How to determine if entity is a block?

[edweberg]

Greetings,

I'm writing an app in VB.NET.  In a small part of the code I'm working on, I need to examine each entity in a drawing and determine whether it is a block, and if it is not a block, erase it from the drawing. 

Here's a snip from the part of the code in question.  I can't find an example of how to determine if an entity is a block or not.  Can anyone help me get started filling in the green part below.  Thank you for any suggestions.

Erik

Dim myEd As Editor = DocumentManager.MdiActiveDocument.Editor

Dim myPSR As PromptSelectionResult = myEd.SelectAll

 If myPSR.Status = PromptStatus.OK Then

   Dim mySS As SelectionSet= myPSR.Value

   ForEach mySelObj As SelectedObject In mySS

   Dim myEnt As Entity = mySelObj.ObjectId.GetObject(OpenMode.ForWrite)

'If my Entity is not a block or nested within a block, erase it...

   Next

 EndIf

[hgasty1001 · Accepted solution]

Hi,

Instead to test each entity, a better aproach could be to select all entities that do not acomplish the criteria, in this case all entities that are not block references (Block Inserts), this is as easy as using a filter with the "not" operator:

Public Sub DeleteNoBlocksReferences()
        Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument
        Dim acCurDb As Database = acDoc.Database
        Dim ret As SelectionSet

        Using acTrans As Transaction = acCurDb.TransactionManager.StartTransaction()
            Dim acTypValAr(2) As TypedValue

            acTypValAr.SetValue(New TypedValue(DxfCode.Operator, "<not"), 0)
            acTypValAr.SetValue(New TypedValue(DxfCode.Start, "INSERT"), 1)
            acTypValAr.SetValue(New TypedValue(DxfCode.Operator, "not>"), 2)

            Dim acSelFtr As SelectionFilter = New SelectionFilter(acTypValAr)
            Dim acSSPrompt As PromptSelectionResult
            Dim ed As Editor = Application.DocumentManager.MdiActiveDocument.Editor

            acSSPrompt = ed.SelectAll(acSelFtr)

            If acSSPrompt.Status = PromptStatus.OK Then
                ret = acSSPrompt.Value
                Dim objids() As ObjectId
                objids = ret.GetObjectIds
                For Each objid As ObjectId In objids
                    Dim obj As DBObject = acTrans.GetObject(objid, OpenMode.ForWrite)
                    obj.Erase()
                Next
            End If
            acTrans.Commit()
        End Using
    End Sub

    <CommandMethod("ENOBLK")> _
    Public Sub enoblk()
        DeleteNoBlocksReferences()
    End Sub

Gaston Nunez

[mzakiralam]

you can also try like below:

If Typeof myEnt is BlockReference

'do as you need

EndIf

[architectOfIdeas]

I support the method of filtering the selection that Gaston has suggested. It's a bit more authoring (and it might take a bit to understand how the .Operators work) but it is an explicit approach that can be easily modified to include specific properties later. Although, it might make more sense when dealing with a large file or when including more function than just erasing the block reference.

If Not TypeOf acObject is BlockReference does what you need though, go for it!

[dgorsman]

Do selection sets still work when the document isn't active e.g. using a side database?

[_gile · Accepted solution]

hi,

No, you can only use selection sets if the document is opened in the editor (all selection set methods are instance methods of the Editor class).

Using a side database, you'd have to iterate the model (and/or paper) space BlockTableRecord and filter the contained entity.

        private void EraseAllButBlocks(Database db)
        {
            RXClass blockClass = RXClass.GetClass(typeof(BlockReference));
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                BlockTableRecord modelSpace = (BlockTableRecord)tr.GetObject(
                    SymbolUtilityServices.GetBlockModelSpaceId(db), OpenMode.ForRead);
                foreach (ObjectId id in modelSpace)
                {
                    if (id.ObjectClass != blockClass)
                    {
                        Entity ent = (Entity)tr.GetObject(id, OpenMode.ForWrite);
                        try { ent.Erase(); }
                        catch { }
                    }
                }
                tr.Commit();
            }
        }

[edweberg]

Thank you for all the replies.  I got the solution I needed and much more.

Erik

[ThomasLongnecker]

Just in case someone is looking for the answer to the original question.  I found two ways (there maybe more) of determining if an entity is a block reference or not.

Given the code in the original post the following two technique should work

If MySelObj.ObjectId.ObjectClass.DxfName = "INSERT" Then

If MyEnt.GetType.Namespace = "Reference" Then

Thomas

[kdub_nz]

Thomas,

I think you'll find the  RXClass comparison ( as demonstrated by gile) more efficient.

[ThomasLongnecker]

Kerry,

I am pretty new to programming AutoCAD with .NET and would appricate the opertunity to learn from you.

Can you give a brief explanaiton what would make the RXClass comparison "more efficiate" then the original and later posted VB comparison?

Thanks,
Thomas