Question

I am trying to create an app that calculates the time difference and the amount is multiplied by an amount in money. It is targeted to calculate in R$ (brazilian real) the amount that someone will have to pay for using a service during the time calculated by the app.

Here´s is my code:

- (IBAction)encerrar:(id)sender {

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"HH:mm";
    NSString *temp = inicio.text;
    NSDate *then = [dateFormatter dateFromString:temp];
    NSDate *now = [NSDate date];
    NSTimeInterval timeInterval = [now timeIntervalSinceDate:then];
    NSString *ext = [dateFormatter stringFromDate:now];
    fim.text = ext;
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString = [dateFormatter stringFromDate:timerDate];
    duracao.text = timeString;

    double timeIntervalInHours = (timeInterval / 3600.0) * 5;        

    NSString *vTotal = [[NSString alloc] initWithFormat:@"R$ %.2f", fecha];
    NSLog(@"%.2f", timeIntervalInHours);
    vlrTotal.text = vTotal;
}

The fact is that when we click on Calculate button, and if the duracao (duration) is equal to 1h it gives me the correct amount which is R$ 5,00. But when the duration is equal to 30mins or other value different from exact 1h, it gives the wrong amount.

I.E.: 1h should be R$ 5,00; while 1:30h should be R$ 7,50, but shows me R$ 6,50.

So, anyone could help me on this???

Thanks in advance!!!

Answer 1

timeInterval is the amount of time in seconds, so if you want it in hours and fractions of an hour just do this:

double timeIntervalInHours = timeInterval / 3600.0;

and then multiple timeIntervalInHours times the price/hour to get the cost.

EDIT
Based on our chat, I would create a button with “iniciar” (start) as the title. When they press that button, I would store the current time and change the title to “encerrar” (stop). (I hope that my translations are correct, lol) Then the button action would look something like this:

// self.startTime is a NSDate.
- (IBAction)iniciar_encerrar:(UIButton *)sender {
    if ([sender.titleLabel.text isEqualToString:@"iniciar"]) {
        // We are starting the time
        if (self.startTime != nil) {
            return;
        }

        self.startTime = [NSDate date];
        [sender setTitle:@"encerrar" forState:UIControlStateNormal];
    } else {
        // We are stopping the time
        NSDate *currentTime = [NSDate date];
        NSTimeInterval elapsedTimeInSeconds = [currentTime timeIntervalSinceDate:self.startTime];
        double cost = elapsedTimeInSeconds / 3600.0 * 5.0;
        NSLog(@"%.2lf", cost);

        // reset the button
        self.startTime = nil;
        [sender setTitle:@"iniciar" forState:UIControlStateNormal];
    }
}

startTime is declared as follows:

In your .h file, along with the other declared properties, add:

@property (strong, nonatomic) NSDate *startTime;

In your .m file, add this at the top with the other ones:

@synthesize startTime;

In your viewDidUnload function (in your .m file) add this:

startTime = nil;

This just gives you a place to store the startTime date.