Most Recently Used List in a Combobox

Intro

MFC implements a convenient feature called a most recently used list, or MRU. In SDI and MDI apps generated by AppWizard, the MRU list appears on the File menu. However, another handy place where MRUs are used is in comboboxes. For example, the Start/Run dialog lists the last few programs that you've run in its combobox.

While MFC does not directly support placing an MRU in a combobox, the class CRecentFileList (which implements the File menu MRU list) provides several member functions for maintining, saving, and loading an MRU list. My CMRUComboBox class encapsulates this functionality, and adds the logic necessary to put the MRU in a combobox.

CMRUComboBox was written with MSVC 5.0 and MFC 4.2. I have tested it on Win 98 and NT 4 (ANSI and Unicode builds).

Using an MRU combobox

To use CMRUComboBox, create a combobox control with the CBS_DROPDOWN style. Including CBS_AUTOHSCROLL also is not a bad idea, since without this style, the edit portion of the combobox will not scroll, effectively limiting the amount of text that can be typed in the edit box.. Use ClassWizard to add a member variable of type CComboBox that is hooked to the combobox control. Then, go to the source and change the type of the variable to CMRUComboBox. CMRUComboBox derives from CComboBox so all the operations you normally do with CComboBoxes will still work the same; CMRUComboBox just adds new methods for managing the MRU list.

In your OnInitDialog() (or other initialization code), you will need to set up a few parameters and flags for the MRU list. At minimum, set the maximum size for the MRU list, and the location in the registry (or INI file) where the list will be saved. There are also a few flags you can optionally set, which are described in the HTML documentation that is in the ZIP file that contains the source code.

Once all that initialization is done, call LoadMRU() to read in the saved contents of the MRU list. When you want to add a string to the list, call AddToMRU(). Duplicate strings are automatically brought to the top of the list, just as in File menu MRU lists. When you want to save the contents of the MRU, call SaveMRU().

Methods List

This is a list of all the new methods available for maintaining an MRU. The full docs are included in the ZIP file that contains the source code files.

BOOL            AddToMRU ( LPCTSTR szNewItem )
void            EmptyMRU()
int             SetMaxMRUSize ( int nMaxSize )
int             GetMaxMRUSize()
void            SetMRURegKey ( LPCTSTR szRegKey )
const CString&  GetMRURegKey()
BOOL            SetMRUValueFormat ( LPCTSTR szValueFormat )
const CString&  GetMRUValueFormat()
BOOL            LoadMRU()
BOOL            SaveMRU()
void            RefreshCtrl()
BOOL            SetAutoRefreshAfterAdd ( BOOL bAutoSave )
BOOL            SetAutoSaveAfterAdd ( BOOL bAutoSave )
BOOL            SetAutoSaveOnDestroy ( BOOL bAutoSave )

Simple example

Here is a sample usage of CMRUComboBox. Suppose you have a dialog similar to the one pictured at the beginning of this article, which has a place for the user to enter a path to a file, and you want to list the last few filenames to be quickly available in the MRU list.. Once you've created a CMRUComboBox member variable in your dialog class as described above, you would do the following in your OnInitDialog() function:

    m_combo.SetMRURegKey ( _T("Location Dlg MRU") );
    m_combo.SetMRUValueFormat ( _T("File%d") );
    m_combo.SetMaxMRUSize ( 12 );
    VERIFY ( m_combo.LoadMRU() );

Then, whenever you want to add a string to the MRU, call

    m_combo.AddToMRU ( szFilename );

Notes

Unfortunately, because CRecentFileList assumes that all the strings it holds are filenames, the strings added with AddToMRU() must also be filenames. (If you want to see what happens, trace into AddToMRU() and the MFC functions that CRecentFileList calls.) If you add a plain word, it will have the current directory tacked on before it. The solution to this would be to implement a new CRecentFileList work-alike that does not make this assumption.