Creating a StopWatch in Iphone

问题:

I am trying to create a simple stopwatch. I referred to this website ( http://www.apptite.be/tutorial_ios_stopwatch.php) to do this app. When I click the start button, I get -596:-31:-23:-648 and the stopwatch does not run.

The code looks like:

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController{
    UILabel *lbl;
    NSTimer *stopTimer;
    NSDate *startDate;
}

@property (strong,nonatomic) IBOutlet UILabel *lbl;

-(IBAction)startPressed:(id)sender;
-(IBAction)stopPressed:(id)sender;

-(void)updateTimer;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize lbl;

- (void)viewDidLoad
{
    [super viewDidLoad];
    lbl.text = @"00.00.00.000";
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)startPressed:(id)sender{
    if (stopTimer == nil) {
        stopTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
                                                     target:self
                                                   selector:@selector(updateTimer)
                                                   userInfo:nil
                                                    repeats:YES];
    }
}
-(IBAction)stopPressed:(id)sender{
    [stopTimer invalidate];
    stopTimer = nil;
    //[self updateTimer];

}
-(void)updateTimer{
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"HH:mm:ss.SSS"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString=[dateFormatter stringFromDate:timerDate];
    lbl.text = timeString;
}

@end

Need some guidance on solving the error. Not sure where the error is. Appreciate any help...

回答1:

Solved the errors:

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController{
    UILabel *lbl;
    NSTimer *stopTimer;
    NSDate *startDate;
    BOOL running;
}

@property (strong,nonatomic) IBOutlet UILabel *lbl;

-(IBAction)startPressed:(id)sender;
-(IBAction)resetPressed:(id)sender;

-(void)updateTimer;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize lbl;

- (void)viewDidLoad
{
    [super viewDidLoad];
    lbl.text = @"00.00.00.000";
    running = FALSE;
    startDate = [NSDate date];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(IBAction)startPressed:(id)sender{
    if(!running){
        running = TRUE;
        [sender setTitle:@"Stop" forState:UIControlStateNormal];
        if (stopTimer == nil) {
            stopTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
                                                         target:self
                                                       selector:@selector(updateTimer)
                                                       userInfo:nil
                                                        repeats:YES];
        }
    }else{
        running = FALSE;
        [sender setTitle:@"Start" forState:UIControlStateNormal];
        [stopTimer invalidate];
        stopTimer = nil;
    }

}
-(void)updateTimer{
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"HH:mm:ss.SSS"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString=[dateFormatter stringFromDate:timerDate];
    lbl.text = timeString;
}

-(IBAction)resetPressed:(id)sender{
    [stopTimer invalidate];
    stopTimer = nil;
    startDate = [NSDate date];
    lbl.text = @"00.00.00.000";
    running = FALSE;
}

@end

Slight alterations to the code have been made.. But it is working correctly now...

回答2:

I created a simple stopwatch with pause/resume capability. It uses two NSDate variables to keep track of time between pausing:

NSTimeInterval secondsBetween = [pause_date timeIntervalSinceDate:start_date];
start_date = [NSDate dateWithTimeIntervalSinceNow:(-1)*secondsBetween];

Check out the example project here: https://github.com/kevinpk/NSStopwatch