Design Pattern: Unbound Item (aka Virtual Item)

virtualitems
designpattern
Tags: #<Tag:0x00007f0146be4e68> #<Tag:0x00007f0146be4b98>

(Rich Koshak) #1

Problem Statement

Sometimes one needs to create a flag, control, switch, or some other control that is not bound to a device or channel. For example, a Switch to override presence detection.

Concept

Create an Item that does not have a binding configuration.

Simple Example

Switch VirtualItem "label" <icon> (groups) // No binding config

See the Sensor Aggregation Design Pattern for a more complicated example. The Virtual Item is Override_Presence in that example.

Advantages and Limitations

Virtual Items are a good way to store state needed by rules and to provide a way to allow the user to modify the behavior of their rules by adjusting parameters stored in Virtual Items. Data stored in Virtual Items can also be persisted and restored on startup unlike global vars and vals.

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(YvesHanoulle) #2

Data stored in Virtual Items can also be persisted and restored on startup unlike global vars and vals.

You might want to add how to do that.

I have figured out, by adding it to a group that was persisted and that group had restoreOnStartup in the .persiste file.

Yet it took me a long time to find that.