Handling more complex forms - forms

Question

In my current project I have to deal with more complex forms. Fields (i'll name them 'A' and 'B') are automatically filled if a specific field (i'll name that one 'C') received user input. But also if the user inputs data into field A, the fields B and C are automatically filled out.
(This is only a simple example, the current logic is a bit more complicated)
What I have to take care of is that no cycles happen (C -> A -> C -> A -> ...). So I need to now if the current value change was due to user input or another field that had received input and then triggered the value change of the current field. And I also need to now in the second case which field exactly triggered the value change because then I must trigger other specific actions corresponding from who/what triggered that value change.
Is there a general approach in Vaadin to deal with this kind of form
structure? The problem at the moment is that I simply don't now who
or what triggered what ValueChangeEvent.
Are there frameworks to deal with this or am I overlooking an existing Vaadin pattern?

Answer 1

Handling of valueChange events in Vaadin is a bit of pain, since it always fires, no matter if the user has changed something, or the application has used setValue(....) on the component.
The only solution for this is to remember when you do a setValue(....) in your application and then disable the trigger code in the other components.
For example in this case (endless loop):
field1.addValueChangeListener( field2.setValue('Updated by field1');
field2.addValueChangeListener( field1.setValue('Updated by field2');
Change it that way:
boolean inTrigger= false;
field1.addValueChangeListener(
{
if (!inTrigger)
{
inTrigger= true;
field2.setValue('Updated by field1');
inTrigger= false;
}
});
field2.addValueChangeListener(
{
if (!inTrigger)
{
inTrigger= true;
field1.setValue('Updated by field2');
inTrigger= false;
}
});
That way you can prevent update loops and let execute your code exactly once.