WM_DDE_DATA Overview  Group

A DDE server application posts a WM_DDE_DATA message to a DDE client application to pass a data item to the client or to notify the client of the availability of a data item.

WM_DDE_DATA 

wParam = (WPARAM) hwnd;         // handle of posting application 

lParam = (LPARAM) lPackedVal;   // packed DDEDATA and item atom 

 

Parameters

hwnd

Value of wParam. Identifies the server window posting the message.

lPackedVal

Value of lParam. The component parameters that are packed into lPackedVal are extracted by calling the UnpackDDElParam function. The low-order word is hData or NULL. The high-order word is aItem.

Parameter	Description
hData	Identifies a global memory object containing a DDEDATA structure with the data and additional information. The handle should be set to NULL if the server is notifying the client that the data-item value has changed during a warm data link. A warm link is established by the client sending a WM_DDE_ADVISE message with the fDeferUpd bit set.
aItem	Contains an atom that identifies the data item for which the data or notification is sent.

Remarks

Posting 

The server application posts the WM_DDE_DATA message by calling the PostMessage function, not the SendMessage function.

The server application allocates hData by calling the GlobalAlloc function with the GMEM_DDESHARE option. It allocates aItem by calling the GlobalAddAtom function.

The server must create or reuse the WM_DDE_DATA lPackedVal parameter by calling the PackDDElParam function or the ReuseDDElParam function with hData supplied as the low-order word and aItem supplied as the high-order word.

If the receiving (client) application responds with a negative WM_DDE_ACK message, the posting (server) application must delete the hData object; otherwise, the client must delete the hData object after extracting its contents by calling the UnpackDDElParam function.

If the server application sets the fRelease member of the DDEDATA structure to FALSE, the server is responsible for deleting hData upon receiving either a positive or negative acknowledgement.

The server application should not set both the fAckReq and fRelease members of the DDEDATA structure to FALSE. If both members are set to FALSE, it is impossible for the server to determine when to delete hData.

Receiving 

If fAckReq is TRUE, the client application should post the WM_DDE_ACK message to respond positively or negatively. When posting WM_DDE_ACK, the client can either reuse the aItem atom, or it can delete it and create a new one.

The client must create or reuse the WM_DDE_ACK lPackedVal parameter by calling the PackDDElParam function or the ReuseDDElParam function with wStatus supplied as the low-order word and aItem supplied as the high-order word.

If fAckReq is FALSE, the client application should delete the aItem atom.

If the posting (server) application specified hData as NULL, the receiving (client) application can request the server to send the data by posting a WM_DDE_REQUEST message.

After processing a WM_DDE_DATA message in which hData is not NULL, the client should free hData, unless one of the following conditions is true:

• The fRelease member is FALSE.

• The fRelease member is TRUE, but the client application responds with a negative WM_DDE_ACK message.

See Also

DDEDATA, FreeDDElParam, GlobalAddAtom, GlobalAlloc, PackDDElParam, PostMessage, ReuseDDElParam, SendMessage, UnpackDDElParam, WM_DDE_ACK, WM_DDE_ADVISE, WM_DDE_POKE, WM_DDE_REQUEST