'InstanceFactoryChoice' object has no attribute 'object'

[hopeful0]

I noticed that the InstanceFactoryChoice class doesn't work properly when using the selection feature of InstanceEditor. The error message is as follows:

File ".../python3.9/site-packages/traitsui/qt4/instance_editor.py", line 185, in _get_items
    value.object.observe(
AttributeError: 'InstanceFactoryChoice' object has no attribute 'object'

The test examples (instance_editor_test2.py/instance_editor_test4.py/instance_editor_test5.py) in integrationtests/ui which use InstanceFactoryChoice also trigger this error.

I checked the source code and found that the problem was caused by pull request #1725 which fixed issue #1641. In that pull request, a listener was added for the object trait of InstanceChoiceItem instance value . However, this trait is only defined in InstanceChoice and not in other subclasses like InstanceFactoryChoice, which dynamically retrieves the object through the get_object() method.

Therefore, a type check should be added to avoid this problem:

if isinstance(value, InstanceChoice):
    value.object.observe(
        ...