Event Handling

Question 1

Event Handling

Answer 1

Flow passes user interaction back to the server side as component events. The application can handle these events in Java code using an event handler.

Question 2

Event Listener

Answer 2

Lambda expressions are the easy way in Java to implement interfaces that only have a single method to implement, which is the case with event listeners.
Button button = new Button(“Click me!”,
event -> event.getSource().setText(“Clicked!!!”));
add(button);

Question 3

Handler Methods

Answer 3

You can also direct events to methods with method references:

class ButtonBar extends HorizontalLayout {
public ButtonBar() {
add(new Button(“OK”, this::ok));
add(new Button(“Cancel”, this::cancel));
}

public void ok(ClickEvent<Button> event) {
    event.getSource().setText("OKed!");
}

public void cancel(ClickEvent<Button> event) {
    event.getSource().setText("Canceled!");
} }

add(new ButtonBar());

Question 4

Main View

Answer 4

The main view itself doesn’t have a route, as it’s only a frame for the actual content views.
A main view uses AppLayout by extending it and setting up the elements in the constructor.

Question 5

Creating Header

Answer 5

The navigation bar of AppLayout is a horizontal element that can contain any component, such as a header or a horizontal menu.