ComboBox Style - AdarshRise/HandyControl GitHub Wiki

This just replaces the standard ComboBox when you drop in the library, nothing fancy to activate it.

<ComboBox/>

To use Attached Properties, you should set Style

<ComboBox Style="{StaticResource ComboBoxExtend}"/>

if you want to use watermark or you want to show a message that user must select combobox, you should use InfoElement Attached Property, For more information about InfoElement, see here

<ComboBox hc:InfoElement.Placeholder="Please Select Content}" hc:InfoElement.Title="Groups" Style="{StaticResource ComboBoxExtend}" hc:InfoElement.Necessary="True"/>