trying to add done button to Numeric keyboard

I'm trying to add a "done" button to the UIKeyboadnumpad, but with no success. What's wrong in my code?

the keyboard don't have the done button

@implementation DemoViewController

- (void)loadView {
    self.view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].applicationFrame];
    self.view.backgroundColor = [UIColor groupTableViewBackgroundColor];

    textField = [[UITextField alloc] initWithFrame:CGRectMake(10, 200, 300, 26)];
    textField.borderStyle = UITextBorderStyleRoundedRect;
    textField.keyboardType = UIKeyboardTypeNumberPad;
    textField.returnKeyType = UIReturnKeyDone;
    textField.textAlignment = UITextAlignmentLeft;
    textField.text = @"12345";
    [self.view addSubview:textField];

    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(keyboardWillShow:) 
                                                 name:UIKeyboardWillShowNotification 
                                               object:nil];
}

- (void)keyboardWillShow:(NSNotification *)note {  
    // create custom button
    UIButton *doneButton = [UIButton buttonWithType:UIButtonTypeCustom];
    doneButton.frame = CGRectMake(0, 163, 106, 53);
    doneButton.adjustsImageWhenHighlighted = NO;
    [doneButton setImage:[UIImage imageNamed:@"DoneUp.png"] forState:UIControlStateNormal];
    [doneButton setImage:[UIImage imageNamed:@"DoneDown.png"] forState:UIControlStateHighlighted];
    [doneButton addTarget:self action:@selector(doneButton:) forControlEvents:UIControlEventTouchUpInside];

    // locate keyboard view
    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:0];
    UIView* keyboard;
    for(int i=0; i<[tempWindow.subviews count]; i++) {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard view found; add the custom button to it
        if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 3.2) {