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CB_SETMINVISIBLE message
An application sends a CB_SETMINVISIBLE message to set the minimum number of visible items in the drop-down list of a combo box.
Parameters
...
Return value
If the message is successful, the return value is TRUE. Otherwise the return value is FALSE.
Remarks
When the number of items in the drop-down list is greater than the minimum, the combo box uses a scroll bar. By default, 30 is the minimum number of visible items.
This message is ignored if the combo box control has style CBS_NOINTEGRALHEIGHT.
To use CB_SETMINVISIBLE, the application must specify comctl32.dll version 6 in the manifest. For more information, see Enabling Visual Styles.