CDynamicChain Class

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This class provides methods supporting the dynamic chaining of message maps.

Syntax

class CDynamicChain

Members

Public Constructors

Public Methods

Remarks

CDynamicChain manages a collection of message maps, enabling a Windows message to be directed, at run time, to another object's message map.

To add support for dynamic chaining of message maps, do the following:

• Derive your class from CDynamicChain. In the message map, specify the CHAIN_MSG_MAP_DYNAMIC macro to chain to another object's default message map.

• Derive every class you want to chain to from CMessageMap. CMessageMap allows an object to expose its message maps to other objects.

• Call CDynamicChain::SetChainEntry to identify which object and which message map you want to chain to.

For example, suppose your class is defined as follows:

class CMyChainWnd : public CWindowImpl<CMyChainWnd>,
   public CDynamicChain
{
public:
   CMyChainWnd() {}

   BEGIN_MSG_MAP(CMyChainWnd)
      MESSAGE_HANDLER(WM_PAINT, OnPaint)
      MESSAGE_HANDLER(WM_SETFOCUS, OnSetFocus)
      // dynamically chain to the default
      // message map in another object
      CHAIN_MSG_MAP_DYNAMIC(1313)
                // '1313' identifies the object
                // and the message map that will be
                // chained to. '1313' is defined
                // through the SetChainEntry method
   END_MSG_MAP()

   LRESULT OnPaint(UINT /*nMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, 
      BOOL& /*bHandled*/)
   {
      // Do some painting code
      return 0;
   }

   LRESULT OnSetFocus(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, 
      BOOL& /*bHandled*/)
   { 
      return 0;
   }
};

The client then calls CMyWindow::SetChainEntry:

   myCtl.SetChainEntry(1313, &chainedObj);

where chainedObj is the chained object and is an instance of a class derived from CMessageMap. Now, if myCtl receives a message that is not handled by OnPaint or OnSetFocus, the window procedure directs the message to chainedObj's default message map.

For more information about message map chaining, see Message Maps in the article "ATL Window Classes."

Requirements

Header: atlwin.h

CDynamicChain::CallChain

Directs the Windows message to another object's message map.

BOOL CallChain(  
    DWORD dwChainID,
    HWND hWnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam,
    LRESULT& lResult);

Parameters

dwChainID
[in] The unique identifier associated with the chained object and its message map.

hWnd
[in] The handle to the window receiving the message.

uMsg
[in] The message sent to the window.

wParam
[in] Additional message-specific information.

lParam
[in] Additional message-specific information.

lResult
[out] The result of the message processing.

Return Value

TRUE if the message is fully processed; otherwise, FALSE.

Remarks

For the window procedure to invoke CallChain, you must specify the CHAIN_MSG_MAP_DYNAMIC macro in your message map. For an example, see the CDynamicChain overview.

CallChain requires a previous call to SetChainEntry to associate the dwChainID value with an object and its message map.

CDynamicChain::CDynamicChain

The constructor.

CDynamicChain();

CDynamicChain::~CDynamicChain

The destructor.

~CDynamicChain();

Remarks

Frees all allocated resources.

CDynamicChain::RemoveChainEntry

Removes the specified message map from the collection.

BOOL RemoveChainEntry(DWORD dwChainID);

Parameters

dwChainID
[in] The unique identifier associated with the chained object and its message map. You originally define this value through a call to SetChainEntry.

Return Value

TRUE if the message map is successfully removed from the collection. Otherwise, FALSE.

CDynamicChain::SetChainEntry

Adds the specified message map to the collection.

BOOL SetChainEntry(  
    DWORD dwChainID,
    CMessageMap* pObject,
    DWORD dwMsgMapID = 0);

Parameters

dwChainID
[in] The unique identifier associated with the chained object and its message map.

pObject
[in] A pointer to the chained object declaring the message map. This object must derive from CMessageMap.

dwMsgMapID
[in] The identifier of the message map in the chained object. The default value is 0, which identifies the default message map declared with BEGIN_MSG_MAP. To specify an alternate message map declared with ALT_MSG_MAP(msgMapID), pass msgMapID.

Return Value

TRUE if the message map is successfully added to the collection. Otherwise, FALSE.

Remarks

If the dwChainID value already exists in the collection, its associated object and message map are replaced by pObject and dwMsgMapID, respectively. Otherwise, a new entry is added.

See Also

CWindowImpl Class
Class Overview