Localizations class

Defines theLocale for itschild and the localized resources that thechild depends on.

Defining localized resources

This following class is defined in terms of theDartintl package. Using theintlpackage isn't required.

class MyLocalizations {  MyLocalizations(this.locale);  final Locale locale;  static Future<MyLocalizations> load(Locale locale) {    return initializeMessages(locale.toString())      .then((void _) {        return MyLocalizations(locale);      });  }  static MyLocalizations of(BuildContext context) {    return Localizations.of<MyLocalizations>(context, MyLocalizations)!;  }  String title() => Intl.message('<title>', name: 'title', locale: locale.toString());  // ... more Intl.message() methods like title()}

A class based on theintl package imports a generated message catalog that providestheinitializeMessages() function and the per-locale backing store forIntl.message().The message catalog is produced by anintl tool that analyzes the source code forclasses that containIntl.message() calls. In this case that would just be theMyLocalizations class.

One could choose another approach for loading localized resources and looking them up whilestill conforming to the structure of this example.

Loading localized resources

Localized resources are loaded by the list ofLocalizationsDelegatedelegates. Each delegate is essentially a factory for a collectionof localized resources. There are multiple delegates because there aremultiple sources for localizations within an app.

Delegates are typically simple subclasses ofLocalizationsDelegate thatoverrideLocalizationsDelegate.load. For example a delegate for theMyLocalizations class defined above would be:

// continuing from previous example...class _MyDelegate extends LocalizationsDelegate<MyLocalizations> {  @override  Future<MyLocalizations> load(Locale locale) => MyLocalizations.load(locale);  @override  bool isSupported(Locale locale) {    // in a real implementation this would only return true for    // locales that are definitely supported.    return true;  }  @override  bool shouldReload(_MyDelegate old) => false;}

Each delegate can be viewed as a factory for objects that encapsulate a setof localized resources. These objects are retrieved withby runtime type withLocalizations.of.

TheWidgetsApp class creates aLocalizations widget so most appswill not need to create one. The widget app'sLocalizations delegates canbe initialized withWidgetsApp.localizationsDelegates. TheMaterialAppclass also provides alocalizationsDelegates parameter that's justpassed along to theWidgetsApp.

Obtaining localized resources for use in user interfaces

Apps should retrieve collections of localized resources withLocalizations.of<MyLocalizations>(context, MyLocalizations),where MyLocalizations is an app specific class defines one function perresource. This is conventionally done by a static.of method on thecustom localized resource class (MyLocalizations in the example above).

For example, using theMyLocalizations class defined above, one wouldlookup a localized title string like this:

// continuing from previous example...MyLocalizations.of(context).title()

IfLocalizations were to be rebuilt with a newlocale thenthe widget subtree that corresponds toBuildContextcontext wouldbe rebuilt after the corresponding resources had been loaded.

This class is effectively anInheritedWidget. If it's rebuilt witha newlocale or a different list of delegates or any of itsdelegates'LocalizationsDelegate.shouldReload() methods returns true,then widgets that have created a dependency by callingLocalizations.of(context) will be rebuilt after the resourcesfor the new locale have been loaded.

TheLocalizations widget also instantiatesDirectionality in order tosupport the appropriateDirectionality.textDirection of the localizedresources.

Inheritance

Constructors

Localizations({Key?key,requiredLocalelocale,requiredList<LocalizationsDelegate>delegates,Widget?child,boolisApplicationLevel =false}): Create a widget from which localizations (like translated strings) can be obtained.
Localizations.override({Key?key,requiredBuildContextcontext,Locale?locale,List<LocalizationsDelegate>?delegates,Widget?child}): Overrides the inheritedLocale orLocalizationsDelegates forchild.
factory

Properties

child→Widget?: The widget below this widget in the tree.
final
delegates→List<LocalizationsDelegate>: This list collectively defines the localized resources objects that canbe retrieved withLocalizations.of.
final
hashCode→int: The hash code for this object.
no setterinherited
isApplicationLevel→bool: Whether this is the main localizations widget that represents the app'slocale.
final
key→Key?: Controls how one widget replaces another widget in the tree.
finalinherited
locale→Locale: The resources returned byLocalizations.of will be specific to this locale.
final
runtimeType→Type: A representation of the runtime type of the object.
no setterinherited

Methods

createElement()→StatefulElement: Creates aStatefulElement to manage this widget's location in the tree.
inherited
createState()→State<Localizations>: Creates the mutable state for this widget at a given location in the tree.
override
debugDescribeChildren()→List<DiagnosticsNode>: Returns a list ofDiagnosticsNode objects describing this node'schildren.
inherited
debugFillProperties(DiagnosticPropertiesBuilderproperties)→ void: Add additional properties associated with the node.
override
noSuchMethod(Invocationinvocation)→ dynamic: Invoked when a nonexistent method or property is accessed.
inherited
toDiagnosticsNode({String?name,DiagnosticsTreeStyle?style})→DiagnosticsNode: Returns a debug representation of the object that is used by debuggingtools and byDiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevelminLevel =DiagnosticLevel.info})→String: A string representation of this object.
inherited
toStringDeep({StringprefixLineOne ='',String?prefixOtherLines,DiagnosticLevelminLevel =DiagnosticLevel.debug,intwrapWidth =65})→String: Returns a string representation of this node and its descendants.
inherited
toStringShallow({Stringjoiner =', ',DiagnosticLevelminLevel =DiagnosticLevel.debug})→String: Returns a one-line detailed description of the object.
inherited
toStringShort()→String: A short, textual description of this widget.
inherited

Operators

operator ==(Objectother)→bool: The equality operator.
inherited

Static Methods

localeOf(BuildContextcontext)→Locale: The locale of the Localizations widget for the widget tree thatcorresponds toBuildContextcontext.
maybeLocaleOf(BuildContextcontext)→Locale?: The locale of the Localizations widget for the widget tree thatcorresponds toBuildContextcontext.
of<T>(BuildContextcontext,Typetype)→ T?: Returns the localized resources object of the giventype for the widgettree that corresponds to the givencontext.

Flutter
widgets
Localizations class

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