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How to Process the DTN_FORMATQUERY Notification

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This topic demonstrates how to process a Format Query notification that is sent by the date and time picker (DTP) control.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

A DTP control sends a DTN_FORMATQUERY notification code to request information about the maximum possible size of a callback field within the control. Your application must handle this message to ensure that all fields are displayed properly.

The following C++ code example is an application-defined function that processes the DTN_FORMATQUERY notification code by calculating the width of the widest possible string for a given callback field.

Security Warning: Using lstrcmp incorrectly can compromise the security of your application. For example, before calling lstrcmp in the following code example you should make sure the two strings are null-terminated. You should review Security Considerations: Microsoft Windows Controls before continuing.

//  DoFormatQuery processes DTN_FORMATQUERY messages to ensure that the
//  DTP control displays callback fields properly.
//

void WINAPI DoFormatQuery(
 HWND hwndDP, 
 LPNMDATETIMEFORMATQUERY lpDTFQuery)
{
    HDC hdc;
    HFONT hFont, hOrigFont;

    //  Prepare the device context for GetTextExtentPoint32 call.
    hdc = GetDC(hwndDP);

    hFont = (HFONT) SendMessage(hwndDP, WM_GETFONT, 0L, 0L); 

    if(!hFont)
        hFont = (HFONT)GetStockObject(DEFAULT_GUI_FONT);

    hOrigFont = (HFONT) SelectObject(hdc, hFont);

    // Check to see if this is the callback segment desired. If so,
    // use the longest text segment to determine the maximum 
    // width of the callback field, and then place the information into 
    // the NMDATETIMEFORMATQUERY structure.
    if(!lstrcmp(L"XX",lpDTFQuery->pszFormat))
        GetTextExtentPoint32 (hdc,
                          L"366",  // widest date string
                          3,
                          &lpDTFQuery->szMax);

    // Reset the font in the device context; then release the context.
    SelectObject(hdc,hOrigFont);
    ReleaseDC(hwndDP, hdc);
}

Using Date and Time Picker Controls

Date and Time Picker Control Reference

Date and Time Picker