build method

  1. @override
Widget build(
  1. BuildContext context
)
override

Describes the part of the user interface represented by this widget.

The framework calls this method in a number of different situations. For example:

This method can potentially be called in every frame and should not have any side effects beyond building a widget.

The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.

Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor, the given BuildContext, and the internal state of this State object.

The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. The BuildContext argument is always the same as the context property of this State object and will remain the same for the lifetime of this object. The BuildContext argument is provided redundantly here so that this method matches the signature for a WidgetBuilder.

Design discussion

Why is the build method on State, and not StatefulWidget?

Putting a Widget build(BuildContext context) method on State rather than putting a Widget build(BuildContext context, State state) method on StatefulWidget gives developers more flexibility when subclassing StatefulWidget.

For example, AnimatedWidget is a subclass of StatefulWidget that introduces an abstract Widget build(BuildContext context) method for its subclasses to implement. If StatefulWidget already had a build method that took a State argument, AnimatedWidget would be forced to provide its State object to subclasses even though its State object is an internal implementation detail of AnimatedWidget.

Conceptually, StatelessWidget could also be implemented as a subclass of StatefulWidget in a similar manner. If the build method were on StatefulWidget rather than State, that would not be possible anymore.

Putting the build function on State rather than StatefulWidget also helps avoid a category of bugs related to closures implicitly capturing this. If you defined a closure in a build function on a StatefulWidget, that closure would implicitly capture this, which is the current widget instance, and would have the (immutable) fields of that instance in scope:

// (this is not valid Flutter code)
class MyButton extends StatefulWidgetX {
  MyButton({super.key, required this.color});

  final Color color;

  @override
  Widget build(BuildContext context, State state) {
    return SpecialWidget(
      handler: () { print('color: $color'); },
    );
  }
}

For example, suppose the parent builds MyButton with color being blue, the $color in the print function refers to blue, as expected. Now, suppose the parent rebuilds MyButton with green. The closure created by the first build still implicitly refers to the original widget and the $color still prints blue even through the widget has been updated to green; should that closure outlive its widget, it would print outdated information.

In contrast, with the build function on the State object, closures created during build implicitly capture the State instance instead of the widget instance:

class MyButton extends StatefulWidget {
  const MyButton({super.key, this.color = Colors.teal});

  final Color color;
  // ...
}

class MyButtonState extends State<MyButton> {
  // ...
  @override
  Widget build(BuildContext context) {
    return SpecialWidget(
      handler: () { print('color: ${widget.color}'); },
    );
  }
}

Now when the parent rebuilds MyButton with green, the closure created by the first build still refers to State object, which is preserved across rebuilds, but the framework has updated that State object's widget property to refer to the new MyButton instance and ${widget.color} prints green, as expected.

See also:

  • StatefulWidget, which contains the discussion on performance considerations.

Implementation

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBarClass.appBarWithBack(context, "settings"),
    body: SingleChildScrollView(
      child: Container(
          padding: const EdgeInsets.all(20),
          decoration: AppStyles.boxDecorationContainer(),
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  // IMAGEN DEL USUARIO
                  ClipOval(
                    child: Image.network(
                      imageUrl,
                      fit: BoxFit.cover,
                      width: 140,
                      height: 140,
                    ),
                  ),
                  // COLUMNA PARA EL NOMBRE Y EL MAIL DEL USUARIO
                  Padding(
                    padding: const EdgeInsets.only(left: 20),
                    child: Column(
                      // SE ALINEA A LA IZQUIERDA
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: [
                        // NOMBRE USUARIO
                        Text(
                          returnName(),
                          style: const TextStyle(
                            fontSize: 32,
                            fontWeight: FontWeight.bold,
                            color: AppColors.purpleIntroColor,
                          ),
                        ),

                        // MAIL USUARIO, SI EL NOMBRE DE USUARIO ES LARGO SE SALTA DE LINEA
                        Container(
                          constraints: const BoxConstraints(maxWidth: 200),
                          child: Text(
                            mail,
                            style: const TextStyle(
                              fontSize: 18,
                              color: AppColors.purpleIntroColor,
                              overflow: TextOverflow.visible,
                            ),
                          ),
                        ),
                      ],
                    ),
                  ),
                ],
              ),

              const SizedBox(height: 20),

              // GENERAL
              Align(
                alignment: Alignment.centerLeft,
                child: Internationalization.internationalization
                    .localizedTextOnlyKey(
                  context,
                  "general",
                  style: const TextStyle(
                      fontSize: 20,
                      fontWeight: FontWeight.bold,
                      color: AppColors.lightVioletColor),
                ),
              ),

              // IDIOMAS
              SettingsContainer(
                functionArrow: () {
                  AlertUtil.showChangeLanguague(context);
                },
                name: Internationalization.internationalization.getLocalizations(context, "languages"),
                icon: Icons.language,
                tooltip: Internationalization.internationalization.getLocalizations(context, "select_languages"),
              ),

              const SizedBox(height: 10),

              // NOTIFICACIONES
              SettingsContainer(
                functionArrow: () {
                  // IR A LA PANTALLA DE NOTIFICACIONES
                  ChangeScreen.changeScreen(const NotificationScreen(), context);
                },
                name: Internationalization.internationalization.getLocalizations(context, "notification"),
                icon: Icons.notifications,
                tooltip: Internationalization.internationalization.getLocalizations(context, "select_notification"),
              ),

              const SizedBox(height: 20),

              Align(
                alignment: Alignment.centerLeft,
                child: Internationalization.internationalization
                    .localizedTextOnlyKey(
                  context,
                  "time_configuration",
                  style: const TextStyle(
                      fontSize: 20,
                      fontWeight: FontWeight.bold,
                      color: AppColors.lightVioletColor),
                ),
              ),

              // CONFIGURAR TIMER
              SettingsContainer(
                functionArrow: () {
                  // IR A LA PANTALLA DE NOTIFICACIONES
                  ChangeScreen.changeScreen(const ConfigureTimerScreen(), context);
                },
                name: Internationalization.internationalization.getLocalizations(context, "configure_timer"),
                icon: Icons.timer,
                tooltip: Internationalization.internationalization.getLocalizations(context, "configure_timer"),
              ),

              const SizedBox(height: 10),

              // CONFIGURAR INSPECCION
              SettingsContainer(
                functionArrow: () {
                  // IR A LA PANTALLA DE CONFIGURAR INSPECCION
                  ChangeScreen.changeScreen(const ConfigureInspectionScreen(), context);
                },
                name: Internationalization.internationalization.getLocalizations(context, "inspection_title"),
                icon: Icons.hourglass_top_rounded,
                tooltip: Internationalization.internationalization.getLocalizations(context, "inspection_title"),
              ),

              const SizedBox(height: 20),

              Align(
                alignment: Alignment.centerLeft,
                child: Internationalization.internationalization
                    .localizedTextOnlyKey(
                  context,
                  "account",
                  style: const TextStyle(
                      fontSize: 20,
                      fontWeight: FontWeight.bold,
                      color: AppColors.lightVioletColor),
                ),
              ),

              // PERFIL
              SettingsContainer(
                functionArrow: () {
                  ChangeScreen.changeScreen(const MyProfileScreen(), context);
                }, // CUANDO PULSE IRA A LA PANTALLA DE PERFIL
                name: Internationalization.internationalization.getLocalizations(context, "my_profile"),
                icon: Icons.person,
                tooltip: Internationalization.internationalization.getLocalizations(context, "my_profile"),
              ),

              const SizedBox(height: 20),

              Align(
                alignment: Alignment.centerLeft,
                child: Internationalization.internationalization
                    .localizedTextOnlyKey(
                  context,
                  "advanced_options_title",
                  style: const TextStyle(
                      fontSize: 20,
                      fontWeight: FontWeight.bold,
                      color: AppColors.lightVioletColor),
                ),
              ),

              // OPCIONES AVANZADAS
              SettingsContainer(
                functionArrow: () {
                  // IR A LA PANTALLA DE OPCIONES AVANZADAS
                  ChangeScreen.changeScreen(const AdvancedOptionsScreen(), context);
                },
                name: Internationalization.internationalization
                    .getLocalizations(context, "advanced_options_title"),
                icon: Icons.tune,
                tooltip: Internationalization.internationalization
                    .getLocalizations(context, "advanced_options_title"),
              ),

              const SizedBox(height: 30),

              // GITHUB
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: [
                  IconClass.iconMaker(
                      context, Icons.account_circle_sharp, "github", 40),
                  TextButton(
                      onPressed: () async {
                        // CUANDO PULSE IRA A MI GITHUB
                        const url = 'https://github.com/estelaV9';
                        if (await canLaunch(url)) {
                          await launch(url);
                        } else {
                          throw 'No se pudo abrir la URL';
                        } // VERIFICA SI LA URL ES VALIDA
                      },
                      child: Internationalization.internationalization
                          .localizedTextOnlyKey(context, "name_github",
                              style: AppStyles.darkPurpleAndBold(30)))
                ],
              ),
            ],
          )),
    ),
  );
}