GCD常用總結(jié)

  • 線程通訊
      //獲取全局隊列
        dispatch_queue_t queue=dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
        //封裝任務(wù)，將任務(wù)添加到隊列中
        dispatch_async(queue, ^{
            NSLog(@"執(zhí)行任務(wù)%@",[NSThread currentThread]);
            //回到主線程刷新任務(wù)
            dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"刷新UI%@",[NSThread currentThread]);
            });
        });
       //異步函數(shù)并不需要馬上執(zhí)行任務(wù)，不會阻塞線程。（先執(zhí)行NSLog后再回頭執(zhí)行block里的任物）
        NSLog(@"異步多線程");
  • 一次性代碼
 //整個程序運行過程中，只會執(zhí)行一次,開發(fā)實用場景：單例
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
        NSLog(@"一次性代碼");
        });
  • 延遲執(zhí)行
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), queue, ^{
        NSLog(@"延遲執(zhí)行%@",[NSThread currentThread]);
    });
    NSLog(@"異步多線程");
  • 柵欄函數(shù)
    //注意:柵欄函數(shù)不能使用全局并發(fā)隊列
    dispatch_queue_t queue = dispatch_queue_create("download", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"任務(wù)一-%@",[NSThread currentThread]);
     
    });
    dispatch_async(queue, ^{
        NSLog(@"任務(wù)二-%@",[NSThread currentThread]);
        
    });
    //柵欄函數(shù)
    //柵欄函數(shù)之前隊列中的任務(wù)執(zhí)行完畢之后才會執(zhí)行，柵欄函數(shù)之后之隊列中的任務(wù))，但不阻塞線程是異步的
    dispatch_barrier_async(queue, ^{
        
        NSLog(@"我是柵欄函數(shù)");
    });
    NSLog(@"異步函數(shù)1");
    dispatch_async(queue, ^{
        NSLog(@"任務(wù)三-%@",[NSThread currentThread]);
        
    });
        NSLog(@"異步函數(shù)2");
    ```
- 隊列組
    ```
   //1.封裝任務(wù)，將任務(wù)添加隊列中，監(jiān)聽隊列的執(zhí)行情況
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_group_t group= dispatch_group_create();

    //下載圖片一
    dispatch_group_async(group, queue, ^{
        NSURL *url=[NSURL URLWithString:@"http://xo7788.com/uploads/allimg/160727/1130119505_0.jpg"];
        NSData *imageData=[NSData dataWithContentsOfURL:url];
        self.image1=[UIImage imageWithData:imageData];

   //下載圖片二
    dispatch_group_async(group, queue, ^{
        NSURL *url=[NSURL URLWithString:@"http://pic.58pic.com/58pic/17/41/38/88658PICNuP_1024.jpg"];
        NSData *imageData=[NSData dataWithContentsOfURL:url];
        self.image2=[UIImage imageWithData:imageData];

    });
    
   //下載圖片三
    dispatch_group_async(group, queue, ^{
         NSURL *url=[NSURL URLWithString:@"http://pic.58pic.com/58pic/17/41/38/88658PICNuP_1024.jpg"];
        NSData *imageData=[NSData dataWithContentsOfURL:url];
        self.image2=[UIImage imageWithData:imageData];

    });

   //合并圖片
    //攔截通知，當(dāng)隊列組的所有任務(wù)完全，執(zhí)行完后會進入下面的方法
    //該方法本身是異步的
    dispatch_group_notify(group, queue, ^{
  //3.1 創(chuàng)建圖形上下文
        UIGraphicsBeginImageContext(CGSizeMake(200, 200));
        
        //3.2 畫圖1
        [self.image1 drawInRect:CGRectMake(0, 0, 200, 100)];
        self.image1 = nil;
      
        //3.3 畫圖2
        [self.image2 drawInRect:CGRectMake(0, 100, 200, 100)];
        self.image2 = nil;
        
        //3.4 根據(jù)上下文得到一張圖片
        UIImage *image =  UIGraphicsGetImageFromCurrentImageContext();
        
        //3.5 關(guān)閉上下文
        UIGraphicsEndImageContext();
        NSLog(@"%@合并",[NSThread currentThread]);
        dispatch_async(dispatch_get_main_queue(), ^{
            self.imageview.image=image;
        });
    });
    NSLog(@"異步函數(shù)");
     ```

- 多網(wǎng)絡(luò)請求 (GCD信號量)
參考學(xué)習(xí)文章：http://www.itdecent.cn/p/c194ca08776c
開發(fā)需求01：一個很常見的需求：項目中的業(yè)務(wù)接口請求的時候需要Token驗證。我們最簡化這個需求就是：兩個請求，請求1成功返回所需參數(shù)之后，才能開始請求2。
  • (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //創(chuàng)建一個并行隊列
    dispatch_queue_t queque = dispatch_queue_create("GoyakodCreated", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queque, ^{
    [self request1];
    [self request2];
    });
    //注意這是請求不能放在主線程上，要不然，AFN的block回掉回造成線程死鎖
    }

  • (void)request1{
    //01創(chuàng)建信號量并設(shè)置計數(shù)默認為0
    dispatch_semaphore_t sema = dispatch_semaphore_create(0);
    //1.創(chuàng)建會話管理者
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

    //注意:如果返回的是xml數(shù)據(jù),那么應(yīng)該修改AFN的解析方案AFXMLParserResponseSerializer
    //注意:如果返回的數(shù)據(jù)既不是xml也不是json那么應(yīng)該修改解析方案為:
    //manager.responseSerializer = [AFXMLParserResponseSerializer serializer];

    //告訴AFN能夠接受text/html類型的數(shù)據(jù)
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/html"];

    manager.responseSerializer = [AFHTTPResponseSerializer serializer];

    //2.發(fā)送GET請求
    [manager GET:@"http://www.baidu.com" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task,id _Nullable responseObject) {

         //02發(fā)送信號量計數(shù)+1
     dispatch_semaphore_signal(sema);
    NSLog(@"網(wǎng)絡(luò)請求1");
  //UIImage *image = [UIImage imageWithData:responseObject];
  NSLog(@"block-%@",[NSThread currentThread]);

    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
    dispatch_semaphore_signal(sema);
    NSLog(@"請求失敗--%@",error);
    }];

    //若計數(shù)為0則一直等待
    dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);

}

  • (void)request2{

      //1.創(chuàng)建會話管理者
  AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
  
  //注意:如果返回的是xml數(shù)據(jù),那么應(yīng)該修改AFN的解析方案AFXMLParserResponseSerializer
  //注意:如果返回的數(shù)據(jù)既不是xml也不是json那么應(yīng)該修改解析方案為:
  //manager.responseSerializer = [AFXMLParserResponseSerializer serializer];
  manager.responseSerializer = [AFHTTPResponseSerializer serializer];
  
  //2.發(fā)送GET請求
  [manager GET:@"http://120.25.226.186:32812/resources/images/minion_01.png" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task,id  _Nullable responseObject) {
      NSLog(@"網(wǎng)絡(luò)請求2");
      
      //UIImage *image = [UIImage imageWithData:responseObject];
  } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
      
  }];

    }

開發(fā)需求02：兩個網(wǎng)絡(luò)請求后刷新界面

  • (void)viewDidLoad {
    [super viewDidLoad];
    // 創(chuàng)建信號量
    semaphore = dispatch_semaphore_create(0);
    // 創(chuàng)建全局并行
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, queue, ^{
    // 請求一
    [self request1];
    NSLog(@"1");
    });
    dispatch_group_async(group, queue, ^{

      NSLog(@"2");

  // 請求二
  [self request2];

    });

    dispatch_group_notify(group, queue, ^{
    // 2個請求對應(yīng)2次信號等待
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    NSLog(@"刷新界面");
    });
    }

  • (void)request1{

    //1.創(chuàng)建會話管理者
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

    //注意:如果返回的是xml數(shù)據(jù),那么應(yīng)該修改AFN的解析方案AFXMLParserResponseSerializer
    //注意:如果返回的數(shù)據(jù)既不是xml也不是json那么應(yīng)該修改解析方案為:
    //manager.responseSerializer = [AFXMLParserResponseSerializer serializer];

    //告訴AFN能夠接受text/html類型的數(shù)據(jù)
    manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/html"];

    manager.responseSerializer = [AFHTTPResponseSerializer serializer];

    //2.發(fā)送GET請求
    [manager GET:@"http://www.baidu.com" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task,id _Nullable responseObject) {

         //02發(fā)送信號量計數(shù)+1
     dispatch_semaphore_signal(semaphore);
    NSLog(@"網(wǎng)絡(luò)請求1");
  //UIImage *image = [UIImage imageWithData:responseObject];
  NSLog(@"block-%@",[NSThread currentThread]);

    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
    dispatch_semaphore_signal(semaphore);
    NSLog(@"請求失敗--%@",error);
    }];

}

  • (void)request2{

      //1.創(chuàng)建會話管理者
  AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
  
  //注意:如果返回的是xml數(shù)據(jù),那么應(yīng)該修改AFN的解析方案AFXMLParserResponseSerializer
  //注意:如果返回的數(shù)據(jù)既不是xml也不是json那么應(yīng)該修改解析方案為:
  //manager.responseSerializer = [AFXMLParserResponseSerializer serializer];
  manager.responseSerializer = [AFHTTPResponseSerializer serializer];
  
  //2.發(fā)送GET請求
  [manager GET:@"http://120.25.226.186:32812/resources/images/minion_01.png" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task,id  _Nullable responseObject) {
      NSLog(@"網(wǎng)絡(luò)請求2");
      dispatch_semaphore_signal(semaphore);

      //UIImage *image = [UIImage imageWithData:responseObject];
  } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
      dispatch_semaphore_signal(semaphore);

  }];

    }

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