ADT: How to Direct DDE to a Specific Instance of a Server (105659)

MORE INFORMATION

Each instance of each application started in Windows is assigned a unique number called a Task ID. This number can be used to distinguish among multiple instances of an application.

To initiate a DDE conversation using the System topic with an instance of Microsoft Excel that has a Task ID of 34567, you could use the following sample command:

   Chan = DDEInitiate("excel34567", "System")
				

If you do not specify a Task ID number, you will initiate a conversation with the first instance of the application that Windows finds. Note that the order in which Windows finds instances of an application does not always correspond to the order in which the applications were started.

How to Get the Task ID of an Application

You can get the Task ID of an application by doing one of the following:

• Use the Access Basic shell command to launch the application. The shell command will return the application's Task ID if the application is launched successfully. -or-
  
  
• Use an Access Basic function to find the Task ID. The following sample function can be used to find an application's Task ID:

Notes

• In the following sample code, an underscore (_) is used as a line- continuation character. Remove the underscore from the end of the line when re-creating this code in Access Basic.
• You may have some Microsoft Windows API functions defined in an existing Microsoft Access library; therefore, your declarations may be duplicates. If you receive a duplicate procedure name error message, remove or comment out the declarations statement in your code.

        Option Explicit
  
        Declare Function GetActiveWindow Lib "User" () As Integer
        Declare Function GetWindowWORD Lib "User" (ByVal hWnd As Integer, _
           ByVal nIndex As Integer) As Integer
        Const GWW_HINSTANCE = (-6)
  
        Function GetActiveTaskID ()
           GetActiveTaskID = GetWindowWORD(GetActiveWindow(), _
              GWW_HINSTANCE)
        End Function
  					

The following Access Basic code demonstrates the use of both of these techniques in getting the Task ID:

   Function TestTaskID()
      Dim TaskID
      TaskID = Shell("excel", 1)
      MsgBox TaskID & " and " & GetActiveTaskID()
   End Function
				

How to Use an Application's Task ID in a DDE Conversation

The following example demonstrates how to use Task IDs to indicate which instance of an application should be used in a DDE conversation. This sample code will launch two instances of Microsoft Excel, start a DDE conversation with each instance, and poke data to Sheet1 of each instance:

   Function DDEWithTwoInstances ()
      Dim TaskID1, TaskID2
      Dim Chan1, Chan2

      ' Start 2 instances of Microsoft Excel and record Task ID numbers.
      TaskID1 = Shell("excel.exe", 1)
      TaskID2 = Shell("excel.exe", 1)

      ' Initiate DDE conversations with both instances using
      ' the Task ID numbers. Trap an error that may happen
      ' if we try to initiate a conversation and the copy of
      ' Microsoft Excel is still trying to start from the shell command.

      On Error GoTo ExcelNotYetReady
      Chan1 = DDEInitiate("excel" & TaskID1, "Sheet1")
      On Error GoTo 0

      On Error GoTo ExcelNotYetReady
      Chan2 = DDEInitiate("excel" & TaskID2, "Sheet1")
      On Error GoTo 0

      ' Poke information into each instance of Microsoft Excel.

      DDEPoke Chan1, "R1C1", "This is Task1!"
      DDEPoke Chan2, "R1C1", "This is Task2!"

      DDETerminateAll

      Exit Function

   ExcelNotYetReady:
      DoEvents
      Resume

   End Function