOnce:obj:handler:
*/
- (id)subscribe:(NSString *)eventName obj:(id)obj handler:(GLEventHandler)handler;
/**
* Subscribe an event only once with handler block.
*
* @param eventName Event name to subscribe.
* @param handler Handler block to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:handler:
* @see -subscribe:obj:handler:
* @see -subscribeOnce:obj:handler:
*/
- (id)subscribeOnce:(NSString *)eventName handler:(GLEventHandler)handler;
/**
* Subscribe an event from a specified object only once with handler block.
*
* @param eventName Event name to subscribe.
* @param obj Publisher to subscribe from.
* @param handler Handler block to handle the event.
*
* @return An opaque object to act as the observer.
*
* @see -subscribe:handler:
* @see -subscribe:obj:handler:
* @see -subscribeOnce:handler:
*/
- (id)subscribeOnce:(NSString *)eventName obj:(id)obj handler:(GLEventHandler)handler;
#pragma mark - Unsubscribe Methods
/**
* Unsubscribe speficied event for current instance.
*
* @param eventName Name of event to unsubscribe.
*
* @see -unsubscribeAll
*/
- (void)unsubscribe:(NSString *)eventName;
/**
* Unsubscribe all events for current instance.
*
* @see -unsubscribe:
*/
- (void)unsubscribeAll;
@end
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- 发布事件的实现
- (void)publish:(NSString *)name data:(id)data {
// 通知中心发出通知,并将事件对象放入`userInfo`
NSDictionary *userInfo = nil;
if (data != nil) {
userInfo = @{kGLPubSubDataKey: data};
}
[[NSNotificationCenter defaultCenter] postNotificationName:name object:self userInfo:userInfo];
}
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- 订阅事件的实现
- (id)subscribe:(NSString *)eventName obj:(id)obj selector:(SEL)selector {
// 用于判断`selector`的参数个数
NSMethodSignature *sig = [self methodSignatureForSelector:selector];
// The hidden arguments self and _cmd (of type SEL) are at indices 0 and 1; method-specific arguments begin at index 2
BOOL passEventObj = ([sig numberOfArguments] == 3);
__weak __typeof__(self) weakSelf = self;
return [self subscribe:eventName obj:obj handler:^(GLEvent *event) {
__strong __typeof__(weakSelf) strongSelf = weakSelf;
if (passEventObj) {
[strongSelf performSelector:selector withObject:event];
} else {
[strongSelf performSelector:selector];
}
}];
}
- (id)subscribe:(NSString *)eventName obj:(id)obj handler:(GLEventHandler)handler {
// 通知中心通过添加观察者,并在block中生成事件进行转发
id observer = [[NSNotificationCenter defaultCenter] addObserverForName:eventName object:obj queue:_pubSubQueue usingBlock:^(NSNotification *note) {
GLEvent *event = [[GLEvent alloc] initWithName:eventName obj:note.object data:[note.userInfo objectForKey:kGLPubSubDataKey]];
handler(event);
}];
// 添加观察者对象至该事件的观察者数组,用于取消订阅事件
NSMutableDictionary *subscriptions = (NSMutableDictionary *)objc_getAssociatedObject(self, &kGLPubSubSubscriptionsKey);
if (!subscriptions) {
subscriptions = [[NSMutableDictionary alloc] init];
objc_setAssociatedObject(self, &kGLPubSubSubscriptionsKey, subscriptions, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
NSMutableSet *observers = [subscriptions objectForKey:eventName];
if (!observers) {
observers = [[NSMutableSet alloc] init];
[subscriptions setObject:observers forKey:eventName];
}
[observers addObject:observer];
return observer;
}
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- 取消事件的实现
- (void)unsubscribe:(NSString *)eventName {
NSMutableDictionary *subscriptions = (NSMutableDictionary *)objc_getAssociatedObject(self, &kGLPubSubSubscriptionsKey);
if (!subscriptions)
return;
NSMutableSet *observers = [subscriptions objectForKey:eventName];
if (observers) {
// 通知中心移除所有该事件的观察者
for (id observer in observers) {
[[NSNotificationCenter defaultCenter] removeObserver:observer];
}
// 订阅数组中移除该事件观察者数组对象
[subscriptions removeObjectForKey:eventName];
}
}
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附:安装与使用
CocoaPods
- 在
Podfile
里添加以下依赖:
pod "GLPubSub", "~> 1.0"
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- 运行
pod install
来安装 GLPubSub
源文件
如果你的项目没有用 CocoaPods 来管理第三方依赖,你也可以直接导入源文件。
- 下载最新代码并解压
- 导入
NSObject+GLPubSub.h
和NSObject+GLPubSub.m
到你的工程,记得在导入时勾选 "Copy items if needed"
因为 GLPubSub 是基于 NSNotificationCenter
并注册在 [NSNotificationCenter defaultCenter]
的,所以 GLPubSub 也支持大部分系统通知,例如 UIApplicationDidEnterBackgroundNotification
,UIApplicationDidBecomeActiveNotification
,UITextFieldTextDidChangeNotification
等等,但是转发的过程中会丢弃系统通知的 userInfo
字段。
设置 PubSub 的队列
GLPubSub 主要基于 NSNotificationCenter
的 -addObserverForName:object:queue:usingBlock:
方法。你可以调用 NSObject
的 +setPubSubQueue:
方法来设置传入该方法的 queue
。
默认传入的 queue
为 nil
,这意味着所有事件会在发布通知的线程中被执行。你可以手动设置为 [NSOperationQueue maniQueue]
使得所有事件在主线程被触发:
[NSObject setPubSubQueue:[NSOperationQueue mainQueue]];
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通过 Selector 订阅事件
大部分时候,我们用 self
作为订阅者:
[self subscribe:@"YourEventName" selector:@selector(yourEventHandler)];
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你也可以指定事件的发布者:
[self subscribe:@"YourEventName" obj:somePublisher selector:@selector(yourEventHandler)];
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如果你希望你的方法只触发一次,你可以用:
[self subscribeOnce:@"YourEventName" selector:@selector(yourEventHandler)];
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这样当该事件被触发后,就会自动取消订阅。
你的方法可以接受一个 GLEvent
参数,该参数包含了被触发事件的相关信息。
@interface GLEvent : NSObject
@property (nonatomic, copy) NSString *name;
@property (nonatomic, retain) id obj;
@property (nonatomic, retain) id data;
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name
是事件名,obj
是发布者,data
是附加信息。
通过 Block 订阅事件
方法与上面通过 selector 订阅的方法类似:
GLEventHandler
定义如下:
typedef void (^GLEventHandler)(GLEvent *event);
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所以你可以如下用 block 订阅一个事件:
__weak __typeof__(self) weakSelf = self;
[self subscribe:UIApplicationDidEnterBackgroundNotification handler:^(GLEvent *event) {
__strong __typeof__(weakSelf) strongSelf = weakSelf;
[strongSelf appDidEnterBackground];
}];
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这里的 weak 化是为了避免循环引用。对应于前面 selector 的方法,用 block 也有 4 种调用方法:
- (id)subscribe:(NSString *)eventName handler:(GLEventHandler)handler;
- (id)subscribe:(NSString *)eventName obj:(id)obj handler:(GLEventHandler)handler;
- (id)subscribeOnce:(NSString *)eventName handler:(GLEventHandler)handler;
- (id)subscribeOnce:(NSString *)eventName obj:(id)obj handler:(GLEventHandler)handler;
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取消订阅
取消订阅某个事件:
- (void)unsubscribe:(NSString *)eventName;
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取消订阅所有事件:
- (void)unsubscribeAll;
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虽然当实例被销毁时,存在 associated object 中的观察者也都会被销毁,但还是建议手动取消订阅,如根据不同需求,在 -dealloc
或 -viewDidDisappear
方法中取消订阅。
- (void)dealloc
{
[self unsubscribeAll];
}
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发布事件
你可以简单地发布一个事件:
[self publish:@"YourEventName"];
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也可以附带一些数据,很多时候我们会传入一个 NSDictionary
来附带更多结构化的数据:
[self publish:@"YourEventName" data:@{@"key": value}]
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循环引用
因为所有生成的观察者都会被 self
引用,所以当你的 block 引用 self
的时候就会形成循环引用导致实例无法被释放,所以你必须 weakify self
。强烈推荐用 libextobjc 中的 EXTScope 来做 weakify/strongify:
@weakify(self);
[self subscribe:UIApplicationDidEnterBackgroundNotification handler:^(GLEvent *event) {
@strongify(self);
[self appDidEnterBackground];
}];
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