倒数计时器：更新控制器视图标签

Question

我正在尝试设置倒数计时器。我有两个视图控制器：ViewController 和 EditViewController。 ViewController 有两个标签小时和分钟。 EditViewController 有一个 UIDatePicker 和一个保存按钮。当用户在 UIDatePicker 上选择时间并点击保存时，它们将被重定向回 ViewController，并且小时和分钟标签会填充所选时间和当前时间之间的差异。这会自动更新，直到差异为 0。我在尝试让小时和分钟正确显示在 ViewController 标签上时遇到问题。这是我的代码：

ViewController.m

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.hourLabel.text = self.hourText;
    self.minuteLabel.text = self.minuteText;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

EditViewController.h

@interface EditViewController : UIViewController
@property (weak, nonatomic) IBOutlet UIDatePicker *datePicker;
@property (weak, nonatomic) IBOutlet NSString *currentTimeString;
@property (weak, nonatomic) IBOutlet NSString *endTimeString;
- (IBAction)saveButton:(id)sender;
- (IBAction)cancelButton:(id)sender;

-(void)updateTime;

@end

EditViewController.m

#import "EditViewController.h"
#import "ViewController.h"

@interface EditViewController ()

@end

@implementation EditViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self)
    {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)saveButton:(id)sender
{

    NSCalendar *now = [NSCalendar autoupdatingCurrentCalendar];
    NSInteger currentTime = (NSHourCalendarUnit | NSSecondCalendarUnit);
    self.datePicker.date = [now dateFromComponents:[now components:currentTime fromDate:self.datePicker.date]];

    NSTimer *timer;
    timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateTime) userInfo:nil repeats:YES];

    [self dismissViewControllerAnimated:YES completion:nil];
}

-(void)updateTime
{
    NSInteger timeLeft = ((NSInteger)[self.datePicker.date timeIntervalSinceNow]);
    NSInteger minutes = (timeLeft / 60) % 60;
    NSInteger hours = (timeLeft / 3600) % 24;

    ViewController *controller;
    controller.hourText = [NSString stringWithFormat:@"%ldi",(long)hours];
    controller.minuteText = [NSString stringWithFormat:@"%ldi",(long)minutes];
    NSLog(@"The time is %ld",(long)timeLeft);

}

- (IBAction)cancelButton:(id)sender
{
    [self dismissViewControllerAnimated:YES completion:nil];
}

@end

感谢任何帮助。提前致谢。

Answer 1

在此处查看您的代码中已编辑的方法。这将完全满足您的要求。

#import "EditViewController.h"
#import "ViewController.h"
#import "AppDelegate.h"
@interface EditViewController ()
{
    AppDelegate *appDelegate;
}
@end

@implementation EditViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self)
    {
        // Custom initialization
        appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    }
    return self;
}


-(void)updateTime
{
    NSInteger timeLeft = ((NSInteger)[self.datePicker.date timeIntervalSinceNow]);
    NSInteger minutes = (timeLeft / 60) % 60;
    NSInteger hours = (timeLeft / 3600) % 24;

    NSString *hourText = [NSString stringWithFormat:@"%ldi",(long)hours];
    NSString *minuteText = [NSString stringWithFormat:@"%ldi",(long)minutes];

    [appDelegate updateTime:hourText andMinute:minuteText];

}

最后，在 AppDelegate 类中定义一个方法

- (void) updateTime:(NSString *)hourStr andMinute:(NSString *)minuteStr
{
   for(id obj in [self.navigationController viewControllers])
   {
      if([obj isKindOfClass:ViewController])
      {
        ViewController *vcObj = (ViewController *)obj;
        vcObj.hourLabel.text = hourStr;
        vcObj.minuteLabel.text = minuteStr;

      }
   }
}

Answer 2

几个问题：

ViewController.m

self.hourLabel.text = self.hourText;
self.minuteLabel.text = self.minuteText;

应该在viewWillAppear 而不是viewDidLoad。发生的事情是您在应用加载时设置文本。 viewDidLoad 只会为该应用程序实例触发一次。当您从 EditViewController 回来时，您需要做的是更新它，对吗？所以如果你把它放在viewWillAppear，当你回来时它也会被调用并为你更新。

接下来的事情：

EditViewController.m

ViewController *controller;
controller.hourText = [NSString stringWithFormat:@"%ldi",(long)hours];
controller.minuteText = [NSString stringWithFormat:@"%ldi",(long)minutes];
NSLog(@"The time is %ld",(long)timeLeft);

这段代码 sn-p 声明了一个新的 ViewController 变量（嗯，大部分情况下，您都缺少= [ViewController new] 部分）。这样做的问题是您对这个控制器没有做任何事情。 ViewController 实际上已经在您的导航堆栈中（我假设 NavigationController，因为您在用户返回时说过），因此您需要使用对 ViewController 的引用，您的应用程序已经实例化，而不是创建一个新的，因为您从未使用过这个人任何地方。