How to access the parent view controller?

I am using this code to push a view controller in ViewControllerA:

DatePickerViewController *viewController = [[DatePickerViewController alloc] initWithNibName:@"DateP开发者_如何学运维ickerViewController" bundle:nil];
NSMutableArray *info = [[NSMutableArray alloc] initWithObjects:@"Exam Duration",nil];
[viewController setInfo:info];
[info release];
[self.navigationController pushViewController:viewController animated:YES];
[viewController release];

In the DatePickerViewController that is slid in, it has a text field. In ViewControllerA how can I get the value of this text field once the viewWillDisappear method is fired, it's to save data.

There are several ways to do this. Best would be to use a delegate pattern or a notification system.

Which one you choose depends on your whishes. If you just want the 'parent controller' to know about the value, use a delegate method.

Using delegates or notifications creates a loosely coupled structure and makes reusable classes possible.

EDIT: Some sample code. Beware: untested and from the top of my head!

DatePickerViewController.h

@protocol DatePickerViewControllerDelegate
    -(void)datePicker:(DatePickerViewController *)picker pickedDate:(NSDate *)date;
@end

DatePickerViewController.m

- (void)viewWillDisappear:(BOOL)animated {
    [self.delegate datePicker:self pickedDate:theDate]; //Delegate is an ivar
    [super viewWillDisappear:animated];
}

ViewControllerA.m

//
DatePickerViewController *viewController = [[DatePickerViewController alloc] initWithNibName:@"DatePickerViewController" bundle:nil];
NSMutableArray *info = [[NSMutableArray alloc] initWithObjects:@"Exam Duration",nil];
[viewController setInfo:info];
[info release];
[viewController setDelegate:self]; // Set the delegate of the date picker
[self.navigationController pushViewController:viewController animated:YES];
[viewController release];
//

-(void)datePicker:(DatePickerViewController *)picker pickedDate:(NSDate *)date; {
     //Deal with the new date here
}