Through the Interface

18 responses to “Linking Circles, Part 1: Using .NET events to relate AutoCAD geometry”

1. 

   s.kaiser

   November 28, 2006 at 7:45 pm

   We use a similar mechanism extensively (with ObjectARX) for updating various relationships between objects.

   It would be interesting to get better (or 'clearer') information from AutoCAD in the case of copy operations (like 'onEndDeepClone()'). It can get more difficult if multiple databases are involved (e.g. copy'n'paste).

   Good topic! Looking forward to your next articles!

   Reply
2. 

   Kean Walmsley

   November 28, 2006 at 8:28 pm

   Thanks, Stephan!

   What is it you'd like to receive in that event, beyond the final, translated idMapping? (which doesn't appear to be passed to the .NET version of the callback - a separate issue I'm looking into).

   Regards,

   Kean

   Reply
   1. 

      Harsh

      September 2, 2020 at 4:46 am

      Hello Kean,
      Is this dynamic linking possible with 2 points? I have tried it but my condition to reduce the apart distance is not working.

      Reply
      1. 

         Kean Walmsley

         September 2, 2020 at 5:23 am

         Hi Harsh,

         I'm afraid I'm not working with AutoCAD, these days. Please post your support requests to the AutoCAD .NET forum.

         Thank you,

         Kean

         Reply
3. 

   s.kaiser

   November 30, 2006 at 11:41 pm

   It gets difficult to trace changes as the different cloning and copying mechanisms (copy'n'paste, insert, etc) use (slightly) different 'paths' through the code and, more importantly, also through the available callbacks.

   We solved it for now by storing ids of modified objects and handling various interactions in a 'commandEnded' callback.

   While this works fine for most cases, it breaks down for certain special copying operations. Supporting all of them is a pain. Furthermore, some operations would profit from access to a geometric acceleration structure.

   Anyway, a more pressing issue is that while curve-curve intersections can be done quite nicely through the AcGe API (though with a few workarounds for bugs in it) the support for curve-surface and especially surface-surface intersections seems not to be very good. This is very unfortunate. I'm currently evaluating different options (including AcBr) but it's difficult to get a feel for it as the docs leave a few interesting points out. 😉 Well, this is pretty off-topic. But maybe it's worth a blog entry in the future. 🙂

   Cheers

   Reply
4. 

   Brian

   February 19, 2007 at 5:44 am

   I was hoping to work out how to get the Entity from the handle and then erase it, from your posts, I've learned a lot but not found the answer to this one yet, I still have a mountain to climb. (I'm using VB.NET, I've done it in VB6 +COM, even in Lisp but .NET ....)

   Reply
5. 

   Kean Walmsley

   February 19, 2007 at 1:32 pm

   Hi Brian,

   Please see this post from today - I hope it answers your question:

   keanw.com/...

   Regards,

   Kean

   Reply
6. 

   sridharkumar

   March 28, 2007 at 7:52 am

   Sir
   My query is if i open a Auto CAD drawing and i want to transfer the dimesions from the drawing into an excel sheet using a .NET program.
   I was bit confused from where to start. can u please suggest me any thing regarding this
   Thanks
   Sridhr

   Reply
7. 

   Kean Walmsley

   March 30, 2007 at 6:42 am

   Hi Sridhar,

   You need to:

   1) Open the block table of the database.
   2) Open tha appropriate block table record or "space", whether modelspace or a layout.
   3) Iterate through the block table record (e.g. with a foreach statement), checking each object to see whether it's a dimension.
   4) Extract the infornation you want from each dimension, adding it to the Excel spreadsheet.

   The Ents sample (under samples/dotNet/Ents on the ObjectARX SDK) should show you how to use GetObject() on the BlockTable and the modelspace (although you will only need to open each "for read").

   Regards,

   Kean

   Reply
8. 

   Leo

   February 25, 2008 at 10:10 pm

   Hello,
   In this tutorial you created the LinkedObjectManager class in order to link 2 entities. Is there something already existing in Autocad classes (maybe ObjectARX) allowing to do the same ?

   Reply
9. 

   Kean Walmsley

   February 26, 2008 at 12:48 am

   No, there isn't, so I created a simple manager class to help with (and encapsulate) the lower-level linking functions/methods you need to call.

   Kean

   Reply
10. 

    SUBIR KUMAR DUTTA

    April 16, 2008 at 3:03 pm

    For those who want to copy paste this code and run but don't have time to clean by deleting the line numbers. Thanks to WORD VBA

    using System;
    using System.Collections;
    using System.Collections.Generic;
    using Autodesk.AutoCAD.Runtime;
    using Autodesk.AutoCAD.ApplicationServices;
    using Autodesk.AutoCAD.DatabaseServices;
    using Autodesk.AutoCAD.EditorInput;
    using Autodesk.AutoCAD.Geometry;

    [assembly:
    CommandClass(
    typeof(
    AsdkLinkingLibrary.LinkingCommands
    )
    )
    ]

    namespace AsdkLinkingLibrary
    {
    /// <summary>
    /// Utility class to manage links between objects
    /// </summary>
    public class LinkedObjectManager
    {
    Dictionary<objectid, objectidcollection=""> m_dict;

    // Constructor
    public LinkedObjectManager()
    {
    m_dict =
    new Dictionary<objectid,objectidcollection>();
    }

    // Create a bi-directional link between two objects
    public void LinkObjects(ObjectId from, ObjectId to)
    {
    CreateLink(from, to);
    CreateLink(to, from);
    }

    // Helper function to create a one-way
    // link between objects
    private void CreateLink(ObjectId from, ObjectId to)
    {
    ObjectIdCollection existingList;
    if (m_dict.TryGetValue(from, out existingList))
    {
    if (!existingList.Contains(to))
    {
    existingList.Add(to);
    m_dict.Remove(from);
    m_dict.Add(from, existingList);
    }
    }
    else
    {
    ObjectIdCollection newList =
    new ObjectIdCollection();
    newList.Add(to);
    m_dict.Add(from, newList);
    }
    }

    // Remove bi-directional links from an object
    public void RemoveLinks(ObjectId from)
    {
    ObjectIdCollection existingList;
    if (m_dict.TryGetValue(from, out existingList))
    {
    m_dict.Remove(from);
    foreach (ObjectId id in existingList)
    {
    RemoveFromList(id, from);
    }
    }
    }

    // Helper function to remove an object reference
    // from a list (assumes the overall list should
    // remain)
    private void RemoveFromList(
    ObjectId key,
    ObjectId toremove
    )
    {
    ObjectIdCollection existingList;
    if (m_dict.TryGetValue(key, out existingList))
    {
    if (existingList.Contains(toremove))
    {
    existingList.Remove(toremove);
    m_dict.Remove(key);
    m_dict.Add(key, existingList);
    }
    }
    }

    // Return the list of objects linked to
    // the one passed in
    public ObjectIdCollection GetLinkedObjects(
    ObjectId from
    )
    {
    ObjectIdCollection existingList;
    m_dict.TryGetValue(from, out existingList);
    return existingList;
    }

    // Check whether the dictionary contains
    // a particular key
    public bool Contains(ObjectId key)
    {
    return m_dict.ContainsKey(key);
    }
    }
    /// <summary>
    /// This class defines our commands and event callbacks.
    /// </summary>
    public class LinkingCommands
    {
    LinkedObjectManager m_linkManager;
    ObjectIdCollection m_entitiesToUpdate;

    public LinkingCommands()
    {
    Document doc =
    Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    db.ObjectModified +=
    new ObjectEventHandler(OnObjectModified);
    db.ObjectErased +=
    new ObjectErasedEventHandler(OnObjectErased);
    doc.CommandEnded +=
    new CommandEventHandler(OnCommandEnded);

    m_linkManager = new LinkedObjectManager();
    m_entitiesToUpdate = new ObjectIdCollection();
    }

    ~LinkingCommands()
    {
    try
    {
    Document doc =
    Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    db.ObjectModified -=
    new ObjectEventHandler(OnObjectModified);
    db.ObjectErased -=
    new ObjectErasedEventHandler(OnObjectErased);
    doc.CommandEnded +=
    new CommandEventHandler(OnCommandEnded);
    }
    catch(System.Exception)
    {
    // The document or database may no longer
    // be available on unload
    }
    }

    // Define "LINK" command
    [CommandMethod("LINK")]
    public void LinkEntities()
    {
    Document doc =
    Application.DocumentManager.MdiActiveDocument;
    Database db = doc.Database;
    Editor ed = doc.Editor;

    PromptEntityOptions opts =
    new PromptEntityOptions(
    "\nSelect first circle to link: "
    );
    opts.AllowNone = true;
    opts.SetRejectMessage(
    "\nOnly circles can be selected."
    );
    opts.AddAllowedClass(typeof(Circle), false);

    PromptEntityResult res = ed.GetEntity(opts);
    if (res.Status == PromptStatus.OK)
    {
    ObjectId from = res.ObjectId;
    opts.Message =
    "\nSelect second circle to link: ";
    res = ed.GetEntity(opts);
    if (res.Status == PromptStatus.OK)
    {
    ObjectId to = res.ObjectId;
    m_linkManager.LinkObjects(from, to);
    m_entitiesToUpdate.Add(from);
    }
    }
    }

    // Define callback for Database.ObjectModified event
    private void OnObjectModified(
    object sender, ObjectEventArgs e)
    {
    ObjectId id = e.DBObject.ObjectId;
    if (m_linkManager.Contains(id) &&
    !m_entitiesToUpdate.Contains(id))
    {
    m_entitiesToUpdate.Add(id);
    }
    }

    // Define callback for Database.ObjectErased event
    private void OnObjectErased(
    object sender, ObjectErasedEventArgs e)
    {
    if (e.Erased)
    {
    m_linkManager.RemoveLinks(e.DBObject.ObjectId);
    }
    }

    // Define callback for Document.CommandEnded event
    private void OnCommandEnded(
    object sender, CommandEventArgs e)
    {
    foreach (ObjectId id in m_entitiesToUpdate)
    {
    UpdateLinkedEntities(id);
    }
    m_entitiesToUpdate.Clear();
    }

    // Helper function for OnCommandEnded
    private void UpdateLinkedEntities(ObjectId from)
    {
    Document doc =
    Application.DocumentManager.MdiActiveDocument;
    Editor ed = doc.Editor;
    Database db = doc.Database;

    ObjectIdCollection linked =
    m_linkManager.GetLinkedObjects(from);

    Transaction tr =
    db.TransactionManager.StartTransaction();
    using (tr)
    {
    try
    {
    Point3d firstCenter;
    Point3d secondCenter;
    double firstRadius;
    double secondRadius;

    Entity ent =
    (Entity)tr.GetObject(from, OpenMode.ForRead);

    if (GetCenterAndRadius(
    ent,
    out firstCenter,
    out firstRadius
    )
    )
    {
    foreach (ObjectId to in linked)
    {
    Entity ent2 =
    (Entity)tr.GetObject(to, OpenMode.ForRead);
    if (GetCenterAndRadius(
    ent2,
    out secondCenter,
    out secondRadius
    )
    )
    {
    Vector3d vec = firstCenter - secondCenter;
    if (!vec.IsZeroLength())
    {
    // Only move the linked circle if it's not
    // already near enough
    double apart =
    vec.Length - (firstRadius + secondRadius);
    if (apart < 0.0)
    apart = -apart;

    if (apart > 0.00001)
    {
    ent2.UpgradeOpen();
    ent2.TransformBy(
    Matrix3d.Displacement(
    vec.GetNormal() * apart
    )
    );
    }
    }
    }
    }
    }
    }
    catch (System.Exception ex)
    {
    Autodesk.AutoCAD.Runtime.Exception ex2 =
    ex as Autodesk.AutoCAD.Runtime.Exception;
    if (ex2 != null &&
    ex2.ErrorStatus != ErrorStatus.WasOpenForUndo)
    {
    ed.WriteMessage(
    "\nAutoCAD exception: {0}", ex2
    );
    }
    else if (ex2 == null)
    {
    ed.WriteMessage(
    "\nSystem exception: {0}", ex
    );
    }
    }
    tr.Commit();
    }
    }

    // Helper function to get the center and radius
    // for all supported circular objects
    private bool GetCenterAndRadius(
    Entity ent,
    out Point3d center,
    out double radius
    )
    {
    // For circles it's easy...
    Circle circle = ent as Circle;
    if (circle != null)
    {
    center = circle.Center;
    radius = circle.Radius;
    return true;
    }
    else
    {
    // Throw in some empty values...
    // Returning false indicates the object
    // passed in was not useable
    center = Point3d.Origin;
    radius = 0.0;
    return false;
    }
    }
    }
    }

    Reply
11. 

    Kean Walmsley

    April 18, 2008 at 1:16 pm

    Subir - the source file is linked to for download from within the post.

    Kean

    Reply
12. 

    Cad Customizations

    July 11, 2012 at 11:22 am

    Hi Kean, In the Sample projects that come with ObjectARX SDK, there is a sample known as EventsWatcher. I had done some changes and it worked fine for ObjectAdded and ObjectErased. But for ObjectModified, I am getting a crash even if I only start a transaction and displose it with out even doing anything. Can you give me a quick tip, what I am missing here.

    private void callback_ObjectModified(object sender, ObjectEventArgs e)
    {
    WriteLine(String.Format("ObjectModified - {0} {1}", e.DBObject.ToString(), e.DBObject.Id.ToString()));

    Autodesk.AutoCAD.EditorInput.Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
    Transaction trans = ed.Document.Database.TransactionManager.StartTransaction();

    try
    {

    }
    catch (System.Exception ex)
    {

    }
    finally
    {
    trans.Dispose();
    }

    }

    Thanks

    Subir

    Reply
13. 

    Kean Walmsley

    July 31, 2012 at 10:59 am

    Hi Subir,

    Firstly, please post your questions via ADN or the AutoCAD .NET discussion group unless it's specifically related to code in one of my posts.

    Next, creating a transaction on object modified may seem innocuous, but it's actually a really bad idea. Objects are modified all the time inside AutoCAD, and you will create all kinds of problems doing this. You should queue up changes until CommandEnded (or a omparable event), and also look at StartOpenCloseTransaction(), which is safer when called from notification callbacks.

    Regards,

    Kean

    Reply
14. 

    Gustavo Barreto

    September 5, 2014 at 4:38 pm

    Hi Kean,

    I'm very interested in the code in this post. I'm trying to translate it to VB.NET, but I'm having problems with the following lines:

    126 Document doc =
    127 Application.DocumentManager.MdiActiveDocument;
    128 Database db = doc.Database;
    129 db.ObjectModified +=
    130 new ObjectEventHandler(OnObjectModified);
    131 db.ObjectErased +=
    132 new ObjectErasedEventHandler(OnObjectErased);
    133 doc.CommandEnded +=
    134 new CommandEventHandler(OnCommandEnded);

    Because the Database object doesn' have the ObjectModified property. Has it changed since you wrote this post?

    Regards,

    Gustavo Barreto

    Reply
    1. 

       Gustavo B.

       September 5, 2014 at 5:23 pm

       Hi Kean,

       I could solve it on my own. I changed the lines for:

       AddHandler db.ObjectModified, New ObjectEventHandler(AddressOf OnObjectModified)

       AddHandler db.ObjectErased, New ObjectErasedEventHandler(AddressOf OnObjectErased)

       AddHandler doc.CommandEnded, New CommandEventHandler(AddressOf OnCommandEnded)

       And it worked perfectly. Thanks anyway.

       Regards,

       Gustavo

       Reply
15. 

    Ben

    November 17, 2015 at 4:17 am

    this looks very very interesting 🙂

    Reply