Interprocess communication using DDE (Dynamic Data Exchange) - Part2 [ All Languages » VB »  System] Total Hit ( 9866) Rate this article:     Poor     Excellent   Submit Your Question/Comment about this article Rating Click here to download the attached file

In our previous article Interprocess communication using DDE (Dynamic Data Exchange) - Part1 of this this series we learned about basic concept of DDE and we also saw that how to implement DDE Server using DDEML Apis. Now in this article I will show you how to implement DDE Client which can request data from DDE Server and send data to DDE Server. Steps to implement DDE Client Initialize the DDE subsystem by calling DdeInitialize. Create string handles for server/topic using DdeCreateStringHandle Call DdeConnect to connect with DDE Server which is registered only for server/topic which we used in step 2. Once you connect you can do various DDE Operations (i.e. Request Data, Execute Command, Poke Data, Start/Stop Advisory Request etc.) by calling DdeClientTransaction function. If you dont want to break DDE conversation then call DdeDisconnect and then DdeUninitialize to break down the link with DDE Server and the DDE subsystem Now lets implement DDE Client Step-By-Step Example - Create a standard exe project - Change project name to DDEClient - Add one module to the project - Add eight command button controls, 3 text box controls and one combobox control on the form1 - Add the following code in form1 Click here to copy the following block Option Explicit Dim bAdvise As Boolean Private Sub Combo1_Click()      ' Adjust button states.   Select Case Combo1.Text     Case "<None>"       Command2.Enabled = True       Command3.Enabled = False       Command4.Enabled = False       Command7.Enabled = False       Command6.Enabled = False          Case "MyAdvise"       If (bAdvise) Then         Command7.Enabled = True       Else         Command6.Enabled = True       End If       Command2.Enabled = False       Command3.Enabled = False       Command4.Enabled = False            Case "MyPoke"       Command2.Enabled = False       Command3.Enabled = True       Command4.Enabled = False       Command7.Enabled = False       Command6.Enabled = False          Case "MyRequest"       Command2.Enabled = False       Command3.Enabled = False       Command4.Enabled = True       Command7.Enabled = False       Command6.Enabled = False   End Select End Sub Private Sub Command1_Click() Dim oCtl As Control      Debug.Print "------------------- Begin DDE Test -----------------------"      g_lInstID = 0      ' Initialize the DDE subsystem. This only needs to be done once.   If DdeInitialize(g_lInstID, AddressOf DDECallback, APPCMD_CLIENTONLY Or MF_SENDMSGS Or MF_POSTMSGS, 0) Then          Debug.Print "DDE Initialize Failure."     TranslateError   Else     Debug.Print "DDE Initialize Success."      End If        ' Enable the command buttons.   For Each oCtl In Controls     If ((TypeOf oCtl Is TextBox) Or (TypeOf oCtl Is ComboBox)) And (oCtl.Enabled = False) Then       oCtl.Enabled = True     End If   Next      Command1.Enabled = False   Command5.Enabled = True   Command8.Enabled = True   Combo1.ListIndex = 0    End Sub Private Sub Command5_Click()    Dim oCtl As Control      ' Make sure we don't have any open connections.   If (g_hDDEConv <> 0) Then     DDE_Disconnect   End If      ' Tear down the initialized instance.   If g_lInstID Then          If DdeUninitialize(g_lInstID) Then       Debug.Print "DDE Uninitialize Success."     Else       Debug.Print "DDE Uninitialize Failure."       TranslateError     End If          g_lInstID = 0   End If   Debug.Print "-------------------- End DDE Test ------------------------"   ' Disable the command buttons and the text boxes.   For Each oCtl In Controls        If ((TypeOf oCtl Is CommandButton) And (oCtl.Enabled = True)) Or _       ((TypeOf oCtl Is TextBox) And (oCtl.Enabled = True)) Or _       ((TypeOf oCtl Is ComboBox) And (oCtl.Enabled = True)) Then            oCtl.Enabled = False     End If   Next   Command1.Enabled = True    End Sub Private Sub Command6_Click()   If (CheckData("Advise")) Then     DDE_StartAdvise     bAdvise = True   Else     MsgBox "Please enter the required data for the transaction."   End If End Sub Private Sub Command7_Click()   If (CheckData("Advise")) Then     DDE_StopAdvise     bAdvise = False   Else     MsgBox "Please enter the required data for the transaction."   End If End Sub Private Sub Command2_Click()    Dim lRet As Long Dim sValue As String          If (CheckData("Execute")) Then     ' Load the buffer.     sValue = Text3.Text        ' Create the string handles.     DDE_CreateStringHandles Text1.Text, Text2.Text          ' Open the conversation.     If (g_hDDEConv = 0) Then       g_hDDEConv = DDE_Connect     End If          If g_hDDEConv Then            ' Perform the transaction.       lRet = DdeClientTransaction(sValue, Len(sValue), g_hDDEConv, 0, 0, XTYP_EXECUTE, 2000, 0)            If (lRet) Then                Debug.Print "DDE Execute Success."            Else                Debug.Print "DDE Execute Failure."         TranslateError            End If            End If          ' Release the memory.     DDE_FreeStringHandles   Else     MsgBox "Please enter the required data for the transaction."   End If End Sub Private Sub Command4_Click() Dim lRet As Long Dim lSize As Long Dim sBuffer As String Dim sFinal As String        If (CheckData("Request")) Then     DDE_CreateStringHandles Text1.Text, Text2.Text, Combo1.Text          ' Open the conversation.     If (g_hDDEConv = 0) Then       g_hDDEConv = DDE_Connect     End If          If g_hDDEConv Then            ' Perform the transaction.       lRet = DdeClientTransaction(0, 0, g_hDDEConv, g_hItem, CF_TEXT, XTYP_REQUEST, 2000, 0)              If (lRet) Then                Debug.Print "DDE Request Success."                  ' Grab the data from the DDE object create during the transaction. The DDE object         ' is part of the DDE subsystem memory. Once we get what we want we need to free         ' the object. Check the Microsoft Platform SDK for more information on freeing         ' DDE global memory.                  ' The first call returns the size of the of the string. For some reason there's         ' always an extra 3 bytes attached to the end of the string. That's why I have a magic         ' number.         lSize = DdeGetData(lRet, vbNullString, 0, 0)                  ' Allocate a buffer for the return data.         sBuffer = String$(lSize, 0)                        ' Grab the data.         lSize = DdeGetData(lRet, sBuffer, Len(sBuffer), 0)            ' Print the contents of the buffer.         Text3.Text = sBuffer         Debug.Print sBuffer            ' Free the DDE subsystem resources.         DdeFreeDataHandle lRet                Else                  Debug.Print "DDE Request Failed"         TranslateError              End If            End If          DDE_FreeStringHandles   Else     MsgBox "Please enter the required data for the transaction."   End If End Sub Private Sub Command3_Click()    Dim lRet As Long Dim sValue As String          If (CheckData("Poke")) Then     ' Load the buffer.     sValue = Text3.Text          DDE_CreateStringHandles Text1.Text, Text2.Text, Combo1.Text          ' Open the conversation.     If (g_hDDEConv = 0) Then       g_hDDEConv = DDE_Connect     End If          If g_hDDEConv Then       ' Perform the transaction.       lRet = DdeClientTransaction(sValue, Len(sValue), g_hDDEConv, g_hItem, CF_TEXT, XTYP_POKE, 2000, 0)              If (lRet) Then         Debug.Print "DDE Poke Success"       Else         Debug.Print "DDE Poke Failed"         TranslateError       End If     End If          DDE_FreeStringHandles   Else     MsgBox "Please enter the required data for the transaction."   End If End Sub Private Sub Command8_Click()   ' Clear out the text boxes.   Combo1.ListIndex = 0   Text3.Text = "" End Sub Private Sub DDE_CreateStringHandles(ByRef sTheService As String, ByRef sTheTopic As String, Optional ByRef sTheItem As String = "")      ' Create the string handles for the service and topic. DDEML will not   ' allow you to use standard strings. NOTE: Make sure to release the   ' string handles once you are done with them.   g_hService = DdeCreateStringHandle(g_lInstID, sTheService, CP_WINANSI)   g_hTopic = DdeCreateStringHandle(g_lInstID, sTheTopic, CP_WINANSI)      ' Only convert the item if we were passed a string otherwise you'll get a memory   ' error.   If (sTheItem <> "") Then          g_hItem = DdeCreateStringHandle(g_lInstID, Combo1.Text, CP_WINANSI)      End If End Sub Private Sub DDE_FreeStringHandles()   ' Release our string handles.   If (g_hService <> 0) Then     DdeFreeStringHandle g_lInstID, g_hService     DdeFreeStringHandle g_lInstID, g_hTopic   End If      If (g_hItem <> 0) Then     DdeFreeStringHandle g_lInstID, g_hItem   End If      g_hService = 0   g_hTopic = 0   g_hItem = 0 End Sub Private Function DDE_Connect() As Long Dim udtConvCont As CONVCONTEXT Dim hDDEConv As Long        ' Set up the conversation context structure.   udtConvCont.iCodePage = CP_WINANSI   udtConvCont.cb = Len(udtConvCont)      hDDEConv = 0      ' Open the connection to the service.   hDDEConv = DdeConnect(g_lInstID, g_hService, g_hTopic, udtConvCont)      ' Do we have a connection?   If hDDEConv Then     Debug.Print "DDE Connection Success."   Else     Debug.Print "DDE Connection Failure."     TranslateError   End If      DDE_Connect = hDDEConv    End Function Private Sub DDE_Disconnect()          ' Disconnect the DDE conversation.   If g_hDDEConv Then          If DdeDisconnect(g_hDDEConv) Then       Debug.Print "DDE Disconnect Success."     Else       Debug.Print "DDE Disconnect Failure."       TranslateError     End If          g_hDDEConv = 0      End If End Sub Private Sub DDE_StartAdvise()    Dim lRet As Long Dim lTransVal As Long   DDE_CreateStringHandles Text1.Text, Text2.Text, Combo1.Text      ' Open the conversation.   If (g_hDDEConv = 0) Then     g_hDDEConv = DDE_Connect   End If      If g_hDDEConv Then        ' Perform the transaction.     lRet = DdeClientTransaction(0, 0, g_hDDEConv, g_hItem, CF_TEXT, XTYP_ADVSTART, 2000, lTransVal)          If (lRet) Then            Debug.Print "DDE Advise Start Success."                    ' Enable the Advise Stop button and disable the Advise Start button.       Command7.Enabled = True       Command6.Enabled = False            Else       Debug.Print "DDE Advise Start Failure."     End If   End If      DDE_FreeStringHandles    End Sub Private Sub DDE_StopAdvise() Dim lRet As Long Dim lTransVal As Long      DDE_CreateStringHandles Text1.Text, Text2.Text, Combo1.Text        If g_hDDEConv Then        lRet = DdeClientTransaction(0, 0, g_hDDEConv, g_hItem, CF_TEXT, XTYP_ADVSTOP, 2000, lTransVal)          If (lRet) Then       Debug.Print "DDE Advise Stop Success."                    ' Disable the Advise Stop button.       Command7.Enabled = False       Command6.Enabled = True            Else       Debug.Print "DDE Advise Stop Failure."     End If   End If      DDE_FreeStringHandles End Sub Private Function CheckData(sCommand As String) As Boolean    Dim bRet As Boolean   Select Case sCommand     Case "Execute"       If (Text1.Text <> "") And (Text2.Text <> "") Then         bRet = True       End If            Case "Poke", "Request", "Advise"       If (Text1.Text <> "") And (Text2.Text <> "") And (Combo1.Text <> "<None>") Then         bRet = True       End If          End Select   CheckData = bRet    End Function Private Sub TranslateError()    Dim lRet As Long      lRet = DdeGetLastError(g_lInstID)   Select Case lRet     Case DMLERR_NO_ERROR       Debug.Print "DMLERR_NO_ERROR"            Case DMLERR_ADVACKTIMEOUT       Debug.Print "DMLERR_ADVACKTIMEOUT"            Case DMLERR_BUSY       Debug.Print "DMLERR_BUSY"          Case DMLERR_DATAACKTIMEOUT       Debug.Print "DMLERR_DATAACKTIMEOUT"          Case DMLERR_DLL_NOT_INITIALIZED       Debug.Print "DMLERR_NOT_INITIALIZED"          Case DMLERR_DLL_USAGE       Debug.Print "DMLERR_USAGE"          Case DMLERR_EXECACKTIMEOUT       Debug.Print "DMLERR_EXECACKTIMEOUT"          Case DMLERR_INVALIDPARAMETER       Debug.Print "DMLERR_INVALIDPARAMETER"          Case DMLERR_LOW_MEMORY       Debug.Print "DMLERR_LOW_MEMORY"          Case DMLERR_MEMORY_ERROR       Debug.Print "DMLERR_MEMORY_ERROR"          Case DMLERR_NOTPROCESSED       Debug.Print "DMLERR_NOTPROCESSED"          Case DMLERR_NO_CONV_ESTABLISHED       Debug.Print "DMLERR_NO_CONV_ESTABLISHED"          Case DMLERR_POKEACKTIMEOUT       Debug.Print "DMLERR_POKEACKTIMEOUT"          Case DMLERR_POSTMSG_FAILED       Debug.Print "DMLERR_POSTMSG_FAILED"          Case DMLERR_REENTRANCY       Debug.Print "DMLERR_REENTRANCY"          Case DMLERR_SERVER_DIED       Debug.Print "DMLERR_SERVER_DIED"          Case DMLERR_SYS_ERROR       Debug.Print "DMLERR_SYS_ERROR"          Case DMLERR_UNADVACKTIMEOUT       Debug.Print "DMLERR_UNADVACKTIMEOUT"          Case DMLERR_UNFOUND_QUEUE_ID       Debug.Print "DMLERR_UNFOUND_QUEUE_ID"   End Select    End Sub Private Sub Form_Load()   Text1.Text = "MyServer"   Text2.Text = "MyTopic"   Text3.Text = "Hello Server..."   Me.Caption = "DDE Client"      Combo1.AddItem "<None>"   Combo1.AddItem "MyAdvise"   Combo1.AddItem "MyPoke"   Combo1.AddItem "MyRequest"   Combo1.ListIndex = 0      Command1.Caption = "Initialize"   Command2.Caption = "Execute"   Command3.Caption = "Poke"   Command4.Caption = "Request"   Command5.Caption = "UnInitialize"   Command6.Caption = "StartAdvice"   Command7.Caption = "StopAdvice"   Command8.Caption = "Clear"      Command1.Enabled = True   Command2.Enabled = False   Command3.Enabled = False   Command4.Enabled = False   Command5.Enabled = False   Command6.Enabled = False   Command7.Enabled = False   Command8.Enabled = False End Sub - Add the following code in module1 Click here to copy the following block Option Explicit Global g_lInstID As Long Global g_hService As Long Global g_hService2 As Long Global g_hTopic As Long Global g_hTopic2 As Long Global g_hItem As Long Global g_hDDEConv As Long Global g_hDDEConvList As Long Global g_hDDEPrevConv As Long Global g_aryConvID() As Long ' See note in Command4_Click() concerning the magic number. Public Const MAGIC_NUMBER = 3 '************************************************************************* ' DDEML Return Values '************************************************************************* Public Const DMLERR_NO_ERROR = 0 Public Const DMLERR_ADVACKTIMEOUT = &H4000 Public Const DMLERR_BUSY = &H4001 Public Const DMLERR_DATAACKTIMEOUT = &H4002 Public Const DMLERR_DLL_NOT_INITIALIZED = &H4003 Public Const DMLERR_DLL_USAGE = &H4004 Public Const DMLERR_EXECACKTIMEOUT = &H4005 Public Const DMLERR_INVALIDPARAMETER = &H4006 Public Const DMLERR_LOW_MEMORY = &H4007 Public Const DMLERR_MEMORY_ERROR = &H4008 Public Const DMLERR_NOTPROCESSED = &H4009 Public Const DMLERR_NO_CONV_ESTABLISHED = &H400A Public Const DMLERR_POKEACKTIMEOUT = &H400B Public Const DMLERR_POSTMSG_FAILED = &H400C Public Const DMLERR_REENTRANCY = &H400D Public Const DMLERR_SERVER_DIED = &H400E Public Const DMLERR_SYS_ERROR = &H400F Public Const DMLERR_UNADVACKTIMEOUT = &H4010 Public Const DMLERR_UNFOUND_QUEUE_ID = &H4011 '************************************************************************* ' DDEML Flags '************************************************************************* Public Const XCLASS_BOOL = &H1000& Public Const XCLASS_DATA = &H2000& Public Const XCLASS_FLAGS = &H4000& Public Const XCLASS_NOTIFICATION = &H8000& Public Const XTYPF_NOBLOCK = &H2&  ' CBR_BLOCK doesn't seem to work Public Const XTYP_ADVDATA = (&H10& Or XCLASS_FLAGS) Public Const XTYP_ADVREQ = (&H20& Or XCLASS_DATA Or XTYPF_NOBLOCK) Public Const XTYP_ADVSTART = (XCLASS_BOOL Or &H30&) Public Const XTYP_ADVSTOP = (XCLASS_NOTIFICATION Or &H40&) Public Const XTYP_CONNECT = (XCLASS_BOOL Or &H60& Or XTYPF_NOBLOCK) Public Const XTYP_CONNECT_CONFIRM = (XCLASS_NOTIFICATION Or &H70& Or XTYPF_NOBLOCK) Public Const XTYP_DISCONNECT = (XCLASS_NOTIFICATION Or &HC0& Or XTYPF_NOBLOCK) Public Const XTYP_ERROR = (XCLASS_NOTIFICATION Or &H0& Or XTYPF_NOBLOCK) Public Const XTYP_EXECUTE = (XCLASS_FLAGS Or &H50&) Public Const XTYP_MASK = &HF0& Public Const XTYP_MONITOR = (XCLASS_NOTIFICATION Or &HF0& Or XTYPF_NOBLOCK) Public Const XTYP_POKE = (XCLASS_FLAGS Or &H90&) Public Const XTYP_REGISTER = (XCLASS_NOTIFICATION Or &HA0& Or XTYPF_NOBLOCK) Public Const XTYP_REQUEST = (XCLASS_DATA Or &HB0&) Public Const XTYP_SHIFT = 4 ' shift to turn XTYP_ into an index Public Const XTYP_UNREGISTER = (XCLASS_NOTIFICATION Or &HD0& Or XTYPF_NOBLOCK) Public Const XTYP_WILDCONNECT = (XCLASS_DATA Or &HE0& Or XTYPF_NOBLOCK) Public Const XTYP_XACT_COMPLETE = (XCLASS_NOTIFICATION Or &H80&) Public Const CP_WINANSI = 1004   ' Default codepage for DDE conversations. Public Const CP_WINUNICODE = 1200 Public Const CF_TEXT = 1 Public Const CBF_SKIP_ALLNOTIFICATIONS = &H3C0000 Public Const APPCLASS_MONITOR = &H1 Public Const APPCMD_CLIENTONLY = &H10& Public Const MF_CALLBACKS = &H8000000 Public Const MF_CONV = &H40000000 Public Const MF_ERRORS = &H10000000 Public Const MF_HSZ_INFO = &H1000000 Public Const MF_LINKS = &H20000000 Public Const MF_POSTMSGS = &H4000000 Public Const MF_SENDMSGS = &H2000000 Public Const TIMEOUT_ASYNC = &HFFFF Public Const QID_SYNC = &HFFFF Public Const DDE_FACK = &H8000 Public Const DDE_FBUSY = &H4000 Public Const DDE_FNOTPROCESSED = &H0 Public Const EC_ENABLEALL = 0 '************************************************************************* ' DDEML Type Declarations '************************************************************************* Public Type SECURITY_QUALITY_OF_SERVICE   Length As Long   Impersonationlevel As Integer   ContextTrackingMode As Integer   EffectiveOnly As Long End Type Public Type CONVCONTEXT   cb As Long   wFlags As Long   wCountryID As Long   iCodePage As Long   dwLangID As Long   dwSecurity As Long   qos As SECURITY_QUALITY_OF_SERVICE End Type Public Type CONVINFO   cb As Long   hUser As Long   hConvPartner As Long   hszSvcPartner As Long   hszServiceReq As Long   hszTopic As Long   hszItem As Long   wFmt As Long   wType As Long   wStatus As Long   wConvst As Long   wLastError As Long   hConvList As Long   ConvCtxt As CONVCONTEXT   hwnd As Long   hwndPartner As Long End Type '************************************************************************* ' DDEML Function Declarations '************************************************************************* Public Declare Function DdeInitialize Lib "user32" Alias "DdeInitializeA" _   (pidInst As Long, _   ByVal pfnCallback As Long, _   ByVal afCmd As Long, _   ByVal ulRes As Long) As Integer    ' Removed the alias. Public Declare Function DdeUninitialize Lib "user32" _   (ByVal idInst As Long) As Long    ' Removed the alias. Public Declare Function DdeConnect Lib "user32" _   (ByVal idInst As Long, _   ByVal hszService As Long, _   ByVal hszTopic As Long, _   pCC As Any) As Long    ' Removed the alias. Public Declare Function DdeDisconnect Lib "user32" _   (ByVal hConv As Long) As Long    Public Declare Function DdeCreateStringHandle Lib "user32" Alias "DdeCreateStringHandleA" _   (ByVal idInst As Long, _   ByVal psz As String, _   ByVal iCodePage As Long) As Long    ' Removed the alias. Public Declare Function DdeFreeStringHandle Lib "user32" _   (ByVal idInst As Long, _   ByVal hsz As Long) As Long        ' Removed the alias and changed the first parameter from "ByRef pData as Byte" ' to "ByVal pData as String". Public Declare Function DdeClientTransaction Lib "user32" _   (ByVal pData As String, _   ByVal cbData As Long, _   ByVal hConv As Long, _   ByVal hszItem As Long, _   ByVal wFmt As Long, _   ByVal wType As Long, _   ByVal dwTimeout As Long, _   pdwResult As Long) As Long    ' The API loader provides an alias of "DdeGetDataA" for this function. ' You need to remove it because the DLL entry point can't be found for ' the alias. Public Declare Function DdeGetData Lib "user32" _   (ByVal hData As Long, _   ByVal pDst As String, _   ByVal cbMax As Long, _   ByVal cbOff As Long) As Long Public Declare Function DdeQueryConvInfo Lib "user32" _   (ByVal hConv As Long, _   ByVal idTransaction As Long, _   pConvInfo As CONVINFO) As Long Public Declare Function DdeQueryNextServer Lib "user32" _   (ByVal hConvList As Long, _   ByVal hConvPrev As Long) As Long Public Declare Function DdeConnectList Lib "user32" _   (ByVal idInst As Long, _   ByVal hszService As Long, _   ByVal hszTopic As Long, _   ByVal hConvList As Long, _   pCC As CONVCONTEXT) As Long Public Declare Function DdeDisconnectList Lib "user32" _   (ByVal hConvList As Long) As Long Public Declare Function DdeQueryString Lib "user32" _   Alias "DdeQueryStringA" _   (ByVal idInst As Long, _   ByVal hsz As Long, _   ByVal psz As String, _   ByVal cchMax As Long, _   ByVal iCodePage As Long) As Long ' Removed the alias. Public Declare Function DdeFreeDataHandle Lib "user32" _   (ByVal hData As Long) As Long ' Removed the alias. Public Declare Function DdeGetLastError Lib "user32" _   (ByVal idInst As Long) As Long Public Declare Function DdeEnableCallback Lib "user32" _   (ByVal idInst As Long, _   ByVal hConv As Long, _   ByVal wCmd As Long) As Long Public Function DDECallback(ByVal uType As Long, ByVal uFmt As Long, ByVal hConv As Long, ByVal hszString1 As Long, ByVal hszString2 As Long, ByVal hData As Long, ByVal dwData1 As Long, ByVal dwData2 As Long) As Long    Dim lSize As Long Dim sBuffer As String Dim Ret As Long      Debug.Print "In client callback. uType: " & uType      Select Case uType          ' This is th eevent you'll receive when a server sends you a advisment.     Case XTYP_ADVDATA       Debug.Print "XTYP_ADVDATA"              lSize = DdeGetData(hData, vbNullString, 0, 0)              ' If size is 0 then there's no data to grab.       If (lSize > 0) Then                  ' Allocate a buffer for the return data.         sBuffer = String$(lSize - MAGIC_NUMBER, 0)                        ' Grab the data.         lSize = DdeGetData(hData, sBuffer, Len(sBuffer), 0)            ' Print the contents of the buffer.         Form1.Text3.Text = sBuffer       End If            Case XTYP_ADVSTART       Debug.Print "XTYP_ADVSTART"            Case XTYP_ADVSTOP       Debug.Print "XTYP_ADVSTOP"          Case XTYP_CONNECT       Debug.Print "XTYP_CONNECT"            Case XTYP_CONNECT_CONFIRM       Debug.Print "XTYP_CONNECT_CONFIRM"            Case XTYP_DISCONNECT       Debug.Print "XTYP_DISCONNECT"            Case XTYP_ERROR       Debug.Print "XTYP_ERROR"            Case XTYP_EXECUTE       Debug.Print "XTYP_EXECUTE"            Case XTYP_MASK       Debug.Print "XTYP_MASK"            Case XTYP_MONITOR       Debug.Print "XTYP_MONITOR"            Case XTYP_POKE       Debug.Print "XTYP_POKE"            Case XTYP_REGISTER       Debug.Print "XTYP_REGISTER"       g_hService2 = hszString2              lSize = DdeQueryString(g_lInstID, hszString2, vbNullString, 0, CP_WINANSI)       sBuffer = Space(lSize)       DdeQueryString g_lInstID, hszString2, sBuffer, lSize + 1, CP_WINANSI       sBuffer = UCase(sBuffer)            Case XTYP_REQUEST       Debug.Print "XTYP_REQUEST"            Case XTYP_SHIFT       Debug.Print "XTYP_SHIFT"            Case XTYP_UNREGISTER       Debug.Print "XTYP_UNREGISTER"            Case XTYP_WILDCONNECT       Debug.Print "XTYP_WILDCONNECT"            Case XTYP_XACT_COMPLETE       Debug.Print "XTYP_XACT_COMPLETE"            End Select      DDECallback = 0 End Function - Now compile the project and run the DDEServer.exe and then run DDEClient.exe In this version of DDE Client I have added few commands for demo which our DDE Server understands. Here is the description of each option (Select this command from combo box) : This command will enable execute command button. For demo purpose I have added "MIN", "MAX" and "NORMAL" commands which DDL Server can understand. Just type any of these commands in the Data textbox and then press execute and see what server does to respond your command. MyRequest : Clicking on Request button will request data from server and displays in the textbox on client side MyPoke : This is just demo of sending data to the server. Try to enter some text in Text3 and then press Poke. Now check the server window, your text should appear in server data textbox. MyAdvise : This command will start Advisory request from DDE server means server will send data to client when its available/changed. Goto Previous Article : Interprocess communication using DDE (Dynamic Data Exchange) - Part1

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Interprocess communication using DDE (Dynamic Data Exchange) - Part1

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