The OK push button initiates the default action.
When a subdirectory is selected, the File Name field is empty. When the user clicks on the OK push button or presses the Enter key, the subdirectory is opened and the displayed values in the File list box and the Directory list box are refreshed.
When a file name is selected, selection of subdirectories is canceled and the File Name field is updated with the name of the selected file. When the user clicks on the OK push button or presses the Enter key, the file displayed in the File Name field is returned to the application for opening.