Detection of changes made in Autocad/Civil 3D with .NET
You may want to provide more description on the situation when/why you need to know a point group (or any object, for that matter) is added, modified or deleted. What role the form (your custom UI, obviously) plays in this situation (how the UI is displayed make HUGE difference here: being modeless or modal!), because it seems only the UI need to show the point group information and the potential changes.
If you show the UI as modal (i.e. a Dialog box), then point groups in the drawing CANNOT BE CHANGED/ADDED/DELETED, UNELSS the action is triggered by the UI itself (say, user clicks a button to add/change/delete), therefore, your code knows when the changes occur.
If the UI is modeless, then things are quite complicated. You need to handle various events (Entity.ObjectModified, or Database.ObjectAppended/Modified/Erased), or you may try to use ObjectOverrule to monitor the possible changes and decide a proper way to do (or not to do) something once changes are detected. This monitoring/handling work should have nothing to do with your modeless UI, but you probably need to decide whether the UI needs a refresh or not. As I said, it is rather complicated/advanced AutoCAD programming task. Not sure what your skill level is, I just stop here.
Based on what you described, I assume you want to have a modeless form/PaletteSet to show/monitor current status of PointGroups in drawing. That is, when a PointGroup is added, existing one is modified (name change, for example) or erased; or even the CogoPoints in a group is changed, you want to form view updated automatically. The UI would behave just like Properties window, but only show CogoPoint/PointGroup information. It, of course, can be done with Acad/C3d .NET API, but it is a quite involving task.
To do this type task, it would be very important to structure your solution properly to separate the functionality of the operation. Here is roughly I'd do:
1. Create a functional component (one or more classes) that handle the change tracking work
- add handlers to Database.ObjectAppended/ObjectModified/ObjectErased events
- Inside the event handlers, examine the e.DBObject is PointGroup/CogoPoint or not. If yes, save the ObjectId of them into a corresponding collections
- When the first affected ObjectId is collected, add handler to Application.Idle event (you probably want to set a flag indicating this idle event handler is set because of affected ObjectId has been collected and waiting for current operation, likely a executing command, to be finished)
- Once idle event handler runs, you examine the collected ObjectIds to see which CogoPoint/PointGroup added/modified/erase and organize the updated information into a data model. Then you move the idle event handler
- Once the updated information data model is ready, raise a custom event with the data model as event argument
2. Build the modeless UI. It would much better to use WPF in MVVM pattern, so, that you can have the ViewModel to subscribe the aforementioned custom event. that is, whenever the tracking component raises its "change" event, the ViewModel would use the data model passed through the event argument to update itself, thus the UI.
As you can see, you at least structure the code into 2 separate parts/components (change tracking and change presenting) and the 2 would only loosely couple together with event subscription and the common knowledge for both side is the updated information data model. Thus code modification on either side would have no, or minimum impact to the other.
If you wan to tracking other C3D objects, such as Parcel/Network... things could get event more complicated. For example, ParcelSegment change (adding/modifying/erasing) would not limited to itself, it would also affect one or more Parcels (being added/modified/deleted).
Not sure my description make how much sense to you or not. If not much, you may still have a lot to study up to the task, I am afraid.
