Instead of multi-selection combo box, I would strongly recommend to create a combo box with check box elements. This way, check states instead of selection provides better visual feedback, reduces accidental mistakes, and so on. It would be hard, for example, to implement "nothing selected" state and then see the difference between highlighting and selection, and so on. Multi-selection list box or combo box style is not quite consistent with customary UI styles.
It's easy to implement from scratch in WPF, but see, for example,
C# Corner: Multi Select ComboBox in WPF.
If you still want multiple selection as it is, you could use
ListBox instead of
ComboBox which you can combined with
TextBox in your own combined control (
UserControl or custom control). If you wanted this alternative, you could use
ListBox.SelectionMode:
ListBox.SelectionMode Property (System.Windows.Controls)[
^],
SelectionMode Enumeration (System.Windows.Controls)[
^].
But I still would strongly recommend to prefer check boxes in the list elements.
Happy New Year!
—SA
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