HP NonStop G-Series - Manual (Page 101)

Microsoft Visual Basic UMS Client Applications
Using DDE Hot and Warm Data Links
110838 Tandem Computers Incorporated 7–5
DDE-NUM-TIMES-DELIVERED is the number of DDE conversations over which the
message data was delivered to client applications. The value is zero if no client has a
DDE hot or warm link to the message.
Developing Client
Applications to
Receive UMS
Messages
To receive UMS messages in your client application, create a DDE hot or warm data
link using a DDE item name that matches the DDE-ITEM-NAME field of the message
created on the Tandem system.
Each client tool is different in the way it makes DDE hot and warm links. See
Section 1, “Introduction to the Tandem DDE Gateway,” for examples. For more help,
consult the index of your client tool’s manual under “dynamic-data exchange,” “DDE
hot links,” “DDE warm links,” and “advise links.” Topics such as “communicating
with other applications” can also be helpful.
Use the following parameters when you start a DDE hot or warm data link:
1. DDE application name = TDMGW
2. DDE topic name = UMS
3. DDE item name = DDE-ITEM-NAME from the UMS message
Immediately after making a DDE hot or warm data link, client tools often request the
current value of the data item. Because data will not have arrived from the Tandem
system yet, the Tandem DDE Gateway returns a zero length data item. Check for this
in the client tool so that you do not process this zero length data as if it were
application data.
Microsoft Visual Basic
UMS Client
Applications
Microsoft Visual Basic 2.0 establishes a DDE link using the LinkMode property of a
control. If you use the value 1 for the LinkMode property, a DDE hot link is
established and when a UMS message arrives, the data from the message is placed in
the linked control and a “change” event occurs. If you use the value 3 for the
LinkMode property, a DDE warm link is established and when a UMS message
arrives, a “LinkNotify” event occurs. You can obtain the data from the message using
the LinkRequest method. DDE warm links are called DDE Notify links by Visual
Basic.
Timeouts can occur if you use DDE hot links and then attempt other DDE operations
such as using the Tandem DDE Gateway to communicate with a Tandem server
within the “change” event procedure. This is a feature of Visual Basic; it behaves in
the same manner when using Microsoft Excel as a DDE server.
If you wish to perform DDE operations within the “change” event procedure of a
control with a DDE hot link, use the DDE warm (“Notify”) link option and
“LinkNotify” event procedure instead.
Note The preceding consideration is based on Microsoft Visual Basic release 3.0. Other releases of Microsoft
Visual Basic may not operate in the same manner.