Adding UIToolbar to input accessory view on some text fields

In my quest for my first iPhone app I have posted about the correct way to handle the return key on the iOS keyboard. Now I need to figure out the toolbar above the keyboard with prev/next and done buttons. I have been working with an example from the following site: Input Accessory View

The example works, but I want to use a UIToolbar and UIBarButtonItem's instead of just a regular view with buttons. I have tried various combinations, none work yet. Here is what I have so far.

Header:

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UITextFieldDelegate>
{
    UITextField* txtActiveField;
    UIToolbar* keyboardToolbar;
    UIBarButtonItem* btnDone;
    UIBarButtonItem* btnNext;
    UIBarButtonItem* btnPrev;
}

@property (nonatomic, strong) IBOutlet UITextField* firstNameTextField;
@property (nonatomic, strong) IBOutlet UITextField* lastNameTextField;
@property (nonatomic, strong) IBOutlet UITextField* cityTextField;

@property (nonatomic, strong) UITextField* txtActiveField;
@property (nonatomic, strong) UIToolbar* keyboardToolbar;
@property (nonatomic, strong) UIBarButtonItem* btnDone;
@property (nonatomic, strong) UIBarButtonItem* btnNext;
@property (nonatomic, strong) UIBarButtonItem* btnPrev;

-(void)createInputAccessoryView;

@end

Source:

#import "ViewController.h"

@implementation ViewController

@synthesize firstNameTextField = _firstNameTextField;
@synthesize lastNameTextField = _lastNameTextField;
@synthesize cityTextField = _cityTextField;

@synthesize txtActiveField = _txtActiveField;
@synthesize keyboardToolbar = _keyboardToolbar;
@synthesize btnDone = _btnDone;
@synthesize btnNext = _btnNext;
@synthesize btnPrev = _btnPrev;

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

#pragma mark - View lifecycle

- (voi