When an external class is configured with the Unity Script option, a Unity script using the IWorkViewGetExternalClassData event must be created for the class.
You can launch Unity Script creation for an external class in the class creation wizard by selecting the Configure Unity Script option or by clicking the Modify button in the class's Connection tab.
After launching the script editor for this context, create the script and save and publish it.
You can edit the script by clicking the Modify button in the class's Connection tab.
Note:
The IWorkViewGetExternalClassData event cannot be removed from a class.