Edit field by code

In order to add an editable text box. E.g.: To ask the username, use the next code:

UITextField* textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 200, 300, 50)];
textField.delegate = self;
textField.placeholder = @"<Enter Your Username>";
textField.textAlignment = UITextAlignmentCenter;
[self.view addSubview: textField];
[textField release];

And add the delegate <UITextFieldDelegate> to your viewController:
- (BOOL)textFieldShouldReturn:(UITextField *)textField{
	//Do something with textField.text;
	[textField resignFirstResponder];

    return YES;
}