助力跨平台应用开发利器：Flutter MaterialApp控件详解

2024-02-20 05:17:30

MaterialApp：构建应用的基础

MaterialApp 是 Flutter 中一个非常重要的控件，它是构建整个应用程序的基础。它为应用程序提供了必要的配置信息，如应用程序的标题、主题、导航和路由等。

定义与功能

MaterialApp 的定义如下：

class MaterialApp extends StatelessWidget {
  const MaterialApp({
    Key? key,
    this.title = '',
    this.home,
    this.theme,
    this.darkTheme,
    this.themeMode = ThemeMode.system,
    this.locale,
    this.localizationsDelegates,
    this.localeListResolutionCallback,
    this.supportedLocales = const <Locale>[Locale('en', 'US')],
    this.debugShowCheckedModeBanner = true,
    this.shortcuts,
    this.actions,
    this.restorationScopeId,
    this.scrollBehavior,
  }) : super(key: key);

  /// The title of the application.
  ///
  /// This title is used for accessibility purposes. It appears in
  /// the operating system task switcher and other application
  /// metadata requests.
  ///
  /// See [debugDefaultTargetPlatformOverride] for a way to override
  /// the default title for testing.
  final String title;

  /// The widget for the default route of the application.
  ///
  /// The application is considered to be stateless until the first
  /// frame for the given widget is built.
  ///
  /// See [Navigator.push] for the semantics of this widget and more
  /// explanations about its relationship with [Navigator].
  ///
  /// In a typical Material application, this will be a
  /// [Scaffold] widget that contains other routes as its children.
  final Widget? home;

  /// The overall theme of the application.
  ///
  /// The initial theme for the application. When this is set, a
  /// [Theme] widget will be created based on this theme and
  /// automatically included at the root of the widget tree, which will
  /// affect all the descendant widgets.
  ///
  /// This theme can be overridden for a specific subtree of widgets
  /// by providing a [Theme] widget with a different theme closer
  /// in the widget tree.
  ///
  /// Typically this will be a [ThemeData] object, but a [Theme]
  /// object may also be provided.
  final ThemeData? theme;

  /// The overall dark theme of the application.
  ///
  /// The initial dark theme for the application. When this is set, a
  /// [Theme] widget will be created based on this theme and
  /// automatically included at the root of the widget tree, which will
  /// affect all the descendant widgets, when the [themeMode] is set to
  /// [ThemeMode.dark] or [ThemeMode.system] and the platform is in dark
  /// mode.
  ///
  /// This theme can be overridden for a specific subtree of widgets
  /// by providing a [Theme] widget with a different theme closer
  /// in the widget tree.
  ///
  /// Typically this will be a [ThemeData] object, but a [Theme]
  /// object may also be provided.
  final ThemeData? darkTheme;

  /// The mode that determines which theme to use.
  ///
  /// If [darkTheme] is set, the current theme will depend on the
  /// [ThemeMode] that's used. If [themeMode] is [ThemeMode.system],
  /// the current theme will be [darkTheme] if the platform is in dark
  /// mode, otherwise [theme]. If [themeMode] is [ThemeMode.light], the
  /// current theme will always be [theme]. If [themeMode] is
  /// [ThemeMode.dark], the current theme will always be [darkTheme].
  ///
  /// The effective theme can be overridden for a specific subtree of
  /// widgets by providing a [Theme] widget with a different [themeMode]
  /// closer in the widget tree.
  ///
  /// Defaults to [ThemeMode.system].
  ///
  /// This theme mode can also be controlled using the
  /// [MediaQueryData.platformBrightness] parameter of [MediaQueryData]
  /// or [ThemeData.platformBrightness].
  final ThemeMode themeMode;

  /// The locale of the application.
  ///
  /// This locale is used to determine the language and formatting
  /// conventions used in the application, as well as the
  /// measurements and directionality used.
  final Locale? locale;

  /// The delegates for providing localized resources for this
  /// application.
  ///
  /// See [Localizations] for more information.
  ///
  /// In this list, later delegates will take precedence over earlier
  /// ones, as will entries in the [GlobalMaterialLocalizations]. The
  /// entries from the [GlobalMaterialLocalizations] can be overridden
  /// by providing a [MaterialLocalizations] instance in this list.
  ///
  /// The default value of this list includes [DefaultMaterialLocalizations]
  /// and [GlobalMaterialLocalizations].
  ///
  /// This list must not contain null entries.
  final Iterable<LocalizationsDelegate<dynamic>>? localizationsDelegates;

  /// The callback used to resolve the locale list of this
  /// application.
  ///
  /// This callback provides a way to override the locale list which can
  /// be resolved by the [Localizations] object.
  ///
  /// It should return a list of locales which can be used by this
  /// application and which can also be used in the [localeListResolutionCallback]
  /// of the [WidgetsApp] or the [CupertinoApp] which creates this
  /// [MaterialApp].
  final LocaleListResolutionCallback? localeListResolutionCallback;

  /// The list of locales which this application should support.
  ///
  /// This list must not contain null entries. It must also contain all
  /// the locales which are present in [GlobalMaterialLocalizations].
  ///
  /// If the [locale] property is specified, then it must also be
  /// present in this list.
  ///
  /// If the [localizationsDelegates] property is specified, then their
  /// locales must also be present in this list.
  ///
  /// The default value is a list containing a single entry for the locale
  /// 'en_US'.
  final List<Locale> supportedLocales;

  /// Whether to display a banner indicating that the application is
  /// running in debug mode.
  ///
  /// By default, a debug banner is displayed above the [home] widget
  /// when Flutter is in debug mode, i.e. when asserts are enabled.
  ///
  /// This banner will be displayed even if a [debugDefaultTargetPlatformOverride]
  /// is set, although the banner will contain the name of the overridden
  /// platform.
  final bool debugShowCheckedModeBanner;

  /// The list of shortcuts defined in this application.
  ///
  /// See [WidgetsApp.shortcuts] for more information.
  final List<ShortcutActivator>? shortcuts;

  /// The list of actions defined in this application.
  ///
  /// See [WidgetsApp.actions] for more information.
  final List<Action<Intent>>? actions;

  /// The ID used to identify the restoration scope associated with
  /// this application.
  ///
  /// When a [Navigator] is pushed into the [WidgetsApp] created by
  /// this application, a new restoration scope is created with the
  /// specified ID.
  ///
  /// See [RestorationScope] for more information.
  final String? restorationScopeId;

  /// The scroll behavior used for this application.
  ///
  /// By default, [ScrollConfiguration.of(context)] will return a
  /// [ScrollConfiguration] with [ScrollBehavior] of type
  /// [GlowingOverscrollIndicator], which shows an overscroll glow when
  /// the scrollable widget (e.g. ListView, SingleChildScrollView, etc.)
  /// is scrolled past its edge.
  ///
  /// You can customize the [ScrollBehavior] for this application
  /// by providing a [ScrollBehavior] subclass in this property.
  final ScrollBehavior? scrollBehavior;
}