IOS numberpad add done button not clickable

Hey, all, I have one problem. I want to add done button to numeric keypad in ios and you for this following code. The problem is button not clickable after appearing. In my window I have table view with textfields.

- (void) hello:(id) sender
{
    NSLog(@"helloooo");
}
 
- (void)addButtonToKeyboard
{
    if (!self.doneButton)
    {
        self.doneButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [self.doneButton addTarget:self action:@selector(hello:) forControlEvents:UIControlEventTouchUpInside];
    }
    self.doneButton.adjustsImageWhenHighlighted = NO;
    [self.doneButton setTitle:@"DONE" forState:UIControlStateNormal];
    [self.doneButton.titleLabel setFont:[UIFont systemFontOfSize:16.0]];
    [self.doneButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [self.doneButton setTitleColor:[UIColor blackColor] forState:UIControlStateHighlighted];
 
    // locate keyboard view
    if ([[[UIApplication sharedApplication] windows] count] <= 1) return;
    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];
    UIView* keyboard;
    for(int i=0; i<[tempWindow.subviews count]; i++)
    {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard found, add the button
        if ([[keyboard description] hasPrefix:@"<UIPeripheralHost"] == YES)
        {
            BOOL isPortrait = UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation);
            self.doneButton.frame = CGRectMake(((isPortrait)?0:-1),((int) (keyboard.frame.size.height*3)/4) + ((isPortrait)?0:1),(int) keyboard.frame.size.width/3-1, (isPortrait)?60:40);
            [keyboard addSubview:self.doneButton];
        }
        //This code will work on iOS 8.0
        else if([[keyboard description] hasPrefix:@"<UIInputSetContainerView"] == YES)
        {
            for(int i = 0 ; i < [keyboard.subviews count] ; i++)
            {
                UIView* hostkeyboard = [keyboard.subviews objectAtIndex:i];
                if([[hostkeyboard description] hasPrefix:@"<UIInputSetHost"] == YES)
                {
                    BOOL isPortrait = UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation);
                    self.doneButton.frame = CGRectMake(((isPortrait) ? 0 : -1),((int) (hostkeyboard.frame.size.height*3)/4) + ((isPortrait) ? 0 : 1),(int) hostkeyboard.frame.size.width/3-1, (isPortrait) ? 60 : 40);
                    [hostkeyboard addSubview:self.doneButton];
                }
            }
        }
        else{}
    }
}
 
 
-(void)textFieldDidBeginEditing:(UITextField *)textField
{
    [self performSelector:@selector(addButtonToKeyboard) withObject:nil afterDelay:0.75];
}