iOS7 - Storing NSDate value from button press to use later - ios

Question

I need to capture the result of NSDate when a button is pressed, so I can use it later on in the app.
What is the best way / code to do this?
Update
Sorry for not including more information. New to this site, and wasn't aware of protocol.
So I understand how to respond to a button press. However, whilst I have written the result of NSDate to the timeStampLabel, what I really want to do is save the result of NSDate at that point to a key? or similar in order that I can use it later. I require the data to be accessible to a different class, however, have no need for the data to persist if the app was closed entirely (i.e. swiped up and off the screen).
The code I currently have is:
- (IBAction)tripButton:(id)sender {
NSDate *date = [NSDate date];
self.timeStampLabel.text = [NSString stringWithFormat:#"%# ", date];
}

Answer 1

You can declare the variable in your App Delegate:
#interface AppDelegate : UIResponder <UIApplicationDelegate, UINavigationControllerDelegate> {
#property (strong, nonatomic) UIWindow *window;
#property (strong, nonatomic) UINavigationController *navigationController;
#property (nonatomic) NSDate* timeStamp;
#end
Then when you need to access the variable from any class, get an instance of the App Delegate...
First declare the variable right after the implementation in that class's .m:
#implementation ClassViewController
AppDelegate *mainDelegate;
then initialize it in viewDidLoad:
- (void)viewDidLoad {
mainDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
and now you can access it from anywhere. In this case...
- (IBAction)tripButton:(id)sender {
NSDate *date = [NSDate date];
self.timeStampLabel.text = [NSString stringWithFormat:#"%# ", date];
mainDelegate.timeStamp = date;
}
Then in another class, for example:
- (NSDate*)getTimeStamp {
return mainDelegate.timeStamp;
}

Answer 2

So, there are three methods (that I know of) to deal with passing information across different view controllers in iOS.
Lindsey Scott's answer suggests storing the information as properties on the App Delegate and reaching into the app delegate to set/retrieve the data.
Duncan C's answer explains my preferred method, using singletons.
The third method that I know of is passing the information directly between the views that need it. This is simple to manage if you just need to pass the data from one view that is presented immediately before the view you're passing the information to.
Assuming you're using segues, you'd do something like this...
Given ViewController1 and ViewController2, give ViewController2 an NSDate public property to store the date you're passing to it. We'll call it passedDate in this example. We'll also give ViewController1 a property (private, probably) to store the date temporarily, we'll call it dateToPass in this example. Both properties should be strong.
Now, in ViewController1, the IBAction that handles the button press will look like this:
-(IBAction)buttonPressed:(id)sender {
self.dateToPass = [NSDate date];
[self performSegueWithIdentifier:#"segueMySegue" sender: self];
}
So now the button press saves the date to a property and calls the segue. As a note, we don't have to do both actions in this single button press. The main thing that's important is saving the date on the button press to a property so you can access it later. You can perform the segue however/whenever you want.
Now, to actually pass the data, we're going to override the prepareForSegue: method:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:#"segueMySegue"]) {
ViewController2 *dest = [segue destinationViewController];
dest.passedDate = self.dateToPass;
}
}
Now we've set the property passedDate on the next view controller to point to the dateToPass date object we set on the button press. We can access this property in ViewController2 and do with it whatever we need to do.

Answer 3

You have 2 different issues:
How to save a date value for later
How to pass data between different objects in your app.
The first can be solved by making an NSDate or NSTimeInterval property.
The second can be solved various ways. I recommend creating a data container singleton. A singleton is an object that is designed to only be created once in the lifetime of a program and then used throughout. Typically you create a class method called something like sharedDataObject that creates the object the first time you need it, and saves it in a static variable:
header:
#interface DataContainerObject: NSObject
#property (nonatomic, strong) NSDate *dateToSave;
+ (DataContainerObject *) sharedDataObject;
#end
Implementation:
#implementation DataContainerOBject:
+ (DataContainerObject *) sharedDataObject;
{
static DataContainerObject* _sharedDataObject;
if (_sharedDataObject == nil)
_sharedDataObject = [[DataContainerObject alloc] init];
return _sharedDataObject;
}