Hello Sam Tran,
Although displaying items in the AutoCompleteBox' dropdown is not supported out of the box, because by design the control returns results matching the entered text, our developers managed to come up with a workaround that would allow you to display the data the control is bound to on double click. I attached a sample runnable website, which demonstrates how this can be achieved. Please, note that the workaround involves overriding control methods. We generally advise against using such approach and it is not supported.
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