Question

I’m having trouble saving to one variable letsMeet.startTimeLabel. Right after selecting NSLog shows the correct Value, however, after I save to another variable (letsMeet.endTimeLabel), letsMeet.startTimeLabel changes to (NULL). Below is the code:

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
switch (actionSheet.tag)
{
    case 1:
    {
        if (buttonIndex == 0)
        {
            UIDatePicker *startDatePicker = (UIDatePicker *)[actionSheet viewWithTag:kDatePickerTag1];

            NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
            [dateFormatter setDateFormat:@"dd"];
            NSDate *selectedDate = [startDatePicker date];

            NSDateFormatter *dayFormatter = [[NSDateFormatter alloc] init];
            [dayFormatter setDateFormat:@"EEEE"];
            NSDate *selectedDay= [startDatePicker date];

            NSDateFormatter *monthFormatter = [[NSDateFormatter alloc] init];
            [monthFormatter setDateFormat:@"MMMM"];
            NSDate *selectedMonth = [startDatePicker date];

            NSString *date = [[NSString alloc] initWithFormat:@"%@", [dateFormatter stringFromDate:selectedDate]];
            DateLabel.text = date;
            [letsMeet setDateLabel:date];

            NSString *month = [[NSString alloc] initWithFormat:@"%@", [dayFormatter stringFromDate:selectedMonth]];
            MonthLabel.text = month;
            [letsMeet setMonthLabel:month];

            NSString *day = [[NSString alloc] initWithFormat:@"%@", [monthFormatter stringFromDate:selectedDay]];
            DayLabel.text = day;
            [letsMeet setDateLabel:day];

            NSDateFormatter *timeFormatter = [[NSDateFormatter alloc] init];
            [timeFormatter setDateFormat: @"h:mm a"];
            NSDate *selectedStartTime = [startDatePicker date];

            NSString *startTime = [[NSString alloc] initWithFormat:@"%@", [timeFormatter stringFromDate:selectedStartTime]];
            StartTimeLabel.text = startTime;
            [letsMeet setStartTimeLabel:startTime];

            NSError *error = nil;
            if (![managedObjectContext save:&error]){

                NSLog(@"Error Saving");
            }
        }
        NSLog (@"This is the StartTime after selecting %@", letsMeet.startTimeLabel);
    }
    break;

    case 2:
    {
        if (buttonIndex == 0)
        {
            UIDatePicker *endTimePicker = (UIDatePicker *)[actionSheet viewWithTag:kDatePickerTag2];
            NSDateFormatter *endTimeFormatter = [[NSDateFormatter alloc] init];
            [endTimeFormatter setDateFormat: @"h:mm a"];
            NSDate *endSelectedTime = [endTimePicker date];
            NSString *endTime = [[NSString alloc] initWithFormat:@"%@", [endTimeFormatter stringFromDate:endSelectedTime]];
            EndTimeLabel.text = endTime;
            [letsMeet setEndTimeLabel:endTime];
            NSLog (@"This is the EndTime %@", letsMeet.endTimeLabel);
            NSLog (@"This is the StartTime after selecting BOTH %@", letsMeet.startTimeLabel);
        }
        else if (buttonIndex == 1)
        {
            EndTimeLabel.text = @"Whenever";
            [letsMeet setEndTimeLabel:EndTimeLabel.text];
        }
        NSError *error = nil;
        if (![managedObjectContext save:&error]) {
    }

}break;

    // Handle the error.
}

}


-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    UIViewController *destinationViewController = segue.destinationViewController;
    NSLog (@"Prepare For Segue StartTime %@", letsMeet.startTimeLabel);
    NSLog (@"Prepare For Segue EndTime%@", letsMeet.endTimeLabel);
}

Here is the log:

2013-02-20 21:38:24.253 AppointmentTime[3129:c07] This is the StartTime after selecting 9:30 AM
2013-02-20 21:38:32.325 AppointmentTime[3129:c07] This is the EndTime 12:15 PM
2013-02-20 21:38:32.325 AppointmentTime[3129:c07] This is the StartTime after Selecting BOTH (null)
2013-02-20 21:38:34.069 AppointmentTime[3129:c07] Prepare For Segue StartTime (null)
2013-02-20 21:38:34.069 AppointmentTime[3129:c07] Prepare For Segue EndTime12:15 PM

Q: Why would letsMeet.startTimeLabel show up correct the first time and after selecting EndTime, it changes to NULL. Please note EndTime continues to show the correct Value all the way up to prepareForSegue. Weird!

Answer 1

According to your logs and code , you are entering the switch block twice. Which means you are entering the actionSheet:clickedButtonAtIndex: method twice. So each time you enter the method

letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];

statement is executed twice, in turn creating two objects. You can see this by doing a fetch from the store.

So you are checking for properties in two different objects and hence the null.

If you are using just one managed object, you can probably add a check for nil for the object before executing insertNewObjectForEntityForName:inManagedObjectContext:. This will make sure you are using the same object.

If you are using more than one object at the same time use the object id or some unique key to identify your object and manipulate it.

Edit:
You can check for nil with the following code:

if(letsMeet==Nil){
    letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
}

This will work only, if the object you are calling the actionSheet:clickedButtonAtIndex: method is always in memory. But since you are persisting you might want to fetch the object from the store and then check for no. of objects.

NSError *error;
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext]];
NSArray *objectArray = [managedObjectContext executeFetchRequest:request error:&error]
if(objectArray.count==0){
    letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
}else{
    letsMeet = (LetsMeet *)[objectArray objectAtIndex:0];
}

Note: If you need to persist only a couple of variables, core-data might be an overkill. Use NSUserDefaults instead and keep it simple.