How can I catch event when a text field is exiting focus (on blur) in Flutter?

Question

I look into TextFormField, the fields here isn't what I need:

• onChanged (called after each key pressed, I need when the user has already complete and exit the TextFormField focus)
• onEditingComplete (called after user press on Done key or similar, but user may exit TextFormField focus without tapping those button)
• onSave (called after calling form.save(). But I need to do this after user finish editing, to let user know that the app does "auto-correcting" to what the user entered)
• validator (also called on form.validate(), right before form.save(). not what I needed)

I need that when user exit the focus (dismissing the keyboard or tapping into another text field), I do a processing to let user see that their input is being adjusted and processed to the "correct one". How can I catch such event?

Answer 1

By using FocusNode class, you add a focus listener and can catch focus change.

By using Focus class, you just wrap TextField and add a onFocusChange parameter.

[Solution 1]

• add a define FocusNode instance

FocusNode focusNode = FocusNode();

• add a listener of FocusNode at initState.

focusNode.addListener(() {
      print('1:  ${focusNode.hasFocus}');
    });

• add a FocusNode instance to TextField's focusNode parameter.

TextField(
      focusNode: focusNode,
    )

[Solution 2]

• Wrap TextField by Focus widget

Focus(
  child: TextField(),
  onFocusChange: (hasFocus) {
    print('2:  $hasFocus');
  },
)

[Example Full Code]

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();
  @override
  void initState() {
    super.initState();
    focusNode.addListener(() {
      print(focusNode.hasFocus);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: _buildBody(),
    );
  }

  Widget _buildBody() {
    return TextField(
      focusNode: focusNode,
    );
  }
}