Push semi-working in v14

Flow
1

I have a strange issue where I do some work in a background thread and use a callback to update the UI. I have @Push on the root @Route component and the callback uses UI.access and finishes with a UI.push() for good measure but for some reason a Notification.show() turns up but e.g. an Label.setText doesn’t refresh.

How can the notification work but not the component update? Both are just changes to the DOM, right? Have I had too little coffee (or too much)?

2

Hmm. And now I get an “no UI instance available”. Which is strange since the update is being done within UI.access (UI instance stored away in view). However, if I refresh the browser, it works!

3

Yes, Notifications and component updates should be the same from the Push point of view. UI.push() shouldn’t be needed, either, unless you have explicitly set up manual push mode.

4

How are you getting the UI instance? Typically, it’s easiest to get it through a Component (or just a UI reference) you have passed on to the backing thread.

5

I pick up a UI.getCurrent() and store it in the view and do the UI.access through that. I’ve verified with UI.getUIId and eclipse debugger instance number that it’s the same one being used. There shouldn’t™ be any difference in passing along the actual instance all the way to the background thread vs e.g. accessing the same instance through a lambda?

6

Yes, that sounds like the right way to go.

7

And the browser refresh fixing it still sounds strange. If there would be a fundamental semantic thread-thingie it wouldn’t work

8

What if instead of storing the UI reference from UI.getCurent() in your view, you call view.getUI() instead?

9

Same thing. My view has @Push but if I put a

System.out.println(UI.getCurrent().getPushConfiguration().getPushMode()); in the view I get a

INFO [stdout]
(default task-191) DISABLED and after a browser refresh a
INFO [stdout]
(default task-191) AUTOMATIC

which is consistent with what I’m seeing

explicitly setting the PushMode to auto fixes my issues.

10

The plot thickens. If I go to my view by typing in the URL, @Push enables push but if I end up on my view through navigation, it’s disabled.

@Route("test1")
@RouteScoped
public class ViewA extends Div {

	public ViewA() {
		Button nav = new Button("navigate", e -> UI.getCurrent().navigate("test2"));
		add(nav);
	}
}

@Route("test2")
@RouteScoped
@Push
public class ViewB extends Div implements BeforeEnterObserver {

	@Override
	public void beforeEnter(BeforeEnterEvent event) {
		System.out.println(UI.getCurrent().getPushConfiguration().getPushMode());
	}

}
11

So you start on some View wihich doesn’t have @Push? Yes, that would explain why Push is not enabled.

12

Here’s a ticket that is describing the same issue, I think: https://github.com/vaadin/flow/issues/5759

13

Olli Tietäväinen:
Here’s a ticket that is describing the same issue, I think: https://github.com/vaadin/flow/issues/5759

Ah yes, must be the same issue. Fortunately there is an simple workaround