InkWellButton

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  static const String _title = 'Flutter Code Sample';

  var text = "";

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(
          title: Row(
            children: [
              const Text(_title),
              const SizedBox(
                width: 20,
              ),
              Expanded(
                child: TextField(
                  decoration: const InputDecoration(
                    filled: true,
                    fillColor: Colors.white,
                    hintText: "Enter text here...",
                  ),
                  onChanged: (value) => setState(
                    () {
                      text = value;
                    },
                  ),
                ),
              )
            ],
          ),
        ),
        body: Center(
          child: MyButton(
            onTap: text.isNotEmpty ? () {} : null,
          ),
        ),
      ),
    );
  }
}

class MyButton extends StatelessWidget {
  final void Function()? onTap;

  const MyButton({Key? key, this.onTap}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: 40,
      height: 40,
      child: Material(
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(8),
        ),
        type: MaterialType.button,
        color: onTap == null ? Colors.grey : Colors.deepPurple,
        child: InkWell(
          child: Icon(
            Icons.send,
            color: onTap == null ? Colors.grey[400] : Colors.white,
          ),
          onTap: onTap,
        ),
      ),
    );
  }
}