iOS多线程 GCD

创建

dispatch_queue_t otherQ = dispatch_queue_create(“name”, NULL);//NULL默认串行队列

获取主队列

dispatch_queue_t mainQ = dispatch_get_main_queue();NSOperationQueue *mainQ = [NSOperationQueue mainQueue]; // for object-oriented APIs

插入代码块到队列

dispatch_queue_t queue = ...;dispatch_async(queue, ^{ });

向主队列插入方法

- (void)performSelectorOnMainThread:(SEL)aMethod                         withObject:(id)obj                     waitUntilDone:(BOOL)waitUntilDone; //相当于dispatch_async(dispatch_get_main_queue(), ^{ /* call aMethod */ });

示例 iOS API 使用多线程

在主线程

NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration      //delegate如果设置成self，会在下载时候一直得到下载信息。例如下载了多少字节，下载位置。但是此时只关心下载是否完成。所以设置nil。                                                       delegate:nil                                                 <span style="color:#ff0000;">delegateQueue:[NSOperationQueue mainQueue]];</span>  NSURLSessionDownloadTask *task;  task = [session downloadTaskWithRequest:request                        completionHandler:^(NSURL *localfile, NSURLResponse *response, NSErr or *error) {/* yes, can do UI things directly because this is called on the main queue */ }];  [task resume];

不在主线程

NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration]; <span style="color:#ff0000;">// no delegateQueue</span>  NSURLSessionDownloadTask *task;  task = [session downloadTaskWithRequest:request                        completionHandler:^(NSURL *localfile, NSURLResponse *response, NSError *error) {      dispatch_async(dispatch_get_main_queue(), ^{ /* do UI things */ });      or [self performSelectorOnMainThread:@selector(doUIthings) withObject:nil waitUntilDone:NO];  }];  [task resume];