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[Databinding] Validate that item only appears once in IObservableList [message #517472]

Sun, 28 February 2010 08:00

Philipp Kursawe
Messages: 135
Registered: July 2009

Senior Member

Hello,

I have a table editor that allows the creation of new entries.
There should be only one entry in the table with a specific name.
The table cell editor should therefor prevent the user from changing the
name to a value already existing in the table (list).

What kind of binding would do that automatically?

Thanks,
Phil

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Re: [Databinding] Validate that item only appears once in IObservableList [message #517707 is a reply to message #517472]

Mon, 01 March 2010 13:49

Eric Rizzo
Messages: 2011
Registered: July 2009

Senior Member

On 2/28/10 8:00 AM, Philipp Kursawe wrote:
> Hello,
>
> I have a table editor that allows the creation of new entries.
> There should be only one entry in the table with a specific name.
> The table cell editor should therefor prevent the user from changing the
> name to a value already existing in the table (list).
>
> What kind of binding would do that automatically?

One idea is to wrap the observable in an
org.eclipse.core.databinding.observable.value.IVetoableValue (see
org.eclipse.core.databinding.observable.value.DecoratingVeto ableValue)

Another idea is to provide a custom UpdateValueStrategy to the binding.

Hope this helps,
Eric

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Re: [Databinding] Validate that item only appears once in IObservableList [message #518431 is a reply to message #517472]

Thu, 04 March 2010 01:07

Matthew Hall
Messages: 368
Registered: July 2009

Senior Member

Philipp Kursawe wrote:
> Hello,
>
> I have a table editor that allows the creation of new entries.
> There should be only one entry in the table with a specific name.
> The table cell editor should therefor prevent the user from changing the
> name to a value already existing in the table (list).
>
> What kind of binding would do that automatically?
>
> Thanks,
> Phil

You could allow the change in the UI but prevent invalid changes from
propagating to the model using a MultiValidator:

IObservableList items = ...

final IObservableList itemNames =
BeanProperties.value("name").observeDetail(items);

MultiValidator uniqueNamesValidator = new MultiValidator() {
protected IStatus validate() {
Set names = new HashSet();
for (Iterator it = itemNames.iterator(); it.hasNext();) {
String name = (String) it.next();
if (!names.add(name) {
return ValidationStatus.error("The name \""+name+
"\"" cannot appear more than once.");
}
}
}
};

bindingContext.addValidationStatusProvider(uniqueNamesValida tor);

This much will flag a validation error in your UI (assuming you have the
validation status wired up and displayed somewhere--right?).

Next you can tell uniqueNamesValidator to wrap your target observable
list in a validated wrapper. Changes to the wrapped observable will
only propagate out to the wrapper when the validator is in a passing status:

bindingContext.bindList(uniqueNamesValidator.observeValidate dList(items),
modelList);

Hope this helps,

Matthew

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