# UITextInputStringTokenizer A base implementation of the text-input tokenizer protocol. ``` @MainActor class UITextInputStringTokenizer ``` ## Overview If you want to take advantage of this base implementation of the [`UITextInputTokenizer`](/documentation/UIKit/UITextInputTokenizer) protocol, you should subclass this class and handle application-specific directions and granularities affected by layout. When you instantiate a class you must supply the document class that’s adopting the [`UITextInput`](/documentation/UIKit/UITextInput) protocol for your application. ### Subclassing notes When you subclass [`UITextInputStringTokenizer`](/documentation/UIKit/UITextInputStringTokenizer), override all [`UITextInputTokenizer`](/documentation/UIKit/UITextInputTokenizer) methods, calling the superclass implementation (`super`) when method parameters aren’t affected by layout. For example, the subclass needs a custom implementation of all methods for line granularity. For the left direction, it needs to decide whether left corresponds at a given position to forward or backward, and then call `super` passing in the storage direction ([`UITextStorageDirection`](/documentation/UIKit/UITextStorageDirection)). ## Topics ### Initializing a tokenizer [`init(textInput:)`](/documentation/UIKit/UITextInputStringTokenizer/init(textInput:)) Returns an object initialized with the document object that directly communicates with the text input system. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)