IOS开发基础篇--NSNotificationCenter使用小结

IOS开发基础篇--NSNotificationCenter使用小结

一、NSNotification和Delegate的联系和区别

众所周知，IOS中经常会使用到NSNotification和delegate来进行一些类之间的消息传递。言归正传，这两种有什么区别呢？

NSNotification就是IOS提供的一个消息中心，由一个全局的defaultNotification管理应用中的消息机制。通过公开的API可以看出，这里面使用了是一个观察者，通过注册addObserver和解除注册removeObserver来实现消息传递。苹果文档特别提出，在类析构的时候，要记得把removeObserver，不然就会引发崩溃，所以NSNotifcation的使用是没有retain+1的，NSNotification是一对多的。

至于Delegate，很简单，就是通过增加一个指针，然后把需要调用的函数通过delegate传递到其他类中，来得很直截了当。不需要通过广播的形式去实现，但是，delegate的形式只能是一对一，不能实现一对多。

在什么情况下使用Delegate和NSNotifiation呢?

从效率上看Delegate是一个很轻量级的，相对delegate，NSNotification却是一个很重量级的，效率上delegate明显要比Noticication高。一般情况我们会这样使用。

场景一：

A拥有B，然后B中的一些操作需要回调到A中，这时候就简单的通过delegate回调到A。因为B是A创建的，B可以很直接的把delegate赋值A。

场景二：

A和B是两个不相干的关系，A不知道B，B也不知道A，那么这时候如果通过delegate就没办法做到，会相对复杂。所以可以通过NSNotifcation去做一些消息传递。

所以使用delegate的情况是两者有直接的关系，至于一方知道另一方的存在。而NSNotifcation一般是大家不知道对方的存在，一般是使用跨模块的时候使用。在使用的时候，使用delegate可能需要多写一些delegate去实现，代码量比较多。NSNotication只要定义相关的NotificationName就可以很方便的沟通。两者各有所长。

二、监听系统自带的NSNotification

系统里定义了许多的 XxxNotification 名称，其实只要 Cmd+Shift+O 打开 Open Quickly，输入 NSNotification 或者 UINotification 可以看到许多以 Notification 结尾的变量定义，由变量名称也能理解在什么时候会激发什么事件，一般都是向 [NSNotificationCenter defaultCenter] 通知的。

使用步骤

第一步：注册系统监听事件

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;">    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在NSNotificationCenter中注册键盘弹出事件</span>
[[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotificationCenter</span> defaultCenter] addObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> selector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(keyboardUpEvent:) name:UIKeyboardDidShowNotification object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在NSNotificationCenter中注册键盘隐藏事件</span>
[[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotificationCenter</span> defaultCenter] addObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> selector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(keyboardDownEvent:) name:UIKeyboardDidHideNotification object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//在NSNotificationCenter中注册程序从后台唤醒事件</span>
[[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotificationCenter</span> defaultCenter] addObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> selector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(becomeActive:) name:UIApplicationDidBecomeActiveNotification object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

第二步：事件触发后的处理

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
*  弹出键盘事件触发处理
*
* <span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> notification
*/</span>
-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)keyboardUpEvent : (NSNotification *)notification{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NSLog(@"键盘弹出事件触发==%@",notification);</span>
NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"键盘弹出事件触发"</span>);
}

<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
*  键盘隐藏事件触发处理
*
* <span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> notification
*/</span>
-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)keyboardDownEvent : (NSNotification *)notification{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//NSLog(@"键盘隐藏事件触发==%@",notification);</span>
NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"键盘隐藏事件触发"</span>);
}

<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
*  程序从后台唤醒触发处理
*
* <span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> notification
*/</span>
-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)becomeActive: (NSNotification *)notification{
NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"程序从后台唤醒触发处理"</span>);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>

第三步、在dealloc中解除监听

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
*NSNotificationCenter 注意点：每一次在接受者对象中需要delleac把它销毁掉。
*/</span>
-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)dealloc{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

三、自定义NSNotification

这里我使用的一个实例为：在ViewController中定义一个按钮，点击该按钮，同时改变两个自定义View中的内容。

使用步骤

第一步、在ViewController中生成一个按钮，两个自定义View

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;">    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIButton</span> *postMsgBtn = [[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIButton</span> alloc] initWithFrame:CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">40</span>)];
[postMsgBtn setTitle:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"发送消息"</span> forState:UIControlStateNormal];
postMsgBtn<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.backgroundColor</span> = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIColor</span> grayColor];
[postMsgBtn addTarget:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> action:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(postMsg:) forControlEvents:UIControlEventTouchUpInside];
[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.view</span> addSubview:postMsgBtn];

MyView *view = [[MyView alloc] initWithFrame:CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">250</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span>)];
[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.view</span> addSubview:view];

MyView *view2 = [[MyView alloc] initWithFrame:CGRectMake(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">320</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span>)];
[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.view</span> addSubview:view2];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

第二步、点击按钮，发送Notification

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;">-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)postMsg: (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">UIButton</span> *)btn{
[[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotificationCenter</span> defaultCenter] postNotificationName:NOTIFICATION_MESSAGE_NAME object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span> userInfo:@{@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"jingming1"</span>}];
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

第三步、在自定义View中注册监听事件

<code class="hljs css has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;"><span class="hljs-attr_selector" style="color: rgb(0, 136, 0); box-sizing: border-box;">[[NSNotificationCenter defaultCenter]</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">addObserver</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:self</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">selector</span>:<span class="hljs-at_rule" style="box-sizing: border-box;">@<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">selector(acceptMsg:)</span> name:NOTIFICATION_MESSAGE_NAME object:nil]</span>;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

第四步、处理监听事件

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;">-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)acceptMsg : (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotification</span> *)notification{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>,notification);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span> *userInfo = notification<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.userInfo</span>;
_label<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.text</span> = [userInfo objectForKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>];
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

第五步、在dealloc中解除监听

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal;">-(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)dealloc{
[[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSNotificationCenter</span> defaultCenter] removeObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>];
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

四、参考文献

本来想自己总结文字写的，鉴于自己时间有限，而且网上有些博客总结也挺不错的，跟自己的想法很符合。所以有些就把别人的知识成果搬过来了，在次声明一下。

http://m.blog.csdn.net/blog/hzhenx1989/20217387

http://www.cnblogs.com/wenxp2006/articles/2499330.html

五、博主的话

以前看过很多别人的博客，学到不少东西。现在准备自己也开始写写博客，希望能够帮到一些人。

联系方式：

微博：新浪微博

博客：http://blog.csdn.net/yixiangboy

github：https://github.com/yixiangboy