In this example, we’ll demonstrate how to set an icon on a TextField widget to appear at the start and end of input in a Flutter application. The most effective technique to display the data type of a TextField is through icons. For further details, see the example below:

Set the TextField Icon at the Head and Tail of Input

	TextField(
	decoration: InputDecoration(
	icon: Icon(Icons.lock), //icon at head of input
	//prefixIcon: Icon(Icons.people), //you can use prefixIcon property too
	//prefisIcon sets Icon inside the TextField border, 'icon' sets outside border.
	suffixIcon: Icon(Icons.remove_red_eye) //icon at tail of input
	)
	)

view raw gistfile1.txt hosted with by GitHub

Full Code Example:

	import 'package:flutter/material.dart';
	void main(){
	runApp(MyApp());
	}
	class MyApp extends StatelessWidget{
	@override
	Widget build(BuildContext context) {
	return MaterialApp(
	home: Home(),
	);
	}
	}
	class Home extends StatefulWidget{
	@override
	_HomeState createState() => _HomeState();
	}
	class _HomeState extends State<Home> {
	TextEditingController username = TextEditingController();
	TextEditingController password = TextEditingController();
	@override
	void initState() {
	username.text = ""; //innitail value of text field
	password.text = "";
	super.initState();
	}
	@override
	Widget build(BuildContext context) {
	return Scaffold(
	appBar: AppBar(
	title: Text("Icons on TextField"),
	backgroundColor: Colors.deepOrangeAccent,
	),
	body: Container(
	padding: EdgeInsets.all(20),
	child: Column(
	children: [
	TextField(
	controller: username,
	decoration: InputDecoration(
	labelText: "Username",
	icon: Icon(Icons.people), //icon at head of input
	)
	),
	TextField(
	controller: password,
	decoration: InputDecoration(
	icon: Icon(Icons.lock), //icon at head of input
	//prefixIcon: Icon(Icons.people), //you can use prefixIcon property too.
	labelText: "Password",
	suffixIcon: Icon(Icons.remove_red_eye) //icon at tail of input
	)
	),
	],
	),
	)
	);
	}
	}

view raw gistfile1.txt hosted with by GitHub

Output Screenshot:

How to add icon inside the field
You need to use the prefixIcon attribute instead of an icon like

TextField(
  decoration: InputDecoration(prefixIcon: Icon(Icons.mail)),
)