title: Paste event on TextFormField doesn't work with onChange Flutter
body: <p>I'd tried for some weeks to put a callback function when i paste some text in a TextFormField to modify/format the text i'd paste.</p>
  
  <p>I used a TextEditingController with the SetState function, change the callback function with a variable on SetState but I should be doing something wrong.</p>
  
  <p>Sometimes it works but not everytime. To reproduce the bug, you can select all, write some caracters, paste some text, cut, write, select all and paste, mostly i have to make a change o trigger an event and then it works.
  What i'm doing wrong ?</p>
  
  <p>Thanks in advance</p>
  
  <pre><code>import 'dart:convert';
  import 'package:flutter/material.dart';
  
  void main() {
    runApp(MyApp());
  }
  
  class MyApp extends StatelessWidget {
    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          // This is the theme of your application.
          //
          // Try running your application with "flutter run". You'll see the
          // application has a blue toolbar. Then, without quitting the app, try
          // changing the primarySwatch below to Colors.green and then invoke
          // "hot reload" (press "r" in the console where you ran "flutter run",
          // or simply save your changes to "hot reload" in a Flutter IDE).
          // Notice that the counter didn't reset back to zero; the application
          // is not restarted.
          primarySwatch: Colors.blue,
          // This makes the visual density adapt to the platform that you run
          // the app on. For desktop platforms, the controls will be smaller and
          // closer together (more dense) than on mobile platforms.
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      );
    }
  }
  
  class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
  
    // This widget is the home page of your application. It is stateful, meaning
    // that it has a State object (defined below) that contains fields that affect
    // how it looks.
  
    // This class is the configuration for the state. It holds the values (in this
    // case the title) provided by the parent (in this case the App widget) and
    // used by the build method of the State. Fields in a Widget subclass are
    // always marked "final".
  
    final String title;
  
    @override
    _MyHomePageState createState() =&gt; _MyHomePageState();
  }
  
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    int _counter = 0;
    TextEditingController orderBoxController = new TextEditingController();
  
    void _incrementCounter() {
      setState(() {
        // This call to setState tells the Flutter framework that something has
        // changed in this State, which causes it to rerun the build method below
        // so that the display can reflect the updated values. If we changed
        // _counter without calling setState(), then the build method would not be
        // called again, and so nothing would appear to happen.
        _counter++;
      });
    }
    void _myTextHasChanged(String texto) {
      setState(() {
        orderBoxController.text = 'i changed';
      });
    }
  
  
    @override
    Widget build(BuildContext context) {
      // This method is rerun every time setState is called, for instance as done
      // by the _incrementCounter method above.
      //
      // The Flutter framework has been optimized to make rerunning build methods
      // fast, so that you can just rebuild anything that needs updating rather
      // than having to individually change instances of widgets.
      return Scaffold(
        appBar: AppBar(
          // Here we take the value from the MyHomePage object that was created by
          // the App.build method, and use it to set our appbar title.
          title: Text(widget.title),
        ),
        body: Center(
          // Center is a layout widget. It takes a single child and positions it
          // in the middle of the parent.
          child: Column(
            // Column is also a layout widget. It takes a list of children and
            // arranges them vertically. By default, it sizes itself to fit its
            // children horizontally, and tries to be as tall as its parent.
            //
            // Invoke "debug painting" (press "p" in the console, choose the
            // "Toggle Debug Paint" action from the Flutter Inspector in Android
            // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
            // to see the wireframe for each widget.
            //
            // Column has various properties to control how it sizes itself and
            // how it positions its children. Here we use mainAxisAlignment to
            // center the children vertically; the main axis here is the vertical
            // axis because Columns are vertical (the cross axis would be
            // horizontal).
            mainAxisAlignment: MainAxisAlignment.center,
            children: &lt;Widget&gt;[
              Expanded(
                child: new TextFormField(
                  controller: orderBoxController,
                  onChanged: _myTextHasChanged,
                  maxLines: null,
                  cursorColor: Colors.black,
                  decoration: new InputDecoration(
                      border: InputBorder.none,
                      focusedBorder: InputBorder.none,
                      enabledBorder: InputBorder.none,
                      errorBorder: InputBorder.none,
                      disabledBorder: InputBorder.none,
                      contentPadding: EdgeInsets.only(
                          left: 15,
                          bottom: 11,
                          top: 11,
                          right: 15),
                      hintText: 'Write here'),
                  style: TextStyle(
                    fontFamily: 'Segoe UI',
                  ),
                ),
              ),
            ],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: Icon(Icons.add),
        ), // This trailing comma makes auto-formatting nicer for build methods.
      );
    }
  }
  
  </code></pre>
  
  <p>I finally solved my problem by using InputFormatter in my TextFormField</p>
  
  <p><code>inputFormatters: [OrderInputFormatter()],</code></p>