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__block int timeout=59; //倒计时时间         dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);         dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);         dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行                  dispatch_source_set_event_handler(_timer, ^{             if(timeout<=0){ //倒计时结束，关闭                 dispatch_source_cancel(_timer);                 dispatch_async(dispatch_get_main_queue(), ^{                     //设置界面的按钮显示 根据自己需求设置                     [_sendCodeBtn setTitle:@"" forState:UIControlStateNormal];                     [_sendCodeBtn setBackgroundImage:[UIImage imageNamed:@"btn_send_code"] forState:UIControlStateNormal];                     [_sendCodeBtn setUserInteractionEnabled:YES];                 });             }else{                 //            int minutes = timeout / 60;                                  int seconds = timeout % 60;                                  NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];                 dispatch_async(dispatch_get_main_queue(), ^{                     //设置界面的按钮显示 根据自己需求设置                     //                    NSLog(@"____%@",strTime);                     [_sendCodeBtn setTitle:[NSString stringWithFormat:@"%@秒后重新获取",strTime] forState:UIControlStateNormal];                     [_sendCodeBtn setBackgroundImage:[UIImage imageNamed:@"btn_send_code_disabled"] forState:UIControlStateNormal];                     [_sendCodeBtn setUserInteractionEnabled:NO];                 });                 timeout--;                              }         });         dispatch_resume(_timer);     }

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