NSNotificationCenter的使用
From:?http://blog.163.com/fuxiaohui@126/blog/static/131745826201196104455203/
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什么是Notification
? ? 这个要求其实也很容易实现.?每个运行中的application都有一个NSNotificationCenter的成员变量,它的功能就类似公共栏.?对象注册关注某个确定的notification(如果有人捡到一只小狗,就去告诉我).?我们把这些注册对象叫做observer.?其它的一些对象会给center发送notifications(我捡到了一只小狗). center将该notifications转发给所有注册对该notification感兴趣的对象.?我们把这些发送notification的对象叫做?poster
很多的标准Cocoa类会发送notifications:?在改变size的时候,Window会发送notification;?选择table view中的一行时,table view会发送notification;我们可以在在线帮助文档中查看到标准cocoa对象发送的notification
在对象释放前,我们必须从notification center移除我们注册的observer.?一般我们在dealloc方法中做这件事
NSNotification类
提供给observer的信息包裹. notification对象有两个重要的成员变量: name?和?object.
- (NSString?*)name;
- (id)object;
- (NSDictionary?*)userInfo;我们想要notification对象传递更多的信息
+ (id)notificationWithName:(NSString?*)aName object:(id)anObject;
+ (id)notificationWithName:(NSString?*)aName object:(id)anObject userInfo:(NSDictionary?*)aUserInfo;
NSNotificationCenter类
+ (id)defaultCenter;返回notification center [类方法,返回全局对象,?单件模式.cocoa的很多的全局对象都是通过类似方法实现]
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- (void)addObserver:(id)observer selector:(SEL)aSelector name:(NSString?*)aName object:(id)anObject;
?如果notificationName为nil.?那么notification center将anObject发送的所有notification转发给observer
.?如果anObject为nil.那么notification center将所有名字为notificationName的notification转发给observer
- (void)postNotification:(NSNotification?*)notification;
- (void)postNotificationName:(NSString?*)aName object:(id)anObject;
- (void)postNotificationName:(NSString?*)aName object:(id)anObject userInfo:(NSDictionary?*)aUserInfo;
- (void)removeObserver:(id)observer;
- (void)removeObserver:(id)observer name:(NSString?*)aName object:(id)anObject;
NSNotificationCenter 的使用方法举例（虚拟键盘的显示隐藏）
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1. 定义一个方法
update
2.订阅通知
?[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(update) name:@"update" object:nil]
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3. 在要发出通知消息的地方
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[[NSNotificationCenter defaultCenter] postNotificationName:@"update" object:nil];
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虚拟键盘显示和消失的通知
[[NSNotificationCenter defaultCenter] addObserver:self?selector:@selector(keyboardWasShown:)?name:UIKeyboardDidShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self?selector:@selector(keyboardWasHidden:)?name:UIKeyboardDidHideNotification
object:nil];
- (void)keyboardWasShown:(NSNotification *) aNotification{
if(keyboardShown)return;
NSDictionary *info = [aNotification userInfo];//获取通知信息
//get the size of the keyboard.
NSValue *aValue = [info objectForKey:UIKeyboardFrameBeginUserInfoKey];
CGSize keyboardSize = [aValue CGRectValue].size;
//Resize the scroll view
CGRect viewFrame = [scrollView frame];
viewFrame.size.height -= keyboardSize.height;
//Scroll the active text field into view
CGRect textFieldRect = [activeField frame];
[scrollView scrollRectToVisible:textFieldRect animated:YES];
keyboardShown = YES;
}
//Called when the UIKeyboardDidHideNotification is sent
- (void)keyboardWasHidden:(NSNotification *) aNotification{
NSDictionary *info = [aNotification userInfo];
//Get the size of the keyboard.
NSValue *aValue = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
CGSize keyboardSize = [aValue CGRectValue].size;
//Reset the height of the scroll view to its original value
CGRect viewFrame = [scrollView Frame];
viewFrame.size.height += keyboardSize.height;
scrollView.frame = viewFrame;
keyboardShown = NO;
}
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