Question

I’m very new to memory management, and I have a question regarding saving a date pickers date. This is the code that I use to save inputted text:

NSString *filePath = [self dataFilePath];
if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
    NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath];
    event1Field.text = [array objectAtIndex:0];
    event2Field.text = [array objectAtIndex:1];
}

How would I edit this to save a date pickers date rather than inputted text? And how would I edit the viewDidLoad method as well? I usually just input the data of the picker in there, like this:

- (void)viewDidLoad {
    NSDate *now = [NSDate date];
    [datePicker setDate:now animated:YES];
}

But I’m not sure how I would go about loading it into it’s saved state. Sorry if these are dumb questions, I’m still pretty new and learning as I go.

Thank you!

Answer 1

The simplest way to persist data is to use NSUserDefaults which is provided by the Foundation framework. It’s basically just a key value store which allows you to save small amounts of data.

First and foremost, saving data from a date picker looks something akin to this:

// NSUserDefaults is a singleton instance and access to the store is provided 
// by the class method, +standardUserDefaults
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

// Let's pull the date out of our picker
NSDate *selectedDate = [self.datePicker date];

// Store the date object into the user defaults. The key argument expects a 
// string and should be unique. I usually prepend any key with the name 
// of the class it's being used in.
// Savvy programmers would pull this string out into a constant so that 
// it could be accessed from other classes if necessary.
[defaults setObject:selectedDate forKey:@"DatePickerViewController.selectedDate"];

Now when we want to pull this data back out and populate our date picker, we could do something like the following…

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Get the date. We're going to use a little shorthand instead of creating 
    // a variable for the instance of `NSUserDefaults`.
    NSDate *storedDate = [[NSUserDefaults standardUserDefaults] objectForKey:@"DatePickerViewController.selectedDate"];

    // Set the date on the date picker. We're passing `NO` to `animated:` 
    // because we're performing this before the view is on screen, but after
    // it has been loaded.
    [self.datePicker setDate:storedDate animated:NO];
}