Why does this customized selector attribute not allow selection?

@darylbowman  Here is the solution for the above issue.

1. Few modifications in the Custom Selector (For testing purposes, I have removed the Where condition and verified)
2. In the .aspx page, Change the SegementMask to Selector control.

Here is the updated code.

public class DSRestrictActivityProjects_CRActivityMaint_Ext : PXGraphExtension<CRActivityMaint>
    {
        [PXMergeAttributes(Method = MergeMethod.Append)]
        [PXRemoveBaseAttribute(typeof(EPProjectAttribute))]
        [CustomerProjects(typeof(PMProject.contractID))]
        protected virtual void _(Events.CacheAttached<PMTimeActivity.projectID> e)
        { }

        public class CustomerProjects : PXCustomSelectorAttribute
        {
            private PXView _view;
            public CustomerProjects(Type type) : base(type, typeof(PMProject.contractCD),
                                                 typeof(PMProject.description),
                                                 typeof(PMProject.status))
            {
                  SubstituteKey = typeof(PMProject.contractCD);
                //DescriptionField = typeof(PMProject.description);
            }


            public virtual IEnumerable GetRecords()
            {
                //CRActivity activity = (CRActivity)_Graph.Views["CurrentActivity"].Cache.Current;
                //if (activity is null || activity?.RefNoteID is null)
                //    return null;

                return SelectFrom<PMProject>.
                    LeftJoin<CRCase>.
                        On<CRCase.customerID.IsEqual<PMProject.customerID>>.
                    Where<PMProject.baseType.IsEqual<CTPRType.project>
                        //And<CRCase.noteID.IsEqual<@P.AsGuid>>
                        >.
                    // View.Select(_Graph, activity.RefNoteID).FirstTableItems;
                    View.Select(_Graph).FirstTableItems.ToList();
            }
        }
    }

I have two issues with your solution:

1. I’m a little bit hesitant to change the field type. It seems like there would be a reason they used the field type they did, or issues if it were changed?
2. I tried removing the ‘where’, and while it does show projects, it does not show only projects for the current Customer if the current Activity is tied to a Case, which was the original goal

So using your observations, I instead tried implementing a customized PXDimensionSelector like this:

public class CustomerProjects2 : PXCustomDimensionSelectorAttribute
{
    public CustomerProjects2()
        : base("PROJECT", typeof(PMProject.contractID),
                typeof(PMProject.contractCD),
                typeof(PMProject.contractCD),
                typeof(PMProject.description),
                typeof(PMProject.status))
    { }

    public override IEnumerable GetRecords()
    {
        CRActivity activity = (CRActivity)*noGraph*.Views["CurrentActivity"].Cache.Current;
        if (activity is null || activity?.RefNoteID is null)
            return null;

        return SelectFrom<PMProject>.
            LeftJoin<CRCase>.
                On<CRCase.customerID.IsEqual<PMProject.customerID>>.
            Where<PMProject.baseType.IsEqual<CTPRType.project>.And<CRCase.noteID.IsEqual<@P.AsGuid>>>.
            View.Select(new PXGraph(), activity.RefNoteID).FirstTableItems;
    }
}

The problem is, there is no ‘_Graph’ attribute that I can find to allow getting the current Activity, which means the results are not filtered.

I also can’t find any documentation for this situation.