How to transfer textfield's label to top of prefix Icon instead of text

Question

In flutter's textField when we use prefixIcon and label, in focus mode label's animation transfers to the top of the text (not to the top of the icon). I don't want to use prefix instead of prefixIcon because prefix hides when textField is not on focus mode. I need my prefix always visible. Like these images from material designs text fields part:

Answer 1

Although there are some fix position value,
here is my implementation,

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  FocusNode _focusNode = FocusNode();
  bool textEditHasFocus = false;
  @override
  void initState() {
    super.initState();
    _focusNode.addListener(() {
      setState(() {
        textEditHasFocus = _focusNode.hasFocus;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: _buildBody(),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }

  Widget _buildBody() {
    return Container(
      decoration: BoxDecoration(color: Colors.white),
      padding: new EdgeInsets.symmetric(
        vertical: 40.0,
        horizontal: 20,
      ),
      child: Stack(
        clipBehavior: Clip.none,
        children: <Widget>[
          Container(
            child: TextField(
              focusNode: _focusNode,
              decoration: InputDecoration(
                // hintText: textEditHasFocus ? '' : 'Label',
                // hintStyle: TextStyle(
                //   color: Colors.grey,
                // ),
                border: OutlineInputBorder(),
                focusedBorder: OutlineInputBorder(),
                contentPadding: EdgeInsets.only(left: 40),
              ),
            ),
          ),
          AnimatedPositioned(
            duration: Duration(milliseconds: 200),
            left: textEditHasFocus ? 10 : 40,
            top: textEditHasFocus ? -10 : 13,
            child: InkWell(
              onTap: () {
                _focusNode.requestFocus();
              },
              child: Container(
                padding: EdgeInsets.only(left: 3),
                color: Colors.white,
                child: Text('Label'),
              ),
            ),
          ),
          Positioned.fill(
            child: Align(
              alignment: Alignment.centerLeft,
              child: Container(
                padding: EdgeInsets.only(left: 10),
                color: Colors.transparent,
                child: Icon(Icons.favorite),
              ),
            ),
          ),
        ],
      ),
    );
  }
}

Answer 2

Your material designs text fields part link provided I try same design and your need when you focused on TextField the labelText is display on the prefixIcon In lots of their is not correct solution I found

Refer prefixIcon Widget documentaion here and see the given example

Refer prefix Widget documentation here

Refer InputDecoration class here

Try below code when icon is display ouside of the TextField

TextFormField(
      decoration: InputDecoration(
        prefixIcon: Icon(
          Icons.favorite,
        ),
        border: OutlineInputBorder(),
        labelText: 'Brand Description',
        hintText: 'Brand Description Here',
      ),
    ),

Your result screen Without focus->

Your result screen With focus->