August 3, 2016 | Stepan Drzka
In Reliance projects, a link to an object (a tag, picture, etc.) is generally the definition of how a single object is linked to another (target) object. One example of such a link is a visualization window with a Display component linked to a tag. Up to Reliance 4.7.1, all links to objects had been static. This means that a link was defined as fixed at design-time and could not be changed at runtime. In later versions of Reliance, it is possible to define some links as dynamic (they are sometimes called as indirect links). In dynamic links to objects, the target object is specified by the name (by the value of the control tag). The control tag is of type String. In practice, this means that when specifying the link, for example, to a picture, the systems integrator chooses a tag the value of which will correspond to the name of the picture. The real link to an object will be evaluated at runtime each time the control tag value changes.
The Container component allows you to dynamically control a structured tag linked to a window template. Thus, when you change the value of the control tag, you can “switch” between individual structured tags and display their data using a single Container component. The control tag's value can be easily set, for example, by using the Combo Box component. Support for dynamic links to structured tags was added to the Container component in version 4.7.2.
Among other things, the Container component allows you to insert the list of current alarms/events into the window. You can filter what you want to display (devices, alarm/event types, alarm/event groups). The filter can be changed dynamically through alarm/event groups. The control tag's value corresponds to the list of the names of alarm/event groups separated by commas. So, once you change the value of the control tag, the inserted list of current alarms/events is updated. The control tag's value can be easily set, for example, by using a new action named Select alarm/event groups. This action displays the standard object selection dialog and stores the result of the selection in the chosen (control) tag. Support for dynamic links to alarm/event groups was added to the Container component in version 4.7.3.
The Picture component allows you to control the link to the displayed picture. The value of the control tag can be either the name of the project-defined picture, the name of the picture file, or the Web address of the picture (URL). Support for dynamic links to pictures was added to the Picture component in version 4.7.1.
Dynamic links can be a powerful tool when creating visualization projects. The only drawback of using dynamic links is the fact that, in principle, project diagnostics cannot check the correctness of dynamic linking. Likewise, project diagnostics cannot check in advance whether an object is used within the project. This means that some objects can be marked as unused, but they are used through a dynamic link.