Explanation:

When working with Flutter forms, the FormKey and currentState are crucial elements. Here’s an explanation of how they work and an example to understand it better:

• FormKey: The FormKey is a unique identifier for the form. It is used to uniquely identify a particular form when working with multiple forms in a single screen.
• currentState: The currentState property is used to get the current state of the form. It provides access to various methods and properties related to the form’s state, such as validate() and save().

Now, let’s consider an example scenario where the currentState is null after initializing a Form widget with a FormKey:

<form_key_example.dart>

// Importing required dependencies
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

// Defining a Flutter app
class MyApp extends StatelessWidget {
  final _formKey = GlobalKey();

  // Function called when form is submitted
  void _submitForm() {
    if (!_formKey.currentState!.validate()) {
      return;
    }
    _formKey.currentState!.save();
    // Process form data further...
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Form Key Example')),
        body: Center(
          child: Form(
            key: _formKey,
            child: Column(
              children: [
                TextFormField(
                  validator: (value) {
                    if (value!.isEmpty) {
                      return 'Please enter a value';
                    }
                    return null;
                  },
                ),
                ElevatedButton(
                  onPressed: _submitForm,
                  child: Text('Submit'),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

In this example:

1. We define a Flutter app with a _formKey as a private member of the MyApp class.
2. The _formKey is assigned a new instance of GlobalKey<FormState>. This represents the unique identifier for the form.
3. Inside the _submitForm() function, we use the currentState to validate and save the form data. If validation fails, it returns early. Otherwise, the form data is processed further.
4. In the build() method, we wrap the Form widget around a Column, containing a TextFormField and an ElevatedButton.
5. We set the key property of the Form widget to the _formKey we defined earlier. This associates the form with the respective key and allows us to access its state.
6. When the ElevatedButton is pressed, it calls the _submitForm() function to handle the form submission.

Thus, by using the FormKey and accessing the currentState, we can validate and save form data in Flutter.