screen flickering with every keyboard stroke in Flutter

So what you need to do: Completely remove the onChanged property of the textField. It is not needed. You can get the current text in the textField from its controller. And in the onPressed function of the icon button check if controller.text is not equal to "" and if yes call the _sendMessage function. updatedCode:

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

  @override
  State<ChatGroupLayout> createState() => _ChatGroupLayoutState();
}

    class _ChatGroupLayoutState extends State<ChatGroupLayout> {
      final fieldText = TextEditingController();

      void clearText() {
        fieldText.clear();
      }

      void _sendMessage() async {
        final user = await FirebaseAuth.instance.currentUser;
        final userData = await FirebaseFirestore.instance
            .collection('users')
            .doc(user?.uid)
            .get();

        FirebaseFirestore.instance
            .collection('groupsChat')
            .doc('groupsChat')
            .collection('P1HSu0cjsQSyIKZ7ZiX6a74rwzU2')
            .add({
          'text': fieldText.text.trim(),
          'time': Timestamp.now(),
          'userid': user?.uid,
          'displayname': userData['displayname']
        });
      }

      static final _formKey = GlobalKey<FormState>();

      @override
      Widget build(BuildContext context) {
        return SafeArea(
          child: Scaffold(
            backgroundColor: Colors.grey.shade700,
            appBar: AppBar(
              backgroundColor: Colors.black,
              title: ListTile(
                onTap: () => showBarModalBottomSheet(
                    context: context,
                    builder: (context) => const GroupDetailsScreen()),
                tileColor: Colors.black,
                title: const Center(child: Text('Group Chat')),
                subtitle: const Center(child: Text('323 in this Group')),
              ),
              actions: [
                IconButton(
                    onPressed: () {}, icon: const Icon(Icons.favorite_border)),
                IconButton(
                  onPressed: () {},
                  icon: const Icon(Icons.exit_to_app),
                ),
              ],
            ),
            body: Column(
              children: [
                Expanded(
                  child: ChatGroupScreen(),
                ),
                Row(
                  children: [
                    Expanded(
                      child: Padding(
                        padding: const EdgeInsets.only(
                            left: 6, bottom: 6, right: 0, top: 5),
                        child: TextField(
                          key: _formKey,
                          controller: fieldText,
                          decoration: InputDecoration(
                            prefixIcon: IconButton(
                              icon: const Icon(
                                Icons.emoji_emotions_outlined,
                                color: Colors.white,
                              ),
                              onPressed: () {},
                            ),
                            suffixIcon: IconButton(
                              icon: const Icon(
                                Icons.attach_file,
                                color: Colors.white,
                              ),
                              onPressed: () {},
                            ),
                            filled: true,
                            fillColor: Colors.black,
                            hintText: 'type a message',
                            border: OutlineInputBorder(
                              borderRadius: BorderRadius.circular(6),
                              borderSide: const BorderSide(
                                width: 0,
                                style: BorderStyle.none,
                              ),
                            ),
                            contentPadding: EdgeInsets.all(20),
                          ),
                        ),
                      ),
                    ),
                    IconButton(
                        icon: Icon(Icons.send),
                        onPressed: () {
                          if (fieldText.text != "") {
                            _sendMessage();
                            clearText();
                          }
                        }),
                  ],
                ),
              ],
              //TextInput
            ),
          ),
        );
      }
    }