[Qgis-developer] update QgsDataDefinedButton with QgsMapLayerComboBox

[matteo]

HI devs,

sorry to write again.. but I'm fighting (again) with Qt and QGIS widgets..

In the UI I have a simple spinbox and I'd like to add the chance for the 
user to use the data defined properties to update the value in the spinbox.

Unfortunately I'm not able to update the QgsMapLayerComboBox widget to 
the QgsDataDefinedButton one.

With a QgsFieldComboBox I found the easy way signal - solot:

layerChanged(QgsMapLayer*) -> setLayer(QgsMapLayer*)

that updates the QgsFieldComboBox (same thing with 
QgsFieldExpressionComboBox).

But I did not find something similar in the QgsDataDefinedButton API.

Am I missing something?

Thanks to all

Cheers

Matteo