088实现自动倒计时功能

效果如下：

ViewController.h

1 #import <UIKit/UIKit.h>

2 

3 @interface ViewController : UIViewController

4 @property (strong, nonatomic) UIDatePicker *datePChoice;

5 @property (strong, nonatomic) NSTimer *timer;

6 

7 @end

ViewController.m

 1 #import "ViewController.h"

 2 

 3 @interface ViewController ()

 4 - (void)layoutUI;

 5 - (void)timerDidRun:(NSTimer *)sender;

 6 @end

 7 

 8 @implementation ViewController

 9 #define timeInterval 60.0

10 

11 - (void)viewDidLoad {

12     [super viewDidLoad];

13     

14     [self layoutUI];

15 }

16 

17 - (void)didReceiveMemoryWarning {

18     [super didReceiveMemoryWarning];

19     // Dispose of any resources that can be recreated.

20 }

21 

22 - (void)viewWillDisappear:(BOOL)animated {

23     [super viewWillDisappear:animated];

24     //画面隐藏时，取消计数器

25     if ([_timer isValid]) {

26         [_timer invalidate];

27     }

28 }

29 

30 - (void)layoutUI {

31     _datePChoice = [[UIDatePicker alloc] initWithFrame:CGRectMake(0, 0, 0, 0)];

32     CGPoint newPoint = self.view.center;

33     _datePChoice.center = newPoint;

34     _datePChoice.datePickerMode = UIDatePickerModeCountDownTimer;

35     //设置时间显示为1小时5分钟；即65分钟 ＝ 65 * 60（s）

36     _datePChoice.countDownDuration = 65 * 60;

37     [self.view addSubview:_datePChoice];

38     

39     //使用计数器；设置每隔timeInterval（60秒）循环调用一次

40     _timer = [NSTimer timerWithTimeInterval:8

41                                      target:self

42                                    selector:@selector(timerDidRun:)

43                                    userInfo:nil

44                                     repeats:YES]; //这里为了测试；更改timerWithTimeInterval:timeInterval为timerWithTimeInterval:8，即每隔8秒循环调用一次

45     NSRunLoop *runLoop = [NSRunLoop currentRunLoop];

46     [runLoop addTimer:_timer forMode:NSDefaultRunLoopMode];

47 }

48 

49 - (void)timerDidRun:(NSTimer *)sender {

50     if (_datePChoice.countDownDuration > 0.0) {

51         _datePChoice.countDownDuration -= timeInterval;

52     } else {

53         //日期选择器时间倒计时为0时，取消计数器

54         if ([_timer isValid]) {

55             [_timer invalidate];

56         }

57     }

58 }

59 

60 @end