Manage a Datafeed with Messages

A Datafeed object responds to several messages, including Connect and Set Script. These are detailed above as arguments for Open Datafeed. They can also be sent as messages to a Datafeed object that already exists:

feed << Connect( port( "com1:" ), baud( 4800 ), databits( 7 ), parity( odd ), stopbits( 2 ) );

feed << Set Script( myScript );

The following messages could also be used as arguments to On Data Feed. However, it would be more common to send them as messages to a Datafeed object that is already present.

You can send lines to a Datafeed from a script. This is a quick way to test a Datafeed. Include a text argument or a global that stores text:

feed << Queue Line( "14" );

feed << Queue Line( myValue );

Here is a test script to queue five lines of data:

feed << Queue Line( "11" );

feed << Queue Line( "22" );

feed << Queue Line( "33" );

feed << Queue Line( "44" );

feed << Queue Line( "55" );

Datafeed: 5 Lines Queued

To get the first line currently waiting in the queue, use a Get Line (singular) message. When you get a line, it is removed from the queue. Five lines were queued with the test script above, and Get Line returns the first line and removes it from the queue:

feed << Get Line

"11"

Datafeed: 4 Lines Queued

To empty all lines from the queue into a list, use Get Lines (plural). This returns the next four lines from the test script in list { } format.

myList = feed << GetLines;

{ "22", "33", "44", "55" }

Datafeed: 0 Lines Queued

To stop and later restart the processing of queued lines, either click the Stop and Restart buttons in the Datafeed window, or send the equivalent messages:

feed << Stop;

feed << Restart;

To close the Datafeed and its window:

feed << Close;

To disconnect from the live data source:

feed << Disconnect