Question

I am new to iPhone Development, and am making a countdown project using navigation controller and storyboard. My application has two views. The first view only has one button. When this button is clicked, it goes to the second view. The second view has the countdown objects. My problem is that when the countdown is running in second view, if I go back to first view and then hit the button to go to the second view, the countdown is no longer running.

Here is the code:

view1.h

#import <UIKit/UIKit.h>
#import "view2.h"

@interface view1: UIViewController

-(IBAction)nextpage:(id)sender;

@end

view1.m

@implementation view1


-(IBAction)nextpage:(id)sender
{
    view2 *next=[self.storyboard instantiateViewControllerWithIdentifier:@"secondview"];
    [self.navigationController pushViewController:next animated:YES];
}

@end

view2.h

@interface view2 : UIViewController
{
    IBOutlet UILabel *lbl;
    IBOutlet UITextField *field;

    NSTimer *theTimer;
    NSDate *targetDate;
    NSCalendar *cal;
    NSDateComponents *components;
}

@property (nonatomic,retain) IBOutlet UILabel *lbl;
@property (nonatomic,retain) IBOutlet UITextField *field;
-(IBAction)back_first_view;
@end

view2.m

@implementation view2
@synthesize lbl,field;

- (void)viewDidLoad
{
    cal = [[NSCalendar currentCalendar] retain];
    components = [[NSDateComponents alloc] init];
}

- (IBAction)buttonPressed:(id)sender {

    if (theTimer != nil) {
        return;
    }

    NSString *input = field.text;
    NSArray *timeSplit = [input componentsSeparatedByString:@":"];
    NSUInteger hours =  [[timeSplit objectAtIndex:0] intValue];
    NSUInteger minutes =  [[timeSplit objectAtIndex:1] intValue];
    NSDate *now = [NSDate date];
    NSDateComponents *dateComponents = [cal components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:now];
    [dateComponents setHour:hours];
    [dateComponents setMinute:minutes];

    if (!targetDate) {
        targetDate = [[cal dateFromComponents:dateComponents] retain];
    }
    else {
        targetDate = nil;
        targetDate = [[cal dateFromComponents:dateComponents] retain];
    }

    if ([targetDate timeIntervalSinceNow] > 0) {
        theTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(tick) userInfo:nil repeats:YES];
        [self hideKeyboard];
    }
    else {
        targetDate = nil;
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Cannot countdown because time is before now" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
        [alert release];
    }
}

- (void)tick {
    if ([targetDate timeIntervalSinceNow] <= 0) {
        //Checks if the countdown completed

        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Countdown Completed" message:@"YAY! The countdown has complete" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
        [alert release];

        return;
    }
    components = [cal components:(NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit) fromDate:[NSDate date] toDate:targetDate options:0];

    NSInteger hours = [components hour];
    NSInteger minutes = [components minute];
    NSInteger seconds = [components second];

    NSString *output = [NSString stringWithFormat:@"%i Hours\n%i Minutes\n%i Seconds\n", hours, minutes, seconds];
    lbl.text = output;
}

- (void)hideKeyboard {
    if ([field isFirstResponder]) [field resignFirstResponder];
}

- (IBAction)back_first_view
{
    [self.navigationController popToRootViewControllerAnimated:YES];
}
 @end

Answer 1

Change this method to,

- (IBAction)nextpage:(id)sender
{
    [self.navigationController pushViewController:self.next animated:YES];
}

And add the first line to your viewDidLoad or any such methods,

- (void)viewDidLoad {
       [super viewDidLoad]; //Always keep super call as first call in a method
       self.next = [self.storyboard instantiateViewControllerWithIdentifier:@"secondview"];
    // Do any additional setup after loading the view.
}

And declare next in .h file @interface as,

@interface view1 : UIViewController
{

}
@property (nonatomic, strong) view2 *next;

Each and and every time when you are going to next page, you were creating a new view2, which you need to change.