Adding XP Visual Style Support to OWNERDRAW Controls Using HTHEME Wrapper

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Introduction

This is a wrapper class for the HTHEME handle used in connection with the Visual Styles API available in Windows XP. This article and the code provided is heavily based on Add XP Visual Style Support in OWNERDRAW Controls by David Yuheng Zhao. To understand this article and the code provided, I strongly recommend that you read that article.

The class provided is based on the CVisualStylesXP class described in the previously mentioned article, indeed several portions of the code are copied directly, but some major conceptual changes have been made. Instead of the handle to the uxtheme.dll being a normal member of the CVisualStylesXP class, is has been made static in CXPTheme, resulting in a single load per application. Also, the function pointers returned by GetProcAddress are cached in static function pointers, which are then used in subsequent calls. In the situation where the dll is not available, the addresses of special failure member methods providing reasonable responses, are assigned to these static function pointers instead. This results in a highly optimized execution.

A more significant difference for the users of this class is the fact that CXPTheme wraps the HTHEME handle. This provides a more object-oriented approach to using the API. Unless specifically needed, the user never interacts directly with the HTHEME handle. Instead the handle is kept in a member variable and internally applied where necessary. The handle is closed in the class destructor. The class provides several constructors and overloaded operators for ease of use.

The API functions not directly related to a HTHEME are created as static member methods, not requiring an instance of the class. In addition, the static member method IsAvailable has been added for a specific check on whether the current platform supports theming. In most cases it will suffice to use the IsAppThemed API function because the corresponding special failure method will return FALSE on platforms which do not provide theming, signalling "old-style" drawing.

How to use

The class is very easy to use. First you need to include the header, preferably in stdafx.h and add the CPP file in the project.

#include "XPTheme.h"

Then you can either create a local CXPTheme variable where needed, or add it as a class member of the control.

CXPTheme theme(GetSafeHwnd(), L"TOOLBAR");
theme.DrawBackground(pDC->GetSafeHdc(), TP_BUTTON, TS_CHECKED, &rc, 0);
// the handle is closed when the variable goes out of scope.

To make your application working under all windows versions, you should do something like this:

#ifdef _XPTHEME_H_
    if (CXPTheme::IsAppThemed())
    {
        CXPTheme theme(GetSafeHwnd(), L"TOOLBAR");
        theme.DrawBackground(pDC->GetSafeHdc(), TP_BUTTON, TS_CHECKED, &rc, 0);
    }
    else
    {
#endif
        pDC->DrawEdge(....);
#ifdef _XPTHEME_H_
    }
#endif

The preferred way to use this class would probably be to make it a control member variable which is initialized in the control constructor. Once the control is deleted the CXPTheme variable will be deleted as well, and the handle closed safely. The control should handle the new WM_THEMECHANGED message, and close and reopen the theme using the Close and Open member methods. Actually the Open method could be used alone, because an open handle is closed automatically before opening a new one.

    case WM_THEMECHANGED:
        m_theme.Close();
        m_theme.Open(GetSafeHwnd(), L"TOOLBAR");
        break;

The download includes the class itself in addition to three header files taken from the Platform SDK. These are necessary to compile the code without the latest SDK. For the same reason a typedef for the WM_THEMECHANGED message has been added to the XPTheme.h file.

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