sap.m.select selectedKey not working

Hi together,

I try to set up a form with a select box to select out of units but I just cannot figure out how to preselect a value.

here is the xmlview excerpt:

<Select
 id="idSelectCategory"
 items="{path:'ToAcceptedUnits'}"
 selectedKey="BAR"
 selectedItemId="BAR" 
 autoAdjustWidth="false"><core:Item   text="{Unit}"  key="{Unit}"/></Select>

Later I need to exchange the selectedKey value with a dynamic value of the current "parent" databinding like

selectedKey="{InputInfo/Unit}" but even with a fix value its not working.

Any hints?

Br

Sebastian