返回UIViewController时UILabel不更新
我有一个简单的应用程序，在appDelegate中有一个NSTimer对象供所有视图访问。 应用程序的结构是使用UINavigationController。 当我触发NSTimer对象时，我的UILabel正在使用正确的倒计时function进行更新，但是当我返回到rootViewController并返回到倒数计时器视图时，我的UILabel正在使用当前的倒计时时间进行更新，但没有后续更新UILabel发生了。 我错过了什么？ 我已经做过研究确保UILabel对象不是nil，我在viewDidAppear方法上调用该函数，似乎没有任何工作！ 这是代码：
AppDelegate.h
@interface AppDelegate : UIResponder { } @property (nonatomic, retain) NSTimer *countdownTimer; AppDelegate.m
@implementation AppDelegate @synthesize countdownTimer;
CountdownTimerViewController.h
#import "AppDelegate.h" enter code here @interface CountdownTimerViewController : UIViewController { enter code here AppDelegate *appdelegate; } @property (strong, nonatomic) IBOutlet UILabel *labelCountdownTimer; @property (strong, nonatomic) IBOutlet UIButton *buttonStartTimer; @property (strong, nonatomic) IBOutlet UIButton *buttonStopTimer; - (IBAction)startTimer:(id)sender; - (IBAction)stopTimer:(id)sender;
CountdownTimerViewController.m
@implementation CountdownTimerViewController @synthesize labelCountdownTimer; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. //Instatiating Appdelegate if(!appdelegate) appdelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate]; } - (void) viewDidAppear:(BOOL)animated { if ([appdelegate.countdownTimer isValid]) { [self countDown]; } } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } #pragma mark - Button Action Methods - (IBAction)startTimer:(id)sender { [self updateCounter]; } - (IBAction)stopTimer:(id)sender { [appdelegate.countdownTimer invalidate]; labelCountdownTimer.text = @"00:00:00"; } int countLimit=30; //seconds NSDate *startDate; - (void)countDown { if([[NSDate date] timeIntervalSinceDate:startDate] >= countLimit) { [appdelegate.countdownTimer invalidate]; return; } else { NSDate *currentDate = [NSDate date]; NSTimeInterval timeInterval = -([currentDate timeIntervalSinceDate:startDate]); NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval]; NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateFormat:@"mm:ss"]; [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]]; NSString *timeString = [dateFormatter stringFromDate:timerDate]; NSLog(@"timeString: %@",timeString); NSLog(@"labelCountdownTimer: %@",labelCountdownTimer); labelCountdownTimer.text = timeString; } } - (void)updateCounter { labelCountdownTimer.text = @"00:00:00"; startDate = [NSDate date]; appdelegate.countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0 target:self selector:@selector(countDown) userInfo:nil repeats:YES]; }
感谢大家的意见。 我实际上通过执行一个方法来解决它，它将检索NSTimer在我的AppDelegate中更新的值，因为当我离开视图并返回它时，触发NSTimer的方法不再在主线程中。 只要我的NSTimer有效，此方法就会循环。 我还放置了一个延迟，允许UI更新值，然后再次执行该方法。 以下是代码，以防有人遇到类似的问题。 我从chandan提供的建议中得到了这个想法，谢谢！
AppDelegate.h
@interface AppDelegate : UIResponder { } @property (nonatomic, retain) NSTimer *countdownTimer; @property (nonatomic, retain) NSString *timeString;
AppDelegate.m
@interface AppDelegate : UIResponder { } @property (nonatomic, retain) NSTimer *countdownTimer; @property (nonatomic, retain) NSString *timeString;
CountdownTimerViewController.h
@interface CountdownTimerViewController : UIViewController { AppDelegate *appdelegate; } @property (strong, nonatomic) IBOutlet UILabel *labelCountdownTimer; @property (strong, nonatomic) IBOutlet UIButton *buttonStartTimer; @property (strong, nonatomic) IBOutlet UIButton *buttonStopTimer; - (IBAction)startTimer:(id)sender; - (IBAction)stopTimer:(id)sender;
CountdownTimerViewController.m
@implementation CountdownTimerViewController @synthesize labelCountdownTimer; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. //Instatiating Appdelegate if(!appdelegate) appdelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate]; } - (void) viewDidAppear:(BOOL)animated { if ([appdelegate.countdownTimer isValid]) { [self updateLabel]; } else { labelCountdownTimer.text = @"00:00:00"; } } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } #pragma mark - Button Action Methods - (IBAction)startTimer:(id)sender { [self updateCounter]; } - (IBAction)stopTimer:(id)sender { [appdelegate.countdownTimer invalidate]; labelCountdownTimer.text = @"00:00:00"; } int countLimit=30; //seconds NSDate *startDate; - (void)updateCounter { labelCountdownTimer.text = @"00:00:00"; startDate = [NSDate date]; appdelegate.countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0 target:self selector:@selector(countDown) userInfo:nil repeats:YES]; } - (void)countDown { if([[NSDate date] timeIntervalSinceDate:startDate] >= countLimit) { [appdelegate.countdownTimer invalidate]; return; } else { NSDate *currentDate = [NSDate date]; NSTimeInterval timeInterval = -([currentDate timeIntervalSinceDate:startDate]); NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval]; NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateFormat:@"mm:ss"]; [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]]; appdelegate.timeString = [dateFormatter stringFromDate:timerDate]; labelCountdownTimer.text = appdelegate.timeString; } } - (void) updateLabel { if ([appdelegate.countdownTimer isValid]) { labelCountdownTimer.text = appdelegate.timeString; [self performSelector:@selector(updateLabel) withObject:nil afterDelay:0.05]; } }
像这样输入：
appdelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
实际上不会将UIApplicationDelegate放入AppDelegate类并添加额外的参数。 因此，此变量中没有指向计时器的指针。
您需要一种不同的方法来存储计时器指针。
尝试在主线程上更新UILabel上的文本。 有时UILabel中的更新不适用于backgound线程。
- (void) viewDidAppear:(BOOL)animated { if ([appdelegate.countdownTimer isValid]) { [self performSelectorOnMainThread:@selector(countDown) withObject:nil waitUntilDone:NO]; } }
如果您的appdelegate对象工作正常并且正在使用当前倒计时时间更新UILabel，但是没有对UILabel进行后续更新，那么在主线程上应用UI更改就像它一样
- (void)countDown { [self performSelectorOnMainThread:@selector(changeCountDownValue) withObject:nil waitUntilDone:NO]; } - (void)changeCountDownValue { if([[NSDate date] timeIntervalSinceDate:startDate] >= countLimit) { [appdelegate.countdownTimer invalidate]; return; } else { NSDate *currentDate = [NSDate date]; NSTimeInterval timeInterval = -([currentDate timeIntervalSinceDate:startDate]); NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval]; NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateFormat:@"mm:ss"]; [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]]; NSString *timeString = [dateFormatter stringFromDate:timerDate]; NSLog(@"timeString: %@",timeString); NSLog(@"labelCountdownTimer: %@",labelCountdownTimer); labelCountdownTimer.text = timeString; } }
请仔细检查NSTimer对象。 它应该适用于UILabel更新。 如果仍有问题，请告诉我。