ドロップダウンのリスト部分を強制的に閉じます。
ドロップダウン (PRIM_MD.Dropdown) のメンバ
The CloseDropDown method provides programmatic control over the drop down list portion of the drop down.
This is useful when using the drop down as a means of data entry and you wish to open and close the drop down to show previously entered values.