Custom input and FormField widgets

We have seen how the Form and FormField widgets help with input manipulation and validation. Also, we know that Flutter comes with a series of input widgets that are FormField variants containing helper functions such as save and validate.

The extensibility and flexibility of Flutter is everywhere in the framework, so creating your own custom input fields is entirely possible.

Creating custom inputs

Creating a custom input in Flutter is as simple as creating a normal widget and including the methods described earlier. We normally do this by extending the FormField<inputType> widget, where inputType is the value type of the input widget.

So, the typical process is as follows:

1. Create a custom widget that extends StatefulWidget (to keep track of the value) and accepts input from the user by encapsulating another input widget, or by customizing the whole process, such as by using gestures.
2. Create a widget that extends FormField...