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How to Support Callback Items

This topic demonstrates how to provide support for callback items.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

If your application is going to use callback items in a ComboBoxEx control, it must be prepared to handle the CBEN_GETDISPINFO notification code. A ComboBoxEx control sends this notification whenever it needs the owner to provide specific item information. For more information about callback items, see Callback Items.

The following application-defined function processes CBEN_GETDISPINFO by providing attributes for a given item. Note that it sets the mask member of the incoming COMBOBOXEXITEM structure to CBEIF_DI_SETITEM. Setting mask to this value makes the control retain the item information so that it will not need to request the information again.

Complete example

// DoItemCallback - Processes CBEN_GETDISPINFO by providing item
// attributes for a given callback item.

void WINAPI DoItemCallback(PNMCOMBOBOXEX pNMCBex)
{
    DWORD dwMask = pNMCBex->ceItem.mask;

    if(dwMask & CBEIF_TEXT)
    {
            // Insert code to provide item text.
    }

    if(dwMask & CBEIF_IMAGE) 
    {
        // Insert code to provide an item image index.
    }

    // Insert code to provide other callback information as desired.

    // Make the ComboBoxEx control hold onto the item information.
    pNMCBex->ceItem.mask = CBEIF_DI_SETITEM;
}

About ComboBoxEx Controls

ComboBoxEx Control Reference

Using ComboBoxEx Controls

ComboBoxEx