Passing data and delegation

Question

I have got a question about delegation. I am fairly new to programming and I have just managed my first exercise-project in which I use delegation. All it is, is a Parent View Controller that calls a Child View Controller which has a text field and a button in it. I write something in that text field, press the button, the Child VC is dismissed and it passes the text back. It then gets displayed in a label on the Parent. I have got a couple of animations for the transition. It all works. Here are some pictures first and the code:

This is my parent view controller:

Click the button and the Child appears:

Write something in the text field and press the button to pass it back:

The data is displayed on a label in the parent view controller.

Here are the files for this:

ParentViewController.h

#import <UIKit/UIKit.h>
#import "ChildViewController.h"

@interface ParentViewController : UIViewController <ChildViewControllerDelegate>

@property (strong, nonatomic) IBOutlet UILabel *label;

@end

ParentViewController.m

@implementation ParentViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}
- (IBAction)Pressed:(id)sender {
    ChildViewController *childViewController = [[ChildViewController alloc]init];
    [self displayContentController:childViewController];
    childViewController.delegate = self;

}

- (void) displayContentController: (UIViewController*) content {
    [self addChildViewController:content];
    content.view.frame = CGRectMake(0, 115, 320, 240);
    content.view.backgroundColor = [UIColor redColor];


    CATransition *transition = [CATransition animation];
    transition.duration = 1;
    transition.type = kCATransitionPush;
    transition.subtype = kCATransitionFromLeft;
    [transition setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut]];
    [content.view.layer addAnimation:transition forKey:nil];
    [self.view addSubview:content.view];
    [content didMoveToParentViewController:self];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];

}

-(void) passDataBack:(NSString *)data{

    self.label.text = data;

}

@end

ChildViewController.h

#import <UIKit/UIKit.h>

@protocol ChildViewControllerDelegate <NSObject>

-(void)passDataBack:(NSString*)data;

@end

@interface ChildViewController : UIViewController
@property (strong, nonatomic) IBOutlet UITextField *txtfield;

@property (nonatomic, weak) id <ChildViewControllerDelegate> delegate;
- (IBAction)passingBack:(id)sender;

@property NSString *data;

@end

ChildViewController.m

#import "ChildViewController.h"

@interface ChildViewController ()

@end

@implementation ChildViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];

}


- (IBAction)passingBack:(id)sender {

    NSString *itemToPassBack = self.txtfield.text;

    [self.delegate passDataBack:itemToPassBack];

    [self.childViewControllers lastObject];


    [self willMoveToParentViewController:nil];

    [UIView animateWithDuration:1
                          delay:0.0
         usingSpringWithDamping:1
          initialSpringVelocity:1
                        options:UIViewAnimationOptionCurveEaseIn
                     animations:^{

                         self.view.frame = CGRectMake(-320, 115, 320, 240);

                     } completion:^(BOOL complete){

                             [self.view removeFromSuperview];
                             [self removeFromParentViewController];
                     }];

}

@end

Regarding the code, there are a couple of things I am not sure about, as I am learning I copied a lot of code etc... so for example I am not sure as to how to animate the child controller back using the same method as I used to animate it in, or if it matters and what is best practice etc... also, I get a strange message in the console: "Unknown class ViewController in Interface Builder file." but it works, so I am not sure why it's there. For the record, I haven't used the storyboard, only xibs.

My question though is the following: I would like to have the button to dismiss the Child View Controller not in the Child View Controller but in the parent, like so:

And that's where I am lost. I just don't know how to trigger the method to pass data back from the Parent View Controller. Can anyone help? many thanks