Agents and Notifications

Procedures for using agents and notification agents

• Define an agent Agreement
  • The format of the protocol name is generally: class name + Delegate
    • Like Uitableviewdelegate.
  • Proxy method Details
    • It's usually @optional.
    • Method names usually start with the class name
      • Like what- (void)scrollViewDidScroll:
    • It's usually necessary to pass the object itself out.
      • For example, TableView's method will pass the tableview itself out.
  • Must adhere to the NSObject agreement
    • Like what@protocol XMGWineCellDelegate <NSObject>
• Declaring a proxy property
  • Type of proxy format:id< Protocol > delegate

@property (nonatomic, weak) id<XMGWineCellDelegate> delegate;

• Set proxy Object

xxx.delegate = yyy;

• The proxy object adheres to the protocol and implements the corresponding method within the protocol.

• When something happens inside the control, you can call the agent's proxy method to notify the agent

  • If the proxy method is @optional, then you need to determine if the method is implemented

if ([self.delegate respondsToSelector:@selector(wineCellDidClickPlusButton:)]) {    [self.delegate wineCellDidClickPlusButton:self];}

Notice

• Announcement of the notification (publisher)
• Monitoring of notifications (listeners)
• Removal of notifications

Notification Center (Nsnottificationcenter)

• Each application has a notification hubs (Nsnotificationcenter) instance that is specifically designed to assist message communication between different objects
• any object can publish notifications (nsnotification) to the notification hub, Describe what you are doing. Other objects of interest (Observer) can request to receive this notification when a particular notification is published (or when a specific object is published)

//a complete notification generally contains 3 attributes:-(nsstring *) name; //Notification name-(id) object; //notifies the publisher (who wants to publish the notice)-(nsdictionary *) userInfo; //Some additional information (informing the publisher of the content delivered to the notification recipient) //initialize a notification (nsnotification) object + ( Instancetype) Notificationwithname: (nsstring *) AName object: ( id) anobject;+ (instancetype) Notificationwithname: ( NSString *) AName object: (id) anobject userInfo: ( Nsdictionary *) auserinfo;-(instancetype) Initwithname: (nsstring *) Name object: (id) object UserInfo: (nsdictionary *) userInfo;     

Publish Notifications

- (void)postNotification:(NSNotification *)notification;发布一个notification通知，可在notification对象中设置通知的名称、通知发布者、额外信息等- (void)postNotificationName:(NSString *)aName object:(id)anObject;发布一个名称为aName的通知，anObject为这个通知的发布者- (void)postNotificationName:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo;发布一个名称为aName的通知，anObject为这个通知的发布者，aUserInfo为额外信息

Registering a notification listener

/*observer：监听器，即谁要接收这个通知aSelector：收到通知后，回调监听器的这个方法，并且把通知对象当做参数传入aName：通知的名称。如果为nil，那么无论通知的名称是什么，监听器都能收到这个通知anObject：通知发布者。如果为anObject和aName都为nil，监听器都收到所有的通知*/- (void)addObserver:(id)observer selector:(SEL)aSelector name:(NSString *)aName object:(id)anObject;

Unregister Notification Listener

• Notification hubs does not hold (retain) listener objects, and objects registered in the notification hub must be unregistered before the object is released. Otherwise, the notification hub will still send a message to the listener when the corresponding notification appears again. The application may crash because the listener object has been freed

• Notification hubs provides the appropriate method to unregister listeners

- (void)removeObserver:(id)observer;- (void)removeObserver:(id)observer name:(NSString *)aName object:(id)anObject;//一般在监听器销毁之前取消注册（如在监听器中加入下列代码）：- (void)dealloc { //[super dealloc]; 非ARC中需要调用此句 [[NSNotificationCenter defaultCenter] removeObserver:self];}

Example of a notification (code)

• AAA is to inform the issuer that AAA is the listener

//aaa监听AAA的<军事新闻>通知[[NSNotificationCenter defaultCenter] addObserver:aaa selector:@selector(gotNews:) name:@"军事新闻" object:AAA];//AAA发布<军事新闻通知>[[NSNotificationCenter defaultCenter] postNotificationName:@"军事新闻" object:AAA userInfo:@{@"title" : @"453543"}];//销毁aaa监听者[[NSNotificationCenter defaultCenter] removeObserver:aaa];

How iOS listens to certain events

• Notice (nsnotificationcenter\nsnotification)
  • Messages can be passed between any object
  • Scope of Use
    • 1 objects can be notified to n objects
    • 1 objects can accept notifications from n objects
  • Must be guaranteed that the name of the notification is consistent when it is issued and monitored.
• KVO
  • Only the ability to listen to changes in object properties (less flexible than notifications and proxies)
• Agent
  • Scope of Use
    • 1 objects can only be set one proxy (assuming that the object has only 1 proxy properties)
    • 1 objects can be proxies for multiple objects
  • than the 通知 specification
  • It is recommended to use 代理 more通知

Agents and Notifications