OnFieldSubmitted does not take the text value provided using TextFormField in Flutter

Question

I am trying to get the data from the text field. While pressing the send button I need the data provided in text field to be stored up in '_message'. This is not working as expected thus my Map(newMessage) does not hold any value and thus my message list is empty. I need some solution so that my _message hold the value provided using OnFieldSubmitted.

Even while running the app it only prints (send 'value written in text box') and does not print the _message provided using OnFeildSubmitted.

 Padding(
        padding: EdgeInsets.all(12.0),
        child: Row(
          children: <Widget>[
            Expanded( 
                child: TextFormField(
              controller: _controller,
              onFieldSubmitted: (String _message){
                print("on submit  "+_message);
                Map<String,dynamic> newMessage = {
                  "type": "string",
                  "content": _message,
                  "from": "me",


                };
                List<dynamic> newList = _listOfMessages;
                newList.add(newMessage);

                setState(() {
                  _listOfMessages = newList;
                });
                _controller.clear();

              },
              decoration: InputDecoration(
                hintText: "Type your message here",
              ),
            )),
            Padding(
              padding: EdgeInsets.all(8.0),

              child: Center(
                child: IconButton(
                icon: Icon(Icons.send,
                color: Colors.blue),

                onPressed: () {
                  print("send " + _controller.text);
                },
              ),
              )
            )
          ],

Answer 1

You need to implement this:

/// In `State` class body
String _message;
final _formKey = GlobalKey<FormState>();

/// In `build` method body.
Form(
  key: _formKey,        // <-- This is required.
  child: TextFormField(
    controller: _controller,
    onSave: (value) {
      _message = value;
    }
  ),
),

IconButton(
  icon: Icon(
    Icons.send,
    color: Colors.blue
  ),
  onPressed: () {
    if(_formKey.currentState.validate()) {
      _formKey.currentState.save(); // This call triggers `onSave` callbacks.
      _sendMesage(_message);        // Handle _message variable.
    }
  },
,