Preset a sap.m.Select by a property of a SimpleForm

Hi,

I have a Form like that

<form:SimpleForm id="SupplierForm" minWidth="1024">

    <core:Title text="Betriebsdaten" />

        <Text id ="IDAnlkl" text="{LOSKLASSEN_ID}" />

    <Label text="Anlagenklasse" />

    <Text id = "IDAnlbez" text="{LOSKLASSEN_BEZ}" />

    <Label text="Los ID" />

    <Text id = "IDLos" text="{LOS_ID}" />

</form:SimpleForm>

And I have a sap.m.Select like that.

          <Select id="selAnlagen" items="{/Anlagenklasse}" change="handleAnlagenSelect" tooltip="{i18n>Anlagenklasse}">

                                     <core:ListItem key="{ID}" text="{LOSNAME}" />

            </Select>

So I want to preset set the  Key of the select.

I know how to do set by:

this.byId("selAnlagen").setSelectedKey(<value>);

BUT

How can I get the content of LOSKLASSEN_ID from the Form to preset the <value>

Thank you!