GCD中的dispatch_apply的用法及功用

 1 /*! 2  *  @brief  dispatch_apply的用法 3  */ 4 - (void)dispatchApplyTest1 { 5     //生成全局队列 6     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); 7      8      9     /*! dispatch_apply函数说明10      *11      *  @brief  dispatch_apply函数是dispatch_sync函数和Dispatch Group的关联API12      *         该函数按指定的次数将指定的Block追加到指定的Dispatch Queue中,并等到全部的处理执行结束13      *14      *  @param 10    指定重复次数  指定10次15      *  @param queue 追加对象的Dispatch Queue16      *  @param index 带有参数的Block, index的作用是为了按执行的顺序区分各个Block17      *18      */19     dispatch_apply(10, queue, ^(size_t index) {20         NSLog(@"%zu", index);21     });22     NSLog(@"done");23     24     /*!25      *  @brief  输出结果26      *27      2016-02-25 19:24:39.102 dispatch_apply测试[2985:165004] 028      2016-02-25 19:24:39.102 dispatch_apply测试[2985:165086] 129      2016-02-25 19:24:39.104 dispatch_apply测试[2985:165004] 430      2016-02-25 19:24:39.104 dispatch_apply测试[2985:165004] 531      2016-02-25 19:24:39.104 dispatch_apply测试[2985:165004] 632      2016-02-25 19:24:39.103 dispatch_apply测试[2985:165088] 333      2016-02-25 19:24:39.104 dispatch_apply测试[2985:165004] 734      2016-02-25 19:24:39.105 dispatch_apply测试[2985:165004] 835      2016-02-25 19:24:39.105 dispatch_apply测试[2985:165004] 936      2016-02-25 19:24:39.102 dispatch_apply测试[2985:165087] 237      2016-02-25 19:24:39.105 dispatch_apply测试[2985:165004] done38      *  !!!因为在Global Dispatch Queue中执行,所以各个处理的执行时间不定39      但done一定会输出在最后的位置,因为dispatch_apply函数会等待所以的处理结束40      */41 }

 1 /*! 2  *  @brief  实例:当要对NSArray类对象的所有元素执行处理时,不必一个一个的编写for循环部分 3  */ 4 - (void)dispatchApplyTest2 { 5     //1.创建NSArray类对象 6     NSArray *array = @[@"a", @"b", @"c", @"d", @"e", @"f", @"g", @"h", @"i", @"j"]; 7      8     //2.创建一个全局队列 9     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);10     11     //3.通过dispatch_apply函数对NSArray中的全部元素进行处理,并等待处理完成,12     dispatch_apply([array count], queue, ^(size_t index) {13         NSLog(@"%zu: %@", index, [array objectAtIndex:index]);14     });15     NSLog(@"done");16     /*!17      *  @brief  输出结果18      *19      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167871] 0: a20      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167956] 1: b21      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167957] 3: d22      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167871] 4: e23      2016-02-25 19:37:17.309 dispatch_apply测试[3010:167957] 6: g24      2016-02-25 19:37:17.309 dispatch_apply测试[3010:167871] 7: h25      2016-02-25 19:37:17.309 dispatch_apply测试[3010:167957] 8: i26      2016-02-25 19:37:17.309 dispatch_apply测试[3010:167871] 9: j27      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167956] 5: f28      2016-02-25 19:37:17.308 dispatch_apply测试[3010:167955] 2: c29      *  !!!因为在Global Dispatch Queue中执行,所以各个处理的执行时间不定30         但done一定会输出在最后的位置,因为dispatch_apply函数会等待所以的处理结束31      */32 }

 1 /*! 2  *  @brief  推荐在dispatch_async函数中异步执行dispatch_apply函数 3     效果     dispatch_apply函数与dispatch_sync函数形同,会等待处理执行结束 4  */ 5 - (void)dispatchApplyTest3 { 6     NSArray *array = @[@"a", @"b", @"c", @"d", @"e", @"f", @"g", @"h", @"i", @"j"]; 7     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); 8      9     dispatch_async(queue, ^{10         11         dispatch_apply([array count], queue, ^(size_t index) {12             NSLog(@"%zu: %@", index, [array objectAtIndex:index]);13         });14         15         dispatch_async(dispatch_get_main_queue(), ^{16             NSLog(@"回到主线程执行用户界面更新等操作");17         });18         19     });20     /*!21      *  @brief  执行结果22      *23      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171856] 3: d24      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171852] 1: b25      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171853] 2: c26      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171850] 0: a27      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171856] 4: e28      2016-02-25 19:49:53.189 dispatch_apply测试[3060:171852] 5: f29      2016-02-25 19:49:53.190 dispatch_apply测试[3060:171853] 6: g30      2016-02-25 19:49:53.190 dispatch_apply测试[3060:171850] 7: h31      2016-02-25 19:49:53.190 dispatch_apply测试[3060:171852] 9: j32      2016-02-25 19:49:53.190 dispatch_apply测试[3060:171856] 8: i33      2016-02-25 19:49:53.218 dispatch_apply测试[3060:171760] 回到主线程执行用户界面更新等操作34      *35      */36 }