How do you retrieve and listen to TextField changes in Flutter?

WHAT THIS TESTS: This question evaluates whether you understand Flutter's imperative state management for text input and whether you respect widget lifecycle boundaries. Even though it sounds like a junior topic, senior engineers are expected to mention disposal, distinguish between one-off callbacks and persistent controllers, and know when to use each pattern.

A GOOD ANSWER COVERS: A strong answer walks through four steps in order. First, create a TextEditingController, typically in a State object as a final field or in initState. Second, assign it to the TextField or TextFormField via the controller parameter. Third, listen to changes by calling addListener on the controller. Inside the listener you read controller.text to get the current string or inspect controller.value for selection and composition metadata. Fourth and non-negotiable, override the State's dispose method and call controller.dispose to detach listeners and free resources. A senior candidate should also note that onChanged is acceptable for ephemeral UI reactions but is not the standard approach when you need programmatic access to the text outside the build method or across multiple widgets.

COMMON WRONG ANSWERS: The biggest red flag is suggesting onChanged as the standard pattern for retrieving and listening to text values. While onChanged fires on every keystroke, it is just a callback and does not give you a way to read the current value imperatively later. Another red flag is forgetting disposal entirely, which leaks memory and leaves stale listeners in the widget tree. A third warning sign is confusing the controller with focus nodes or trying to manage text state via setState inside onChanged without understanding the performance implications.

LIKELY FOLLOW-UPS: An interviewer might ask how you would clear or preset the text programmatically, which you do by mutating controller.text or controller.selection. They might ask about the difference between TextField and TextFormField, where the latter integrates with FormState and validators. They could also ask how to debounce search queries derived from text input, which tests your ability to combine a controller with a Timer or stream.

ONE CONCRETE EXAMPLE: Imagine a search screen with a TextField. You create a TextEditingController named _searchController in your State class. In initState, you add a listener that prints _searchController.text every time the user types. The TextField is built as TextField with the controller set to _searchController and a hint decoration. When the user navigates away and the widget is destroyed, your dispose method calls _searchController.dispose so the listener does not outlive the widget.