MaterialPageRoute builder is called three times during route lifecycle

[lukef]

It appears that builder functions for MaterialPageRoute (as well as PageRouteBuilder) is being called for the following lifecycle events:

• Before enter
• Entered
• Exit (if you dismiss the route)

I'm not sure if this is normal or if you can differentiate between each of the events but it could lead to code execution issues. It may just be unclear documentation (or I totally missed something?).

Example:

new MaterialPageRoute<Null>(settings: routeSettings, builder: (BuildContext context) {
  print("Test message");
  return SomeWidget();
});

"Test message" will appear in the log three times.

[GRouslan]

MaterialPageRoute builds every time I put a finger in a TextField, so the cursor runs to the starting position and I am unable to put the cursor in the middle of a text:

MaterialPageRoute:

Navigator.of(context).push(new MaterialPageRoute<Null>(
      builder: (BuildContext context) {
        return new EditPersonDialog(person);
      },
    ));

TextField:

new TextField(
                maxLines: null,
                controller: textEditingController,
                onChanged: (text) => ...)

[GRouslan]

Dirty workaround (copy-paste works with it as well):

class MyRoot extends MaterialPageRoute<Null> {

  final Person person;

  MyRoot(this.person) : super(builder: (BuildContext context) {
    return new EditPersonDialog(person);
  },);

  @override
  Color get barrierColor => super.barrierColor;

  Widget cashed;

  @override
  Widget buildPage(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
    if (cashed == null) {
      cashed = super.buildPage(context, animation, secondaryAnimation);
    }
    return cashed;
  }

  @override
  bool get maintainState => super.maintainState;

  @override
  Duration get transitionDuration => super.transitionDuration;
}

[Hixie]

Build methods can get called a lot; build methods should be idempotent (that is, calling them repeatedly should have no side-effects). Why is it that rebuilding the route is clearing your text field? Are you recreating the textEditingController in the build method, maybe?

[GRouslan]

This is my code essence, I have no idea where I bring side-effects:

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter issue #14124',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter issue #14124'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(title),
      ),
      body: new Center(
        child: new FlatButton(
          onPressed: () => openDialog(context),
          child: new Text('Open dialog'),
        ),
      ),
    );
  }

  void openDialog(BuildContext context) {
    Navigator
        .of(context)
        .push(new MaterialPageRoute<Null>(builder: (BuildContext context) {
      return new MyDialog();
    }));
  }
}

class MyDialog extends StatelessWidget {
  final TextEditingController textEditingController;

  MyDialog()
      : textEditingController = new TextEditingController(text: 'initial');

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: new Padding(
      padding: const EdgeInsets.all(16.0),
      child: new Center(
        child: new TextField(
          maxLines: null,
          controller: textEditingController,
        ),
      ),
    ));
  }
}

[Hixie]

You have a stateless widget that has state (a text editing controller).

[GRouslan]

Sorry, I have to read documentation again.

[goderbauer]

As far as I can tell there's nothing actionable in this issue (as has been pointed out, build methods should be idempotent). Closing this for now, but feel free to reopen with additional information if there's more to it.

[goderbauer]

See also: #11655

[hbirdGit]

Build methods can get called a lot; build methods should be idempotent (that is, calling them repeatedly should have no side-effects). Why is it that rebuilding the route is clearing your text field? Are you recreating the textEditingController in the build method, maybe?

"build methods should be idempotent " clear my all misunderstandings. Thank you

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.