CListBox with disabled items

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Introduction

From time to time, I have needed to have a listbox with fixed contents but with some of the items disabled. I have tried to locate such a class but never succeeded. Therefore I decided to create the class on my own.

Class CExtendedListBox

The source files of the class are available for download at the top of this article. To use the class, you simply #include "ExtendedListBox.h" and use CExtendedListBox instead of CListBox in your CDialog-derived class. (The class was not tested with Create() construction; it has been tested with DDX_Control() construction, and quite surely it will work fine with SubclassWindow().)

The class behaviour is customizable by overriding the virtual method:

virtual BOOL IsItemEnabled(UINT) const;

This method takes the item number as argument (the code should explicitely check whether the argument is out-of-bounds) and returns TRUE/FALSE. The default implementation uses the least significant bit of item data for this logic. (It's easy to see that LSB is available for pointer data, since the pointers to structures are DWORD-aligned; for integer data, you can do data_to_store=(data<<1)|is_enabled and data=stored_data>>1 to store and restore the data for the element.) By overriding the method, you can alter the behaviour (and even make it selection-dependent!).

The code works for all types of listbox selection.

The code makes no attempt to disable the selection itself. It only draws the disabled item as disabled. It's up to the programmer to handle cases when disabled item is selected.

Comments are welcome.