InkWell,

Form, and

TextField
are examples of stateful widgets. Stateful widgets
subclass

StatefulWidget.

A widget’s state is stored in a State object,
separating the widget’s state from its appearance.
The state consists of values that can change, like a
slider’s current value or whether a checkbox is checked.
When the widget’s state changes,
the state object calls setState(),
telling the framework to redraw the widget.

Creating a stateful widget

What's the point?

A stateful widget is implemented by two classes:
a subclass of StatefulWidget and a subclass of State.

The state class contains the widget’s mutable state and
the widget’s build() method.

When the widget’s state changes, the state object calls
setState(), telling the framework to redraw the widget.