DdeCallback
The DdeCallback
function is an application-defined callback function that processes dynamic
data exchange (DDE) transactions sent to the function in response to Dynamic
Data Exchange Management Library
(DDEML) calls by other applications.
HDDEDATA CALLBACK DdeCallback(
|
UINT uType, |
// transaction type |
|
UINT uFmt, |
// clipboard data
format |
|
HCONV hconv, |
// handle to the
conversation |
|
HSZ hsz1, |
// handle to a
string |
|
HSZ hsz2, |
// handle to a
string |
|
HDDEDATA hdata, |
// handle to a
global memory object |
|
DWORD dwData1, |
//
transaction-specific data |
|
DWORD dwData2 |
//
transaction-specific data |
|
); |
|
Parameters
uType
Specifies the
type of the current transaction. This parameter consists of a combination of
transaction class flags and transaction type flags. The following table
describes each of the transaction classes and provides a list of the
transaction types in each class. For information about a specific transaction
type, see the individual description of that type.
|
Class |
Meaning |
|
XCLASS_BOOL |
A DDE
callback function should return TRUE or FALSE when it finishes processing a
transaction that belongs to this class. The XCLASS_BOOL transaction class
consists of the following types: |
|
|
|
|
XCLASS_DATA |
A DDE
callback function should return a DDE handle, the CBR_BLOCK return code, or
NULL when it finishes processing a transaction that belongs to this class.
The XCLASS_DATA transaction class consists of the following types: |
|
|
|
|
XCLASS_FLAGS |
A DDE
callback function should return DDE_FACK, DDE_FBUSY, or DDE_FNOTPROCESSED
when it finishes processing a transaction that belongs to this class. The
XCLASS_FLAGS transaction class consists of the following types: |
|
|
|
|
XCLASS_NOTIFICATION |
The
transaction types that belong to this class are for notification purposes
only. The return value from the callback function is ignored. The XCLASS_NOTIFICATION
transaction class consists of the following types: XTYP_ADVSTOP |
uFmt
Specifies the
format in which data is sent or received.
hconv
Identifies
the conversation associated with the current transaction.
hsz1
Identifies a
string. The meaning of this parameter depends on the type of the current
transaction. For the meaning of this parameter, see the description of the
transaction type.
hsz2
Identifies a
string. The meaning of this parameter depends on the type of the current
transaction. For the meaning of this parameter, see the description of the
transaction type.
hdata
Identifies
DDE data. The meaning of this parameter depends on the type of the current
transaction. For the meaning of this parameter, see the description of the
transaction type.
dwData1
Specifies
transaction-specific data. For the meaning of this parameter, see the
description of the transaction type.
dwData2
Specifies transaction-specific
data. For the meaning of this parameter, see the description of the transaction
type.
Return Values
The return
value depends on the transaction class. For more information about the return
values, see descriptions of the individual transaction types.
Remarks
The callback
function is called asynchronously for transactions that do not involve the
creation or termination of conversations. An application that does not frequently
accept incoming messages will have reduced DDE performance because the DDEML
uses messages to initiate transactions.
An
application must register the callback function by specifying a pointer to the
function in a call to the DdeInitialize function.
DdeCallback is a placeholder for the application-defined or library-defined
function name.
See Also