How to change TextFormField background color when focus?

I have a TextFormField and I want to change the background color from #EFEFEF to white when the user presses on the field to type, here is my custom widget:

class TextFieldWidget extends StatelessWidget {
  final TextEditingController controller;
  final bool isEmail;
  const TextFieldWidget({
    Key? key,
    required this.controller,
    required this.isEmail,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      keyboardType: isEmail ? TextInputType.emailAddress : TextInputType.text,
      obscureText: !isEmail,
      controller: controller,
      decoration: InputDecoration(
        hintText: isEmail ? 'Enter your email' : 'Enter your password',
        filled: true,
        fillColor: const Color(0xffefefef),
        focusColor: Colors.white,
        border: OutlineInputBorder(borderRadius: BorderRadius.circular(5)),
        prefixIcon: Icon(
          isEmail ? Icons.email : Icons.lock,
          color: const Color(0xFF1273EB),
        ),
      ),
      validator: (value) {
        if (isEmail) {
          if (value!.isEmpty) {
            return 'Email can\'t be empty';
          } else if (!value.contains('@')) {
            return 'Please enter a valid email address';
          }
        } else if (!isEmail) {
          if (value!.isEmpty) {
            return 'Password can\'t be empty';
          } else if (value.length < 6) {
            return 'Password must be at least 6 characters long';
          }
        }
        return null;
      },
    );
  }
}

When the screen displays I have the #EFEFEF color, but when I press on the text field it doesn't turn to another color (white in my case).

To change the background color of the textfield once it has focus, you can use a FocusNode and check whether it hasFocus:

First, accept a focusnode in your custom widget:

class TextFieldWidget extends StatefulWidget {
  final TextEditingController controller;
  final bool isEmail;
  final FocusNode focusNode;
  const TextFieldWidget({
    Key? key,
    required this.controller,
    required this.isEmail,
    required this.focusNode,
  }) : super(key: key);

then, in the custom widgets initState add a listener the update the state once there's focus:

  @override
void initState() {
super.initState();
widget.focusNode.addListener(() {
setState(() {});
});
}

and in your TextFied:

decoration: InputDecoration(
        fillColor: widget.focusNode.hasFocus ? Color(0xffefefef) : Colors.grey,

Here's a complete runnable snippet:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  MyApp({Key? key}) : super(key: key);
  final _focusNode = FocusNode();
  final _textController = TextEditingController();
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'focus node',
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: TextFieldWidget(
            controller: _textController,
            focusNode: _focusNode,
            isEmail: false,
          ),
        ),
      ),
    );
  }
}

class TextFieldWidget extends StatefulWidget {
  final TextEditingController controller;
  final bool isEmail;
  final FocusNode focusNode;
  const TextFieldWidget({
    Key? key,
    required this.controller,
    required this.isEmail,
    required this.focusNode,
  }) : super(key: key);

  @override
  State<TextFieldWidget> createState() => _TextFieldWidgetState();
}

class _TextFieldWidgetState extends State<TextFieldWidget> {
  @override
  Widget build(BuildContext context) {
    return TextFormField(
      focusNode: widget.focusNode,
      keyboardType:
          widget.isEmail ? TextInputType.emailAddress : TextInputType.text,
      obscureText: !widget.isEmail,
      controller: widget.controller,
      decoration: InputDecoration(
        fillColor: widget.focusNode.hasFocus ? Color(0xffefefef) : Colors.grey,
        hintText: widget.isEmail ? 'Enter your email' : 'Enter your password',
        filled: true,
        focusColor: Colors.white,
        border: OutlineInputBorder(borderRadius: BorderRadius.circular(5)),
        prefixIcon: Icon(
          widget.isEmail ? Icons.email : Icons.lock,
          color: const Color(0xFF1273EB),
        ),
      ),
      validator: (value) {
        if (widget.isEmail) {
          if (value!.isEmpty) {
            return 'Email can\'t be empty';
          } else if (!value.contains('@')) {
            return 'Please enter a valid email address';
          }
        } else if (!widget.isEmail) {
          if (value!.isEmpty) {
            return 'Password can\'t be empty';
          } else if (value.length < 6) {
            return 'Password must be at least 6 characters long';
          }
        }
        return null;
      },
    );
  }

  @override
  void initState() {
    super.initState();
    widget.focusNode.addListener(() {
      print('focusNode.hasFocus: ${widget.focusNode.hasFocus}');
      setState(() {});
    });
  }
}

See also

• https://stackoverflow.com/questions/49341856/how-to-detect-when-a-textfield-is-selected-in-flutter