今天博主有一個倒計時效果的實現的需求,遇到了一些困難點,在此和大家分享,希望能夠共同進步.

首先在需要用到的地方解析總的倒計時時間,博主沒有封裝,各位看官可以自行封裝

#PRagma mark--------新修改,增加倒計時

                NSString *stringOfTime=[NSString stringWithFormat:@"%@",d[@"sh

                double endUnixTime = [stringOfTime doubleValue];

//                NSLog(@"++++++%.2f",endUnixTime);

                NSCalendar *cal = [NSCalendar currentCalendar];

                unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;

                NSDate *date1 = [NSDate date];

                NSDate *date2 = [NSDate dateWithTimeIntervalSince1970:endUnixTime];

                NSDateComponents *dOfd = [cal components:unitFlags fromDate:date1 toDate:date2 options:0];

                NSInteger sec = [dOfd hour]*3600+[dOfd minute]*60+[dOfd second];

                //sec是總秒數

//                NSLog(@"**********%@",dOfd);

                UILabel *labelOfTime=(UILabel *)[_scroll viewWithTag:6954321];

                if (sec>0) {

                    [self setCountDownWithTotalSec:sec withLabel:labelOfTime];

                }

 然后使用GCD實現倒計時功能

- (void)setCountDownWithTotalSec:(NSInteger)totalSec withLabel:(UILabel *)timeLbl{

    __block NSInteger timeout = totalSec; //倒計時時間

    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); //每秒執行

    dispatch_source_set_event_handler(_timer, ^{

        if(timeout<=0){ //倒計時結束，關閉

            dispatch_source_cancel(_timer);

            dispatch_async(dispatch_get_main_queue(), ^{

                //設置界面的按鈕顯示 根據自己需求設置

                timeLbl.text = @"00:00:00";

            });

        }else{

            long hours = timeout / 3600;

            long minutes = (timeout - hours * 3600) / 60;

            int seconds = timeout % 60;

            NSString *strTime = [NSString stringWithFormat:@"%.2ld%.2ld%.2d",hours,minutes, seconds];

            NSString *firstH = [strTime substringWithRange:NSMakeRange(0, 1)];

            NSString *secondH = [strTime substringWithRange:NSMakeRange(1, 1)];

            NSString *firstM = [strTime substringWithRange:NSMakeRange(2, 1)];

            NSString *secondM = [strTime substringWithRange:NSMakeRange(3, 1)];

            NSString *firstS = [strTime substringWithRange:NSMakeRange(4, 1)];

            NSString *secondS = [strTime substringWithRange:NSMakeRange(5, 1)];

            NSString *newTimeString = [NSString stringWithFormat:@"%@%@:%@%@:%@%@",firstH,secondH,firstM,secondM,firstS,secondS];

            dispatch_async(dispatch_get_main_queue(), ^{

                timeLbl.text = newTimeString;//回到主線程顯示

            });

            timeout--;

        }

    });

    dispatch_resume(_timer);

}

 上述定時方法在后臺無法運行,如果你的需求跟博主遇到的一樣BT,需要實時更新定時器,可以在回調中判斷程序狀態,取消定時,再監聽程序喚醒,重新創建定時器

    dispatch_source_set_event_handler(_timer, ^{

         if ([UIapplication sharedApplication].applicationState==UIApplicationStateBackground) {

            dispatch_source_cancel(_timer);

            dispatch_async(dispatch_get_main_queue(), ^{

                 //設置界面的按鈕顯示 根據自己需求設置

                timeLbl.text = @" ";

             });

        }