NSURLConnection是2003年伴随着Safari一起发行的网络开发API,距今已经有十一年。当然,在这十一年间它表现的相当优秀,有大量的应用基础,这也是为什么前面花了那么长时间对它进行详细介绍的原因。但是这些年伴随着iPhone、iPad的发展,对于NSURLConnection设计理念也提出了新的挑战。在2013年WWDC上苹果揭开了NSURLSession的面纱,将它作为NSURLConnection的继任者。相比较NSURLConnection,NSURLSession提供了配置会话缓存、协议、cookie和证书能力,这使得网络架构和应用程序可以独立工作、互不干扰。另外,NSURLSession另一个重要的部分是会话任务,它负责加载数据,在客户端和服务器端进行文件的上传下载。
通过前面的介绍大家可以看到,NSURLConnection完成的三个主要任务:获取数据(通常是JSON、XML等)、文件上传、文件下载。其实在NSURLSession时代,他们分别由三个任务来完成:NSURLSessionData、NSURLSessionUploadTask、NSURLSessionDownloadTask,这三个类都是NSURLSessionTask这个抽象类的子类,相比直接使用NSURLConnection,NSURLSessionTask支持任务的暂停、取消和恢复,并且默认任务运行在其他非主线程中,具体关系图如下:
数据请求
前面通过请求一个微博数据进行数据请求演示,现在通过NSURLSessionDataTask实现这个功能,其实现流程与使用NSURLConnection的静态方法类似,下面是主要代码:
-(void)loadJsonData{ //1.创建url NSString *urlStr=[NSString stringWithFormat:@"http://192.168.1.208/ViewStatus.aspx?userName=%@&password=%@",@"KenshinCui",@"123"]; urlStr =[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]; NSURL *url=[NSURL URLWithString:urlStr]; //2.创建请求 NSURLRequest *request=[NSURLRequest requestWithURL:url]; //3.创建会话(这里使用了一个全局会话)并且启动任务 NSURLSession *session=[NSURLSession sharedSession]; //从会话创建任务 NSURLSessionDataTask *dataTask=[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { if (!error) { // NSString *dataStr=[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]; // NSLog(@"%@",dataStr);
//主线程中更新UI
dispatch_async(dispatch_get_main_queue(),^{
// 更新UI
});
}];
[dataTask resume];//恢复线程,启动任务}
GCD简单介绍
1.什么是GCD?
全称是Grand Central Dispatch,可译为“牛逼的中枢调度器”
纯C语言,提供了非常多强大的函数
2.GCD的优势
GCD是苹果公司为多核的并行运算提出的解决方案
GCD会自动利用更多的CPU内核(比如双核、四核)
GCD会自动管理线程的生命周期(创建线程、调度任务、销毁线程)
程序员只需要告诉GCD想要执行什么任务,不需要编写任何线程管理代码
3.提示
(1)GCD存在于libdispatch.dylib这个库中,这个调度库包含了GCD的所有的东西,但任何IOS程序,默认就加载了这个库,在程序运行的过程中会动态的加载这个库,不需要我们手动导入。
点击+按钮,可以导入框架。
(2)GCD是纯C语言的,因此我们在编写GCD相关代码的时候,面对的函数,而不是方法。
(3)GCD中的函数大多数都以dispatch开头。
二、任务和队列
GCD中有2个核心概念
(1)任务:执行什么操作
(2)队列:用来存放任务
GCD的使用就2个步骤
(1)定制任务
(2)确定想做的事情
将任务添加到队列中,GCD会自动将队列中的任务取出,放到对应的线程中执行
提示:任务的取出遵循队列的FIFO原则:先进先出,后进后出。
执行任务
1.GCD中有2个用来执行任务的函数
说明:把右边的参数(任务)提交给左边的参数(队列)进行执行。
(1)用同步的方式执行任务 dispatch_sync(dispatch_queue_t queue, dispatch_block_t block);
参数说明:
queue:队列
block:任务
(2)用异步的方式执行任务 dispatch_async(dispatch_queue_t queue, dispatch_block_t block);
2.同步和异步的区别
同步:在当前线程中执行
异步:在另一条线程中执行
队列
1.队列的类型
GCD的队列可以分为2大类型
(1)并发队列(Concurrent Dispatch Queue)
可以让多个任务并发(同时)执行(自动开启多个线程同时执行任务)并发功能只有在异步(dispatch_async)函数下才有效
2)串行队列(Serial Dispatch Queue)
让任务一个接着一个地执行(一个任务执行完毕后,再执行下一个任务)
2)串行队列(Serial Dispatch Queue)
让任务一个接着一个地执行(一个任务执行完毕后,再执行下一个任务)
3.串行队列
GCD中获得串行有2种途径
(1)使用dispatch_queue_create函数创建串行队列
dispatch_queue_t dispatch_queue_create(const char *label, dispatch_queue_attr_t attr); // 队列名称, 队列属性,一般用NULL即可
示例:
dispatch_queue_t queue = dispatch_queue_create(“wendingding”, NULL); // 创建
dispatch_release(queue); // 非ARC需要释放手动创建的队列
(2)使用主队列(跟主线程相关联的队列)
主队列是GCD自带的一种特殊的串行队列,放在主队列中的任务,都会放到主线程中执行
使用dispatch_get_main_queue()获得主队列
示例:
dispatch_queue_t queue = dispatch_get_main_queue();
4.并发队列
GCD默认已经提供了全局的并发队列,供整个应用使用,不需要手动创建
使用dispatch_get_global_queue函数获得全局的并发队列
dispatch_queue_t dispatch_get_global_queue(dispatch_queue_priority_t priority,unsigned long flags); // 此参数暂时无用,用0即可
示例:
这个参数是留给以后用的,暂时用不上,传个0。
第一个参数为优先级,这里选择默认的。获取一个全局的默认优先级的并发队列。
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得全局并发队列</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
说明:全局并发队列的优先级
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">define</span> DISPATCH_QUEUE_PRIORITY_HIGH 2 // 高</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">define</span> DISPATCH_QUEUE_PRIORITY_DEFAULT 0 // 默认(中)</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">define</span> DISPATCH_QUEUE_PRIORITY_LOW (-2) // 低</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">define</span> DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN // 后台</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li></ul>
5.各种队列的执行效果
代码示GCD例任务队列
用异步函数往并发队列中添加任务:
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"NYViewController.h"</span></span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NYViewController</span> ()</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NYViewController</span></span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)viewDidLoad { [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> viewDidLoad]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1.获得全局的并发队列</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.添加任务到队列中,就可以执行任务</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//异步函数:具备开启新线程的能力</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片1----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打印主线程</span> <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;">"主线程----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> mainThread]); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">24</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">25</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">26</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">27</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">28</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">29</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">30</span></li></ul>
总结:同时开启三个子线程
用异步函数往串行队列中添加任务
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;">- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)viewDidLoad { [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> viewDidLoad]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打印主线程</span> <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;">"主线程----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> mainThread]); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建串行队列</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue= dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wendingding"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//第一个参数为串行队列的名称,是c语言的字符串</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//第二个参数为队列的属性,一般来说串行队列不需要赋值任何属性,所以通常传空值(NULL)</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.添加任务到队列中执行</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片1----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//3.释放资源</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_release(queue);</span> }</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">24</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">25</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">26</span></li></ul>
总结:会开启线程,但是只开启一个线程
用同步函数往并发队列中添加任务
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 用同步函数往并发队列中添加任务 */</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)viewDidLoad { [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> viewDidLoad]; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打印主线程</span> <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;">"主线程----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> mainThread]); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建串行队列</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue= dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.添加任务到队列中执行</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片1----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片3----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); } </span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">24</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">25</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">26</span></li></ul>
总结:不会开启新的线程,并发队列失去了并发的功能
用同步函数往串行队列中添加任务
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** *用同步函数往串行队列中添加任务 */</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)viewDidLoad { [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> viewDidLoad]; <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;">"用同步函数往串行队列中添加任务"</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//打印主线程</span> <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;">"主线程----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> mainThread]); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建串行队列</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue= dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wendingding"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2.添加任务到队列中执行</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片1----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片2----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(queue, ^{ <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;">"下载图片3----%@"</span>,[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]); }); }</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">8</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">9</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">10</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">11</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">12</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">13</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">14</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">15</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">16</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">17</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">18</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">19</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">20</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">21</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">22</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">23</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">24</span></li></ul>
总结:不会开启新的线程
补充
补充:队列名称的作用:
将来调试的时候,可以看得出任务是在哪个队列中执行的。
说明:同步函数不具备开启线程的能力,无论是什么队列都不会开启线程;异步函数具备开启线程的能力,开启几条线程由队列决定(串行队列只会开启一条新的线程,并发队列会开启多条线程)。
同步函数
(1)并发队列:不会开线程
(2)串行队列:不会开线程
异步函数
(1)并发队列:能开启N条线程
(2)串行队列:开启1条线程
补充:
凡是函数中,各种函数名中带有create\copy\new\retain等字眼,都需要在不需要使用这个数据的时候进行release。
GCD的数据类型在ARC的环境下不需要再做release。
CF(core Foundation)的数据类型在ARC环境下还是需要做release。
异步函数具备开线程的能力,但不一定会开线程
GÇD需要掌握的(很重要)
1.队列和任务
1> 任务 :需要执行什么操作
* 用block来封装任务
2> 队列 :存放任务
* 全局的并发队列 : 可以让任务并发执行
<code class="hljs fix has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-attribute" style="box-sizing: border-box;">dispatch_queue_t queue </span>=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;"> dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
- 自己创建的串行队列 : 让任务一个接着一个执行
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"cn.heima.queue"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
- 主队列 : 让任务在主线程执行
<code class="hljs fix has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-attribute" style="box-sizing: border-box;">dispatch_queue_t queue </span>=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;"> dispatch_get_main_queue();</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
2.执行任务的函数
1> 同步执行 : 不具备开启新线程的能力
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>...</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
2> 异步执行 : 具备开启新线程的能力
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>...</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li></ul>
3.常见的组合(掌握)
1> dispatch_async + 全局并发队列
2> dispatch_async + 自己创建的串行队列
4.线程间的通信(掌握)
<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; 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; background: transparent;"><span style="font-family:Comic Sans MS;font-size:18px;">dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{ // 执行耗时的异步操作<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span> dispatch_async(dispatch_get_main_queue(), ^{ // 回到主线程,执行UI刷新操作 }); });</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; 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; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">1</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">2</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">3</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">4</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">5</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">6</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">7</span></li><li style="box-sizing: border-box; padding: 0px 5px;"><span style="font-family:Comic Sans MS;font-size:18px;">8</span></li></ul>
5.GCD的所有API都在libdispatch.dylib,Xcode会自动导入这个库
- 主头文件 : #import
6.延迟执行(掌握)
1> perform….
// 3秒后自动回到当前线程调用self的download:方法,并且传递参数:@”http://555.jpg”
[self performSelector:@selector(download:) withObject:@”http://555.jpg” afterDelay:3];
2> dispatch_after…
// 任务放到哪个队列中执行
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
double delay = 3; // 延迟多少秒
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC)), queue, ^{
// 3秒后需要执行的任务
});
7.一次性代码(掌握)
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// 这里面的代码,在程序运行过程中,永远只会执行1次
});