Combining single- and multi- select drop-down in one form. How to dismiss the drop-down?

Question

How to dismiss the drop-down in single-select and multi-select cases?

For single-select, the obvious option is to dismiss the drop-down on selection.

For multi-select, drop-down should stay open on selection, and can be dismissed with a button, or clicking outside.

Question: Will it be confusing for people to have two models of interaction side-by-side? What is the best strategy here?

Mind that cost of error ((wrong selection) is small. Nothing is saved, or processed, or launched into the space when option is selected.

Examples from the web are welcome in the comments section.

Answer 1

One potential way to have a single button to confirm the selection for both single and multiple selection dropdowns is to make "All" an option in the multiple selection dropdown.

You can position the "All" option first, and preserve the selections that the user makes if they uncheck the "All" option, or you can simply clear all selections if you uncheck the "All" option.

That way the user will make one or more selections from the list, and then click on a single Confirm button like the single selection dropdown.

There are probably other ways to implement this but you should check to see that it makes sense to apply this design pattern to the rest of the interface.