Why when I tap textField in stateless widget it will rebuild widget? - flutter

Question

when I tap text widget it will rebuild widget, I don't know why
main.dart
import 'package:flutter/material.dart';
import './loading.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
print("Main Build.");
return MaterialApp(
title: 'chat',
home: LoadingPage(),
);
}
}
loadingPage.dart
import 'package:flutter/material.dart';
import 'signUp/inputPhone.dart';
class LoadingPage extends StatelessWidget {
#override
Widget build(BuildContext context) {
print("Loading Page Build.");
FocusScope.of(context).requestFocus(new FocusNode());
new Future.delayed(Duration(seconds: 3), () {
print("Flutter APP UI");
Navigator.of(context).pushReplacement(
new MaterialPageRoute(builder: (context) => InputPhone()));
});
return Stack(
fit: StackFit.expand,
alignment: AlignmentDirectional.center,
children: <Widget>[
Image.asset("images/bgPatten.png", fit: BoxFit.cover),
Image.asset("images/logoAll.png"),
],
);
}
}
inputPhone.dart
import 'package:flutter/material.dart';
class InputPhone extends StatelessWidget {
#override
Widget build(BuildContext context) {
print("input phone build");
return GestureDetector(
onTap: () {
print("Tap Outside.");
FocusScope.of(context).requestFocus(new FocusNode());
},
child: Scaffold(
appBar: new AppBar(
title: Text("STEP 1"),
leading: Container(),
elevation: 0.0,
),
body: TextField(),
),
);
}
}
but when I change main.dart home to InputPhone(), it will not happen
sorry I really don't know what's wrong with my code
please give me some help... thank you all... :)

Answer 1

When you tap TextField Widget, it makes the keyboard show up. and When keyboard shows up your screen size is changed. And just because your screen size is changed the widgets that you are using needs to build again.
And this thing will happen with both StatefulWidget and StatelessWidget.
You can verify this behavior by making State of an StatefulWidget extend WidgetsBindingObserver class. The method didChangeMetrics() will be called when your KeyBoard shows up by tapping on TextField.
This happens because of scaffold's resizeToAvoidBottomPadding which is by default true.
Refer following comments from the source code.
/// If true the [body] and the scaffold's floating widgets should size
/// themselves to avoid the onscreen keyboard whose height is defined by the
/// ambient [MediaQuery]'s [MediaQueryData.viewInsets] `bottom` property.
///
/// For example, if there is an onscreen keyboard displayed above the
/// scaffold, the body can be resized to avoid overlapping the keyboard, which
/// prevents widgets inside the body from being obscured by the keyboard.
///
/// Defaults to true.
final bool resizeToAvoidBottomInset;

Answer 2

In StatelessWidget the Build method is being called for many reasons like (screen rotation, animations, scrolling...) so that you should use StatefulWidget