I have a display showing PV and SP for 10 out of 1000 PID blocks. It displays correctly, but I want to change the SP of the tag. Since the format of my tags is “PDxxxx”, I use an expression binding using the index for the associated display element as shown. The problem is that unlike tag binding, expression binding does not provide a bidirectional ability in the Text Field component.
Is there a way to provide bidirectional SP change in this application?
Don’t use the tag() expression function. (Like, never.) It exists for backwards compatibility. Use indirect tag binding instead, where all or part of the tag path is kept in a separate custom string property. Indirect tag bindings can be bidirectional.
I don’t know if I chose the best way to do it, but here is what I did:
- Created 10 integer tags (PDIndex) to hold the index of the PID loop
- Created 10 expression tags (PDTag) to convert the 10 PDIndex tags to a string with the tag path to the PID SP tag
- Created 10 custom properties (PDTag) of type string on the root of the window with a binding to the PDTags
- Bound the Text Field components to the custom property PDTags
Most wouldn’t bother with the integer tags and expression tags – they just make the window only usable by one client at a time. The common approach would be to leave the strings unbound, supplying them as parameters to the window. In any case, you can convert integers to strings with a binding expression instead of an expression tag.
Bumping for the Perspective crowd, this works beautifully in perspective.