Item Lists of Combo Box/Ring Constants Do Not Update from Type Definitions

Issue Details

I have a Type Definition that includes a Combo Box or Ring Control, and I have created a constant from that type definition on the block diagram of a VI. If I edit the item names of the Combo Box or Ring Control in the type definition, LabVIEW does not automatically update the linked constant. Why is this happening?

Solution

This behavior is expected. The basic Type Definition functionality of Combo Boxes and Rings is described by the Type Definition documentation in the LabVIEW Help:

To illustrate this concept:

1. Open the context help window in LabVIEW by selecting Help>>Show Context Help.
2. Hover over a wire coming out of a Combo Box or Ring Control on the Block Diagram.

The data type of a Combo Box is a standard string, and a Ring Control is a standard numeric (such as a 16-bit unsigned integer). Because standard strings and integers do not contain item name configurations in their underlying data types, changes to the item names do not propagate as data type changes. Changing the representation of a Ring Control (e.g., from U16 to I32) will automatically update the constant because representation is a fundamental property of the numeric data type.

Use Enums instead of Combo Boxes or Rings

Unlike Combo Boxes and Rings, enums have their own distinct enum data type that includes both the numeric value and the associated string labels. Because of this, changes to enum item names in a Type Definition will automatically propagate to all instances, including block diagram constants. To access the selected item's string label from an enum on the block diagram, wire the Enum terminal to the input of the Format Into String function.

Additional Information

Block Diagram constants cannot be strict type definitions. When a constant is tied to a strict type definition, LabVIEW down-casts the constant to a regular type definition. If you need to share the same list of strings across multiple front panels, define the source list in a single configuration file or control, and use the strings property node to copy the list to other controls at startup.