Per-document Data in AutoCAD .NET Applications - Part 2 - Through the Interface_GOOD

Per-document data in AutoCAD .NET applications - Part 2 - Through the Interface

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Per-document data in AutoCAD .NET applications - Part 1 | Main | A quickVisual Studio tip - automatically implement interfaces in C#

October 19, 2006

Per-document data in AutoCAD .NET applications - Part 2This entry completes the series of posts about per-document data. Here are theprevious entries:

Some background to AutoCAD's MDI implementation and per-document dataPer-document data in ObjectARXPer-document data in AutoCAD .NET applications - Part 1

Document.UserData

Now let's take a look at a second technique in .NET for storing transient (non-persisted) data with an AutoCAD document, the UserData property. The managedframework for AutoCAD associates a hash table with each document, which canbe accessed using the UserData property. Hash tables are a great way to storeand access data quickly: each object you store in a hash table is associated witha particular key, or lookup value. You then use this key to get at the data you'vestored in the hash table.

The UserData property returns an object of the standard .NET class,System.Collections.Hashtable, so its advised to look on MSDN for furtherexamples of usage.

I've written some code to demonstrate how you might store and access per-document data in the UserData property. The below C# code declares andimplements a simple class called MyData to store custom data, and then twocommands that store data in and use data from the UserData hash table.

The inc command checks whether theres an object under a particularkey, and if not, it creates and adds a MyData object. It then goes on toincrement the integer value stored in that object (and therefore in thehash table)

The bogus command has some fun with the hash table, storing abogus object (a Point2D object) in the place where the "inc" commandexpects to find a MyData object. This can only be run on a freshdrawing one that has not had inc executed otherwise there willalready be an object stored in the hash table

Here's the code:

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

[assembly: CommandClass(typeof(CommandClasses.UserDataClass))]

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namespace CommandClasses{ public class UserDataClass { // Specify a key under which we want // to store our custom data const string myKey = "AsdkData";

// Define a class for our custom data public class MyData { public int counter; public MyData() { counter = 0; } }

[Autodesk.AutoCAD.Runtime.CommandMethod("inc")] public static void increment() { Document doc = Application.DocumentManager.MdiActiveDocument; Editor ed = doc.Editor; Hashtable ud = doc.UserData; MyData md;

md = ud[myKey] as MyData; if (md == null) { object obj = ud[myKey]; if (obj == null) { // MyData object not found - first time run md = new MyData(); ud.Add(myKey, md); } else { // Found something different instead ed.WriteMessage( "Found an object of type \"" + obj.GetType().ToString() + "\" instead of MyData."); } } if (md != null) { ed.WriteMessage("\nCounter value is: " + md.counter++); } } [Autodesk.AutoCAD.Runtime.CommandMethod("bogus")] public static void addBogus() { Document doc = Application.DocumentManager.MdiActiveDocument; Editor ed = doc.Editor; Hashtable ud = doc.UserData; Point2d pt = new Point2d(); try {

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ud.Add(myKey, pt); } catch { ed.WriteMessage( "\nCould not add bogus object at \"" + myKey + "\", must be something there already."); } } }}

Now let's take a look at that running:

[From first drawing...]

Command: incCounter value is: 0Command: incCounter value is: 1Command: incCounter value is: 2Command: incCounter value is: 3Command: new

[From second drawing...]

Command: incCounter value is: 0Command: incCounter value is: 1Command: incCounter value is: 2Command: bogusCould not add bogus object at "AsdkData", must be something therealready.Command: new

[From third drawing...]

Command: bogusCommand: incFound an object of type "Autodesk.AutoCAD.Geometry.Point2d" instead ofMyData.

Posted at 04:42 PM in AutoCAD, AutoCAD .NET | Permalink

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Thanks for your great article,Kean.For C++,you give the Falsely MDI-Aware Versionexample.

csharpbird said...

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Reply October 19, 2006 at 07:46 PM

What about .NET?


Thanks, csharpbird.If you take a look at the previous entry (Part 1), you cansee the "glob" command implementation... this could beconsidered a "Falsely MDI-Aware" command, if thecommand was supposed to be considering the countervariable to be local for each document.

Kean said...


Thanks, Kean! Your's last three articles is very useful!

Alexander Rivilis said...


Great couple of articles Kean.This is always a subject developers are unaware ofwhen developing ObjectARX applications and it wouldhappen with .NET too.

Thanks, Fernando.

Fernando Malard said...

Reply May 16, 2008 at 07:09 PM

hi kean,

are you aware of the difference between static andinstance variables in an AutoCAD .NET applicationcommand class? If you create static variables (and astatic command method), they exist only once. If youcreate instance variables (and a non-static commandmethod), a new instance of the class is instantiated foreach AutoCAD document. This automatically generatesand manages per-document data, with no need for anywork at all from your side. I have a nice sampledemonstrating this, if you like.

cheers

jeremy

jeremy said...

Hi Jeremy,

Yes, I am - the previous post covered that.

The reason I used this approach in another recent postis actually that sometimes the class instances you

Kean said...

More...



Reply May 17, 2008 at 10:56 AM

receive automatically are not the ones you expect -particularly when implementing event handlers(presumably it's because you're in the applicationcontext rather than being in a particular document'scontext, depending). So I actually find UserData to bemore predictable and therefore dependable.

Cheers,

Kean

Reply June 08, 2009 at 05:46 PM

Hi,KeanYou've said"I've written some code to demonstrate how you mightstore and access per-document data in the UserDataproperty"Where can I find these code? Thank u.

hhhwjb

hhhwjb said...


hhhwjb - it's the C# code in this post.

Kean

Kean Walmsley said...

Reply June 09, 2009 at 02:38 AM

Hi,KeanThank u for ur answer.I test this code, when I close the document,theUserData lost. How can I save the UserData togetherwith my documentation?Thank u in advance.

hhhwjb said...

Reply June 09, 2009 at 08:13 AM

This example does not persist data in the DWG file: itjust associates it with the document for runtime access.If you need to persist data then you'll probably want touse XRecords to do so (search this blog to findexamples).

Kean

Kean Walmsley said...

Hi Kean,I came across this article when i was

Matus said in reply to Kean Walmsley...



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Reply January 13, 2011 at 04:55 PM

searching for a way to store custom classesin AutoCAD drawing.I thought i found the answear until i realised,that this data is not persistent.On the other hand XRecord can only storeResultBuffer type in his Data property andDBDictionary can only store classes derivedfrom the DBObject class. Or am I wrong?

What is the best way to store custom classesid drawings persistently?

Matus

Reply January 13, 2011 at 05:06 PM

Hi Matus,

Regarding your last question (which may alsorespond to your others), It depends:

Xdata for smallish amounts (meaning up toabout 4K, as a rule of thumb... there's ashared 16K limit per chunk of Xdata, if I recallcorrectly).

Xrecords in extension dictionaries (or centrallyin the named objects dictionary) for largeramounts.

ResultBuffers are actually reasonably flexible,if you implement them properly.

Regards,

Kean

Kean Walmsley said in reply to Matus...


Thank u very much.

hhhwjb said...

Reply December 14, 2012 at 03:13 PM

Thanks Kean, it is still relevant in 2012.RegardsCraig

Craig Nicholas said...



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