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Diffstat (limited to 'documentation/architecture/architecture-events.asciidoc')
| -rw-r--r-- | documentation/architecture/architecture-events.asciidoc | 36 |
1 files changed, 8 insertions, 28 deletions
diff --git a/documentation/architecture/architecture-events.asciidoc b/documentation/architecture/architecture-events.asciidoc index e497ce5e94..c3f7b51468 100644 --- a/documentation/architecture/architecture-events.asciidoc +++ b/documentation/architecture/architecture-events.asciidoc @@ -7,17 +7,17 @@ layout: page [[architecture.events]] = Events and Listeners -Vaadin offers an event-driven programming model for handling user interaction. +Vaadin Framework offers an event-driven programming model for handling user interaction. When a user does something in the user interface, such as clicks a button or selects an item, the application needs to know about it. Many Java-based user interface frameworks follow the __Event-Listener pattern__ (also known as the Observer design pattern) to communicate user input to the application logic. So -does Vaadin. The design pattern involves two kinds of elements: an object that +does Vaadin Framework. The design pattern involves two kinds of elements: an object that generates ("fires" or "emits") events and a number of listeners that listen for the events. When such an event occurs, the object sends a notification about it to all the listeners. In a typical case, there is only one listener. -Events can serve many kinds of purposes. In Vaadin, the usual purpose of events +Events can serve many kinds of purposes. In Vaadin Framework, the usual purpose of events is handling user interaction in a user interface. Session management can require special events, such as time-out, in which case the event would actually be the lack of user interaction. Time-out is a special case of timed or scheduled @@ -32,28 +32,23 @@ listener). Most components that have related events define their own event class and the corresponding listener class. For example, the [classname]#Button# has [classname]#Button.ClickEvent# events, which can be listened to through the -[classname]#Button.ClickListener# interface. +[classname]#Button.ClickListener# functional interface. -In the following, we handle button clicks with a listener implemented as an -anonymous class: +In the following, we assign a button click listener using a lambda expression. [source, java] ---- final Button button = new Button("Push it!"); -button.addClickListener(new Button.ClickListener() { - public void buttonClick(ClickEvent event) { - button.setCaption("You pushed it!"); - } -}); +button.addClickListener(event -> + button.setCaption("You pushed it!")); ---- <<figure.eventlistenerdiagram>> illustrates the case where an application-specific class inherits the [classname]#Button.ClickListener# interface to be able to listen for button click events. The application must instantiate the listener class and register it with -[methodname]#addClickListener()#. It can be an anonymous class, such as the one -above. When an event occurs, an event object is instantiated, in this case a +[methodname]#addClickListener()#. When an event occurs, an event object is instantiated, in this case a [classname]#Button.ClickEvent#. The event object knows the related UI component, in this case the [classname]#Button#. @@ -61,19 +56,4 @@ in this case the [classname]#Button#. .Class Diagram of a Button Click Listener image::img/events-classdiagram-hi.png[width=80%, scaledwidth=100%] -In Java 8, you can implement such functional interfaces with a lambda expression: - -[source, java] ----- -Button button = new Button("Push it!"); - -button.addClickListener(event -> - button.setCaption("You pushed it!")); ----- - -In the ancient times of C programming, __callback functions__ filled largely the -same need as listeners do now. In object-oriented languages, we usually only -have classes and methods, not functions, so the application has to give a class -interface instead of a callback function pointer to the framework. - <<dummy/../../../framework/application/application-events#application.events,"Handling Events with Listeners">> goes into details of handling events in practice. |