WM_DDE_DATA 14XLR0E

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 UnpackDDElParam51WGIV 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 DDEDATARNRBH. 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_ADVISE1FMIUGC 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 PostMessageFIXDT_ function, not the SendMessage1724MSN function.

The server application allocates hData by calling the GlobalAllocF12W9. function with the GMEM_DDESHARE option. It allocates aItem by calling the GlobalAddAtom1QH2CM4 function.

The server must create or reuse the WM_DDE_DATA lPackedVal parameter by calling the PackDDElParam1_GBV6Y function or the ReuseDDElParam14DC0A 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_ACK9K0..A 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 UnpackDDElParam51WGIV function.

If the server application sets the fRelease member of the DDEDATARNRBH. 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_ACK9K0..A 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 PackDDElParam1_GBV6Y function or the ReuseDDElParam14DC0A 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.