DDE connections and links

Before you can exchange any data between two DDE applications, you must establish a communication connection. To establish a communication connection, you must specify a Server name and Topic. You can specify the Server name and Topic for VA Smalltalk DDE parts in their settings. It is the responsibility of the DDE client part to create a communication connection, and the DDE server must already be running for this to occur successfully.

A connection is created for a single Server name and a single Topic. Applications that need to communicate on more than one topic must create a connection for each topic. VA Smalltalk DDE Server parts can support multiple topics and multiple connections. VA Smalltalk DDE Client parts can support only a single topic and a single connection.

For each Item-Format combination that is exchanged, DDE creates a link. VA Smalltalk automatically creates all necessary DDE links for you.

Starting a DDE server application

For communication to be successful, the server application must be running at the time a DDE client makes a connection. Either the end user or the DDE client application must start the server application.

The VA Smalltalk DDE Client part has features to help you start any DDE server application. The features are as follows:

Server program name

The program to start, such as EXCEL.EXE

Server program timeout (ms)

The time, in milliseconds, that will elapse before the VA Smalltalk DDE client considers the DDE server application not startable.

Number of server startup retries

The number of times, within the Server program timeout (ms) interval that VA Smalltalk will check to see whether the DDE server is running.

Server program input

A command line parameter to be passed to the application. For example, mysheet.xls can be passed to Excel. This is equivalent to typing excel mysheet.xls at a command prompt.

Connected server initial command

A command to be sent to the server, using DDE, before the DDE client attempts to connect to the DDE server. For example, run macro ddx] can be sent to Excel before attempting to create the DDE connection.

You can specify these values in the DDE Client part's settings notebook. Because your DDE Client part and DDE Server part are within the same application, you do not need to specify these settings here.