The ComboBox is designed to select a value in a set of items. For more information about its usage, see Combo box and list box Microsoft documentation.

Customize the placement of the Drop-Down (UNO-only feature)

By default, when opening a ComboBox, WinUI aligns its drop-down to keep the selected item at the same location. This means that, if the currently selected value is the last one in the list, the drop-down will appear above the ComboBox. If there isn't any selected item, the drop-down will appear centered over the ComboBox.

On Uno, you can change this behavior using DefaultDropDownPreferredPlacement or DropDownPreferredPlacement.

Change the default value for all the ComboBox in your application

The default placement for all ComboBox instances can be changed by setting the feature flag in the startup of your app (App.cs or App.xaml.cs):

Uno.UI.FeatureConfiguration.ComboBox.DefaultDropDownPreferredPlacement = DropDownPlacement.Below;

Change only for a specific ComboBox

    mc:Ignorable="d not_win">

        not_win:ComboBox.DropDownPreferredPlacement="Below" />