default sap combox box

Hi,

I am creating combo box with list items and list items are bound to a model for list item key and text are from model.

now when I display the combo box it is shown with no value, I want to default it to some value based on key from the model.

I tried setSelectedKey and setSelectedItemId both seems not working or I missed something.

how can I default the value in this case?

here I am using standard code which is attached with this.