Switch between drop-list and drop-down mode

Environment: VC6, NT4 SP3.

switch_list.jpg (5874 bytes)

switch_drop.jpg (4847 bytes)

After reading the article written by

Robert Cremer

, I realized that his
version doesn’t correctly draw the blue selection rectangle around the selected
item within the combo box. Therefore, I took a different tack in the designing of my version of a class that allows you to programmatically switch a combo box between “drop-list” and “drop-down” mode.

To do this, I create an edit control that simulates the child edit of a
real drop-down combo box. The included files have one CComboBox derived class with overrides on OnDropDown and OnCloseUp, and one CEdit derived class that takes care
of the up/down arrows used no navigate in the combobox.

The only (let’s say) tricky parts are:

  • Making the edit selectable by mouse. I used ::SetWindowPos to put in in the front of the combo in the Z-order
  • Making the combo selectable/not selectable by TAB. ModifyStyle(WS_TABSTOP,0) to remove, ModifyStyle(0,WS_TABSTOP) to add the combo to the tab order list.

Usage

In order to use this class, simply follow these steps:

  • In your dialog, add a drop-list combobox
  • Add a member variable to the dialog of the type CComboBox
  • Modify the dialog’s header file so that instead of the newly created
    combo box variable being declared as a CComboBox, it is declared as a CFineCombo.
  • Now, update your dialog’s code to include calls to
    SwitchToDrop(TRUE) (switches to drop-down) or SwitchToDrop(FALSE) (switches
    to drop-list) where appropriate.
  • Delete the ClassWizard (.clw) file.
  • Rebuild the ClassWizard file so that it contains the newly added CFineCombo class.

Downloads

Download demo project – 20 Kb
Download source – 3 Kb

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