Can I create a custom text field and keyboard for iOS w/o subclassing UIControl?

Question

My app will require the user to input chemistry formulas (H2O, Na^2+), and since subscripts and superscripts may make the typing process confusing for the user, I have decided to make a custom keyboard.

When the user types in a number as a subscript, it should be displayed as a subscript on the screen. The only way I've found to do this is using NSAttributedString, which apparently only works with CoreText. Since I can't have CoreText in a UITextField, I need to create a custom text field as well. I was looking into UITextView, but the documentation reads that the font styles must be consistent throughout the text, meaning I can't have subscripts.

Do I need to subclass UIControl for both cases and start from scratch? Or is there an alternative class I can start with that already has some of the properties of keyboard/textfield?

Answer 1

Yes, you need to create your own subclass of UIView.

But you can easily support keyboard input by adopting the UIKeyInput protocol, overriding canBecomeFirstResponder so it returns YES and adding a UITapGestureRecognizer:

    [self addGestureRecognizer:
     [[UITapGestureRecognizer alloc] initWithTarget:self
                                             action:@selector(becomeFirstResponder)]];

I you want to allow the user to select ranges of text and use autocorrection, that's harder: you need to adopt the protocol UITextInput.

Customizing the keyboard is really simple:

• either, you override inputAccessoryView which allow you to display a custom view attached to the keyboard,
• either, you override inputView so it returns a custom view that will be displayed in place of the keyboard.