ShowHidePasswordView

import 'package:flutter/material.dart';

class ShowHidePasswordView extends StatefulWidget {
  @override
  _ShowHidePasswordViewState createState() => _ShowHidePasswordViewState();
}

class _ShowHidePasswordViewState extends State<ShowHidePasswordView> {
  bool  _passwordVisible;
  TextEditingController _userPasswordController= TextEditingController();

  @override
  void initState() {
    _passwordVisible = false;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TextFormField(
          keyboardType: TextInputType.text,
          controller: _userPasswordController,
          obscureText: !_passwordVisible,//This will obscure text dynamically
          decoration: InputDecoration(
            labelText: 'Password',
            hintText: 'Enter your password',
            // Here is key idea
            suffixIcon: IconButton(
              icon: Icon(
                // Based on passwordVisible state choose the icon
                _passwordVisible
                    ? Icons.visibility
                    : Icons.visibility_off,
                color: Theme.of(context).primaryColorDark,
              ),
              onPressed: () {
                // Update the state i.e. toogle the state of passwordVisible variable
                setState(() {
                  _passwordVisible = !_passwordVisible;
                });
              },
            ),
          ),
        ),
      ),
    );
  }
}