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CWindowImpl Class

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Provides methods for creating or subclassing a window.

Important

This class and its members cannot be used in applications that execute in the Windows Runtime.

Syntax

template <class T, class TBase = CWindow, class TWinTraits = CControlWinTraits>
class ATL_NO_VTABLE CWindowImpl : public CWindowImplBaseT<TBase, TWinTraits>

Parameters

T
Your new class, derived from CWindowImpl.

TBase
The base class of your class. By default, the base class is CWindow.

TWinTraits
A traits class that defines styles for your window. The default is CControlWinTraits.

Members

Public Methods

Name Description
CWindowImpl::Create Creates a window.

CWindowImplBaseT Methods

Name Description
DefWindowProc Provides default message processing.
GetCurrentMessage Returns the current message.
GetWindowProc Returns the current window procedure.
OnFinalMessage Called after the last message is received (typically WM_NCDESTROY).
SubclassWindow Subclasses a window.
UnsubclassWindow Restores a previously subclassed window.

Static Methods

Name Description
GetWndClassInfo Returns a static instance of CWndClassInfo, which manages the window class information.
WindowProc Processes messages sent to the window.

Data Members

Name Description
m_pfnSuperWindowProc Points to the window class's original window procedure.

Remarks

You can use CWindowImpl to create a window or subclass an existing window. the CWindowImpl window procedure uses a message map to direct messages to the appropriate handlers.

CWindowImpl::Create creates a window based on the window class information that's managed by CWndClassInfo. CWindowImpl contains the DECLARE_WND_CLASS macro, which means CWndClassInfo registers a new window class. If you want to superclass an existing window class, derive your class from CWindowImpl and include the DECLARE_WND_SUPERCLASS macro. In this case, CWndClassInfo registers a window class that's based on an existing class but uses CWindowImpl::WindowProc. For example:

class ATL_NO_VTABLE CMyWindow :
   OtherInheritedClasses
   public CComControl<CMyWindow>
          // CComControl derives from CWindowImpl
{
public:
   // 1. The NULL parameter means ATL will generate a
   //    name for the superclass
   // 2. The "EDIT" parameter means the superclass is
   //    based on the standard Windows Edit box
   DECLARE_WND_SUPERCLASS(NULL, _T("EDIT"))

   // Remainder of class declaration omitted

Note

Because CWndClassInfo manages the information for just one window class, each window created through an instance of CWindowImpl is based on the same window class.

CWindowImpl also supports window subclassing. The SubclassWindow method attaches an existing window to the CWindowImpl object and changes the window procedure to CWindowImpl::WindowProc. Each instance of CWindowImpl can subclass a different window.

Note

For any given CWindowImpl object, call either Create or SubclassWindow. Don't invoke both methods on the same object.

In addition to CWindowImpl, ATL provides CContainedWindow to create a window that's contained in another object.

The base class destructor (~ CWindowImplRoot) ensures that the window is gone before the object is destroyed.

CWindowImpl derives from CWindowImplBaseT, which derives from CWindowImplRoot, which derives from TBase and CMessageMap.

For more information about See
Creating controls ATL Tutorial
Using windows in ATL ATL Window Classes
ATL Project Wizard Creating an ATL Project

Inheritance Hierarchy

CMessageMap

TBase

CWindowImplRoot

CWindowImplBaseT

CWindowImpl

Requirements

Header: atlwin.h

CWindowImpl::Create

Creates a window based on a new window class.

HWND Create(
    HWND hWndParent,
    _U_RECT rect = NULL,
    LPCTSTR szWindowName = NULL,
    DWORD dwStyle = 0,
    DWORD dwExStyle = 0,
    _U_MENUorID MenuOrID = 0U,
    LPVOID lpCreateParam = NULL);

Parameters

hWndParent
[in] The handle to the parent or owner window.

rect
[in] A RECT structure specifying the position of the window. The RECT can be passed by pointer or by reference.

szWindowName
[in] Specifies the name of the window. The default value is NULL.

dwStyle
[in] The style of the window. This value is combined with the style provided by the traits class for the window. The default value gives the traits class full control over the style. For a list of possible values, see CreateWindow in the Windows SDK.

dwExStyle
[in] The extended window style. This value is combined with the style provided by the traits class for the window. The default value gives the traits class full control over the style. For a list of possible values, see CreateWindowEx in the Windows SDK.

MenuOrID
[in] For a child window, the window identifier. For a top-level window, a menu handle for the window. The default value is 0U.

lpCreateParam
[in] A pointer to window-creation data. For a full description, see the description for the final parameter to CreateWindowEx.

Return Value

If successful, the handle to the newly created window. Otherwise, NULL.

Remarks

Create first registers the window class if it has not yet been registered. The newly created window is automatically attached to the CWindowImpl object.

Note

Do not call Create if you have already called SubclassWindow.

To use a window class that is based on an existing window class, derive your class from CWindowImpl and include the DECLARE_WND_SUPERCLASS macro. The existing window class's window procedure is saved in m_pfnSuperWindowProc. For more information, see the CWindowImpl overview.

Note

If 0 is used as the value for the MenuOrID parameter, it must be specified as 0U (the default value) to avoid a compiler error.

CWindowImpl::DefWindowProc

Called by WindowProc to process messages not handled by the message map.

LRESULT DefWindowProc(
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam);

LRESULT DefWindowProc();

Parameters

uMsg
[in] The message sent to the window.

wParam
[in] Additional message-specific information.

lParam
[in] Additional message-specific information.

Return Value

The result of the message processing.

Remarks

By default, DefWindowProc calls the CallWindowProc Win32 function to send the message information to the window procedure specified in m_pfnSuperWindowProc.

The function with no parameters automatically retrieves the needed parameters from the current message.

CWindowImpl::GetCurrentMessage

Returns the current message, packaged in the MSG structure.

const MSG* GetCurrentMessage();

Return Value

The current message.

CWindowImpl::GetWindowProc

Returns WindowProc, the current window procedure.

virtual WNDPROC GetWindowProc();

Return Value

The current window procedure.

Remarks

Override this method to replace the window procedure with your own.

CWindowImpl::GetWndClassInfo

Called by Create to access the window class information.

static CWndClassInfo& GetWndClassInfo();

Return Value

A static instance of CWndClassInfo.

Remarks

By default, CWindowImpl obtains this method through the DECLARE_WND_CLASS macro, which specifies a new window class.

To superclass an existing window class, derive your class from CWindowImpl and include the DECLARE_WND_SUPERCLASS macro to override GetWndClassInfo. For more information, see the CWindowImpl overview.

Besides using the DECLARE_WND_CLASS and DECLARE_WND_SUPERCLASS macros, you can override GetWndClassInfo with your own implementation.

CWindowImpl::m_pfnSuperWindowProc

Depending on the window, points to one of the following window procedures.

WNDPROC m_pfnSuperWindowProc;

Remarks

Type of window Window procedure
A window based on a new window class, specified through the DECLARE_WND_CLASS macro. The DefWindowProc Win32 function.
A window based on a window class that modifies an existing class, specified through the DECLARE_WND_SUPERCLASS macro. The existing window class's window procedure.
A subclassed window. The subclassed window's original window procedure.

CWindowImpl::DefWindowProc sends message information to the window procedure saved in m_pfnSuperWindowProc.

CWindowImpl::OnFinalMessage

Called after receiving the last message (typically WM_NCDESTROY).

virtual void OnFinalMessage(HWND hWnd);

Parameters

hWnd
[in] A handle to the window being destroyed.

Remarks

The default implementation of OnFinalMessage does nothing, but you can override this function to handle cleanup before destroying a window. If you want to automatically delete your object upon the window destruction, you can call delete this; in this function.

CWindowImpl::SubclassWindow

Subclasses the window identified by hWnd and attaches it to the CWindowImpl object.

BOOL SubclassWindow(HWND hWnd);

Parameters

hWnd
[in] The handle to the window being subclassed.

Return Value

TRUE if the window is successfully subclassed; otherwise, FALSE.

Remarks

The subclassed window now uses CWindowImpl::WindowProc. The original window procedure is saved in m_pfnSuperWindowProc.

Note

Do not call SubclassWindow if you have already called Create.

CWindowImpl::UnsubclassWindow

Detaches the subclassed window from the CWindowImpl object and restores the original window procedure, saved in m_pfnSuperWindowProc.

HWND UnsubclassWindow();

Return Value

The handle to the window previously subclassed.

CWindowImpl::WindowProc

This static function implements the window procedure.

static LRESULT CALLBACK WindowProc(
    HWND hWnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam);

Parameters

hWnd
[in] The handle to the window.

uMsg
[in] The message sent to the window.

wParam
[in] Additional message-specific information.

lParam
[in] Additional message-specific information.

Return Value

The result of the message processing.

Remarks

WindowProc uses the default message map (declared with BEGIN_MSG_MAP) to direct messages to the appropriate handlers. If necessary, WindowProc calls DefWindowProc for additional message processing. If the final message is not handled, WindowProc does the following:

  • Performs unsubclassing if the window was unsubclassed.

  • Clears m_hWnd.

  • Calls OnFinalMessage before the window is destroyed.

You can override WindowProc to provide a different mechanism for handling messages.

See also

BEGIN_MSG_MAP
CComControl Class
Class Overview