Tango ATK Tutorial

There are two kinds of errors in ATK. The first type of errors, called “Error”, is produced
when the Tango DevFailed Exception occurs during the reading of an attribute or during the
execution of a command. The second type of errors, called “SetError”, is produced when the
Tango DevFailed Exception occurs during the setting value of an attribute. This is done to be
able to make a clear separation between the errors which happen during the setting of an
attribute and those which happen during the reading of the same attribute.
In addition to the ATK error events generated, ATK provides two classes of error viewers :
ErrorHistory and ErrorPopup. They are the graphical viewer classes which listen to ATK
error events and display the error to the application end user.
How to handle and display errors
The provided error viewer classes can be used to collect and to display ATK errors generated
during the application session. Here are the steps to perform to handle errors :
• Create one or more ErrorViewer(s)
ErrorHistory errh = new ErrorHistory();
ErrorPopup errorpopup = ErrorPopup.getInstance();
• Add one or more error viewer(s) as error listeners to the empty attribute list just after
it’s instantiation
AttributeList attl = new AttributeList();
attl.addErrorListener(errh);
attl.addSetErrorListener(errorpopup);
attl.addSetErrorListener(errh);
• Add one or more error viewer(s) as error listeners to the empty command list just after
it’s instantiation
CommandList cmdl = new CommandList();
cmdl.addErrorListener(errh);
cmdl. addErrorListener (errorpopup);
• Connect to the attributes by adding them to the attribute list
attl.add(att_one);
attl.add(att_two);
…..
• Connect to the commands by adding them to the command list
cmdl.add(cmd_one);
cmdll.add(cmt_two);
…..
• Start the attribute list refresher
attl.startRefresher();
…..
The error viewers are registered as error listeners of the attribute list and the command list.
This way they will be registered as the error listeners of all the members added to these lists.
It is very important to register them as error listeners of the list before the first adding of the
elements.