SearchableComboBox is an enhanced version of the standard ComboBox control, providing users with additional features that significantly improve its utility in modern applications. This control is designed to address common use cases where a regular ComboBox may fall short.

1. Search Functionality: As the name suggests, SearchableComboBox offers an embedded search box. This search box allows users to quickly filter through the items in the dropdown, making it particularly useful for ComboBoxes with a large number of items.
2. Custom Sorting: The control supports custom sort comparers. This means you can define your own logic to sort the items in the dropdown.
3. Placeholder Watermark: A placeholder can be displayed inside the ComboBox when no item is selected, guiding the user on the expected input or simply for improved aesthetics.
4. Enhanced UI Feedback: The control provides visual feedback when no matches are found for a search term.

First, make sure to reference the namespace where the SearchableComboBox resides.

xmlns:local="clr-namespace:SearchableComboBox"

You can use the SearchableComboBox control just like you would a regular ComboBox, but with the added properties and features.

<local:SearchableComboBox Placeholder="Select an item..." IsSearchEnabled="True">
    <!-- ComboBox items go here -->
</local:SearchableComboBox>

• IsSearchEnabled: A boolean property that controls whether the search functionality is enabled or not.
• Placeholder: A string property to set the watermark text when no item is selected.
• CustomSort: An IComparer property to provide custom sorting logic for the items in the dropdown.
• SearchTerm: A string property that reflects the current search term. This can be bound to if necessary.

• The control uses a DebounceTimer to ensure that filtering isn't too aggressive. This means there's a slight delay from when a user stops typing to when the filter is applied. This delay is set to 300 milliseconds by default.
• The control reverts the selection to the last selected item if a user's search yields no results.
• Debug lines are present in the code (controlled by the debug flag) for developers to understand the control's flow and operations. These can be removed or toggled off in production.