Adding Java tags/attributes for Vaadin-Form-Item causes exception

Adding a tag/java attribute for a Vaadin-Form-Item in the Bakery-App causes a exception to be thrown:

Constructor threw exception; nested exception is java.lang.IllegalArgumentException: A component specified to use a confirm-dialog element cannot use an element with tag name vaadin-form-item

Step to reproduce:

• Edit the order-details.html form
• Find the first vaadin-form-item (the one for due-date) and give it an ID (e.g. myformitem) and check the Java checkbox.
• Start app and navigate to storefront and the exception will occur.

Not sure if this is a flow issue or bakery-app issue, however it also occurs in our own app which uses several patterns from bakery-app.,

Seen in Flow 10.0.1

Full stack trace.txt

[Legioth]

This is actually caused by a bug in Designer which makes it to use the wrong types for the @Id instance field that it creates in the Java code. That issue is tracked in https://github.com/vaadin/designer/issues/1807.

It might be possible to fix the problem by manually changing the @Id instance field to have the right type, e.g. FormItem in the example you’re describing.

[Legioth]

That new error message is more helpful. The problem is that FormItem is incompatible with @Id because it doesn’t have a no-arg constructor. I created https://github.com/vaadin/vaadin-form-layout-flow/issues/53 to track this issue since this ticket is full of debugging information that turned out to not be directly relevant.

You should be able to work around the problem for now by creating your own simple MyFormItem extends FormItem class that defines a no-args constructor, and then changing your @Id definition to use that class instead.