hello, i've got two comboboxes with the same content. the user should not be allowed to choose the same item twice. therefore the comboboxes' contents (= selectedindex?) should never be equal. my first attempt was to comapare the selectedindex with a datatrigger to show/hide a button: <DataTrigger Binding="{Binding ElementName=comboBox1, Path=SelectedIndex}" Value="{Binding ElementName=comboBox2, Path=SelectedIndex}"> <Setter Property="Visibility" Value="Hidden" /> </DataTrigger> it seems that it is not possible to use Value={Binding}. is there any other way (if possible without using a converter)? thanks in advance!