CustomEvent examples

[Gordan Krešić]

Are there any examples/best cases of using elemental2.dom.CustomEvent in GWT
2.9?

My primary use case is to use it as a replacement for GwtEvent in elemental2
components.

-gkresic.

[Thomas Broyer]

On Friday, August 28, 2020 at 7:29:37 PM UTC+2, Gordan Krešić wrote:

Are there any examples/best cases of using elemental2.dom.CustomEvent in GWT
2.9?

https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Creating_and_triggering_events

The second example would be coded as:

CustomEventInit<Double> eventInit = CustomEventInit.create();
eventInit.setDetail(time);
CustomEvent event = new CustomEvent("build", eventInit);

[Gordan Krešić]

On 28. 08. 2020. 23:28, Thomas Broyer wrote:
>
> https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Creating_and_triggering_events
>
> The second example would be coded as:
>
> CustomEventInit<Double>eventInit =CustomEventInit.create();
> eventInit.setDetail(time);
> CustomEventevent=newCustomEvent("build",eventInit);

With the exception of CustomEventInit not being generic, this code works,
thanks Thomas.

In an example of event to signal that particular user is saved, this is what
I got working:

Declarations:

public static final String SavedEventType = "saved";

Init:

addEventListener(SavedEventType, this::onSaved);

Dispatch:

public void save(User user) {
CustomEventInit eventInit = CustomEventInit.create();
eventInit.setDetail(user);
eventInit.setBubbles(false);
CustomEvent event = new CustomEvent(SavedEventType, eventInit);
dispatchEvent(event);
}

Listener:

public void onSaved(Event event) {
CustomEvent customEvent = (CustomEvent) event;
User user = (User) customEvent.detail;
Log.info("User is " + user.getId());
}

Looks very fragile, especially if I decide to use complex details in which
case I'll have to expose internal structure of that field.

IMHO, best solution would be to extend CustomEvent, but I didn't find a way
to do so (as least not in a way to be able to *receive* instances of that
descended class, not even using Js.uncheckedCast, which, to my understanding
of JsInterop, is not even possible), so this is best I got:

public class SavedEvent {

public static final String Type = SavedEvent.class.getName();

@JsType(isNative = true, name = "CustomEventInit", namespace =
JsPackage.GLOBAL)
public static interface Init extends CustomEventInit {

@JsOverlay
static SavedEvent.Init create() {
SavedEvent.Init init = Js.uncheckedCast(CustomEventInit.create());
init.setBubbles(false);
return init;
}

@JsOverlay
default User getUser() {
return (User) getDetail();
}

@JsOverlay
default SavedEvent.Init setUser(User user) {
setDetail(user);
return this;
}

@JsOverlay
default CustomEvent event() {
return new CustomEvent(SavedEvent.Type, this);
}

}

public interface Listener extends EventListener {
default void handleEvent(Event event) {
handleEvent(new SavedEvent(event));
}
void handleEvent(SavedEvent event);
}

public SavedEvent(Event nativeEvent) {

// add at least some safety...
if (!(nativeEvent instanceof CustomEvent) || !Type.equals(nativeEvent.type))
throw new IllegalArgumentException();

this.nativeEvent = (CustomEvent) nativeEvent;

}

public CustomEvent getNativeEvent() {
return nativeEvent;
}

public User getUser() {
return (User) nativeEvent.detail;
}

private final CustomEvent nativeEvent;

}

Which contains a lot of boilerplate wrappers, but at least now dispatchers
and listeners (which are exposed to users) looks more decent:

addEventListener(SavedEvent.Type, this::onSaved);

public void save(User user) {
dispatchEvent(SavedEvent.Init.create().setUser(user).event());
}

public void onSaved(SavedEvent event) {
Log.info("Saved user is " + event.getUser().getId());
}

Any suggestions for further simplifications when working with specialized
events?

-gkresic.