IOS converting hours to seconds from a NSString [duplicate] - ios

Question

This question already has answers here:
Can't convert from NSString to NSDate
(2 answers)
Closed 9 years ago.
I'm trying to convert a NSString into seconds, but i'm doing something wrong. This is my code:
The text in _myTextField, come from a uidatepicker in the format of HH:mm.
NSString *teste = [[NSString alloc]init];
teste = [_myTextField text];
NSDateFormatter *formatarteste = [[NSDateFormatter alloc]init];
[formatarteste setDateFormat:#"s"];
NSDate *dateFromString = [[NSDate alloc]init];
dateFromString = [formatarteste dateFromString:teste];
NSLog(#"%#", dateFromString);
i Always get i null result on the nslog. I tried to convert the dateFromString, back to a string before using NSLog, but still got a null message.
As requested here is more of the code i using:
I have a textfield that calls a uidatepicker, that is load on super viewdidload:
[_myTextField setText:#"03:00"];
UIDatePicker *datepicker = [[UIDatePicker alloc]init];
//[datepicker setDate:[NSDate date]];
[datepicker setDatePickerMode:UIDatePickerModeTime];
[datepicker addTarget:self action:#selector(updateTextField:) forControlEvents:UIControlEventValueChanged];
[self.myTextField setInputView:datepicker];
And this is the updateTextfield function:
UIDatePicker *picker = (UIDatePicker*)self.myTextField.inputView;
NSDateFormatter *formatar = [[NSDateFormatter alloc]init];
[formatar setDateFormat:#"HH:mm"];
NSString *textoDoField = [formatar stringFromDate:picker.date];
self.myTextField.text = [NSString stringWithFormat:#"%#", textoDoField];

Answer 1

One way (not necessarily the simplest) to calculate seconds since midnight from the time;
// NSString *teste = #"14:52";
NSDateFormatter *formatarteste = [[NSDateFormatter alloc]init];
[formatarteste setTimeZone:[NSTimeZone timeZoneWithName:#"UTC"]];
[formatarteste setDateFormat:#"HH:mm"];
NSDate *dateFromString = [formatarteste dateFromString:teste];
NSTimeInterval interval =
[dateFromString timeIntervalSinceDate:
[NSDate dateWithString: #"2000-01-01 00:00:00 +0000"]];
NSLog(#"%f", interval);
// >>> 53520
...or the somewhat more straight forward;
// NSString *teste = #"14:52";
int h,m;
const char *bytes = [teste UTF8String];
sscanf(bytes, "%d:%d", &h,&m);
int seconds = h*3600+m*60;
NSLog(#"%d", seconds);
// >>> 53520

Answer 2

Guys i was looking at this at wrong way, i did not need to transform the NSString into a NSDate.
I just need to get the NSString like 03:00, separate the "hours" from the "minutes", then, i multiple the hours x 3600 and the minutes x 60, to get the seconds in 3 hours for example.
The whole point of this was to create a Notification that run in a determinate time, using the [NSDate dateWithTimeIntervalSinceNow: NUMBER OF SECONDS FOR THE NOTIFICATION APPEAR];
And thats it!
This is the code i using to get the Seconds, from the textfield string:
NSArray *arrayWithNumberValue = [teste componentsSeparatedByCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:#":"]];
NSInteger valorHoras = [arrayWithNumberValue[0] intValue];
NSInteger valorMin = [arrayWithNumberValue[1] intValue];
NSInteger horasEmSegundos = valorHoras * 3600;
NSInteger minEmSegundos = valorMin * 60;
NSInteger proximoAlarme = horasEmSegundos + minEmSegundos;
manualTimer *horamanual = [[manualTimer alloc]init];
[horamanual tempoAlerta:&proximoAlarme];
NSLog(#"%ld", (long)proximoAlarme);