To learn how to implement a signature painter in Flutter,
see Collin’s answer on Custom Paint.

How do I build custom widgets?

In Android, you typically subclass View, or use a pre-existing view,
to override and implement methods that achieve the desired behavior.

In Flutter, build a custom widget by composing
smaller widgets (instead of extending them).
It is somewhat similar to implementing a custom ViewGroup
in Android, where all the building blocks are already existing,
but you provide a different behavior—for example,
custom layout logic.

For example, how do you build a CustomButton that takes a label in
the constructor? Create a CustomButton that composes a ElevatedButton with
a label, rather than by extending ElevatedButton:

Then use CustomButton, just as you’d use any other Flutter widget:

Intents

What is the equivalent of an Intent in Flutter?