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