Sharepoint LookUp field on Choice field?

You can use calculated column is source list, that will display value of Choice column. Then you can add lookup column for this calculated field. It will work only for Choice column with single selection. For multiple selection you can use 3rd party components like that: http://www.sparqube.com/SharePoint-Lookup-Column

the programmatical Solution is at risk to run into an endless recursion:

The ItemAdded Event and UpdatedEvents are asynchrone. This means, that the command: this.EventFireingEnabled = false is not threadsafe. After systemUpdate you set EventFireingEnabled to true.

But because the ItemUpdated is asynchronus, you cannot guarantee, that the ItemUpdated for your system.update has already been called at this time!.

It is not possible to create a lookup field for a choice (dropdown) field. There are two ways to resolve your problem: The programmatic approach and the workaround.

The programmatic approach involves an creating event receiver to do the magic - pretty work intensive. But there is an explanation here:

• Sharepoint 2010 - How to use List Events to Set a Column's Value using Visual Studio 2010 (C#)

You can also just create another list, containing your choice field values and use a calculated field as a source for your lookup column. Check out the following explanation:

• Using a lookup field on a choice field workaround