将核心数据属性从NSString更改为NSDate，并使用日期选择器使此功能正常工作

Question

I am working through my first app and need some advice on how to approach this next task and issue. The premise of the app is the user has a table view, clicks on a plus button in the navigation bar and is presented with text fields to insert information. Upon clicking on save, that gets saved to the core data and displayed in the table view.

The table view is sectioned. Right now, I have the "date" being represented as a NSString, just to get my app off the ground, but I need to change this to a DatePicker. The sections' are based on the Dates.

I have a Core Data Model as follows:

• Transaction Entity
• Person Entity
• Occasion Entity
• Date Entity

The Transaction Entity has a relationship to each of the other entities here.

As mentioned, at first, to get my app working and off the ground, I made the Date Entity have a dateOfEvent attribute which was a NSString rather than a NSDate but of course that will not work in the long run.

I have changed my model to NSDate for this attribute and regenerated the NSManagedObject Subclasses.

Independently, I have a DatePicker working without any issues but it outputs the information to a String in a textfield.

What I want to achieve now is to use the DatePicker, select a date and have that saved to the Core Data Date Entity (dateOfEvent attribute) which I can then use in the table view as the section titles.

Here is my code for saving in the view controller:

- (IBAction)save:(id)sender
{
    NSManagedObjectContext *context = [self managedObjectContext];
    Transaction *transaction = [NSEntityDescription insertNewObjectForEntityForName:@"Transaction" inManagedObjectContext:context];
    Date *enteredDate = (Date *)[Date occasionWithDate:self.dateTextField.text inManagedObjectContext:context];
    transaction.dates = enteredDate;
    // Code to save Person, Occasion, etc. 
}

The enteredDate is calling a specific occasionWithDate method:

+ (Date *)occasionWithDate:(NSString *)enteredDate inManagedObjectContext:(NSManagedObjectContext *)context
    Date *date = nil;
    // Creating a fetch request to check whether the name of the person already exists
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Date"];
    request.predicate = [NSPredicate predicateWithFormat:@"dateOfEvent = %@", enteredDate];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"dateOfEvent" ascending:YES];
    request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    NSError *error = nil;
    NSArray *dates = [context executeFetchRequest:request error:&error];
    if (!dates)
    {
        // Handle Error
    }
    else if (![dates count])
    {
        // If the person count is 0 then let's create it
        date = [NSEntityDescription insertNewObjectForEntityForName:@"Date" inManagedObjectContext:context];
        date.dateOfEvent = enteredDate;
    }
    else
    {
        // If the object exists, just return the last object .
        date = [dates lastObject];
    }
    return date;
}

This does a fetchRequest to ensure I am either returning an existing date or adding a new one if that does not exist.

That is the behaviour I would like here, but of course, that method is passing a String and I need to pass a date.

With this in mind, how do I go about selecting the value of the DatePicker, adding it to the Core Data database in the same way as above (checking whether the date exists) and having this displayed in the sections of the Table View?

The reason I want to check if the date exists is because if there is an event on the 2nd December 2013, it'll be unique. However if I create another event on the 2nd December 2013, I'd want it to use the existing 2nd December, rather than create a second entry for 2nd December. The reason is my app has a tab view where the second tab is predicated by dates and so I would not want two separate 2nd December there.

This is a side note. The main thing I would like to achieve is, use the Date Picker and save the selected value to Transaction.dates.dateOfEvent to Core Data.

I know if I were to do something like date.dateOfEvent = [NSDate date] ; it would be assigning the date and time now. That is not what I want here.

Any assistance would be massively appreciated.

Thanks,

EDIT: Adding in UIDatePicker Code - this first code snippet below is for saving to the textField when using NSString as the attribute

In viewDidLoad

    [self.datePicker addTarget:self action:@selector(getSelection:) forControlEvents:UIControlEventValueChanged];

-(void)getSelection:(id)sender
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateStyle:NSDateFormatterLongStyle];
    [dateFormatter setTimeStyle:NSDateFormatterNoStyle];

    NSDate *date = [self.datePicker date];

    NSString *formattedDateString = [dateFormatter stringFromDate:date];
    self.dateTextField.text = formattedDateString;
}

Edit: The save to core data method is above - it calls occasionWithDate method and checks if the date exists already when the dateOfEvent attribute is NSString. Because I need to sort by ascending dates in the table view, I have changed the dateOfEvent to be a NSDate format

To get the current date and time, I'm putting this code in the save method:

Date *date = [NSEntityDescription insertNewObjectForEntityForName:@"Date" inManagedObjectContext:context];

date.dateOfEvent = [NSDate date];
transaction.dates = date; 

That is giving me the current date and time. What I want is for the user to select a date using the UIDatePicker and whatever date is selected, for that to be saved as the dateOfEvent attribute of the Date entity which I can then use in the Sections of the Table view.

Answer 1

To get NSDate from your UIDatePicker object use UIDatePicket date property.

date

The date displayed by the date picker.

@property(nonatomic, retain) NSDate *date

Discussion The default is the date when the UIDatePicker object is created. The date is ignored in the mode UIDatePickerModeCountDownTimer; for that mode, the date picker starts at 0:00. Setting this property does not animate the date picker by spinning the wheels to the new date and time; to do that you must use the setDate:animated: method.

check Apple UIDatePicker documentation