'原文：http://through-the-interface.typepad.com/through_the_interface/2011/11/gen ... -blocks-in-an-autocad-drawing-using-net.html
'VB.Net翻译转换 田草博客 www.tiancao.net
Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.EditorInput
Imports Autodesk.AutoCAD.Geometry
Imports Autodesk.AutoCAD.Runtime
Imports System.IO
Namespace BlockPreviews
    Public Class Commands
        <CommandMethod("GBP", CommandFlags.Session)> _
        Public Shared Sub GenerateBlockPreviews()
            Dim ed As Editor = Application.DocumentManager.MdiActiveDocument.Editor
            Dim res As PromptFileNameResult = ed.GetFileNameForOpen("选择你要生成预览图像的文件:")
            If res.Status <> PromptStatus.OK Then
                Return
            End If
            Dim doc As Document = Nothing
            Try
                doc = Application.DocumentManager.Open(res.StringResult, False)
            Catch
                ed.WriteMessage(vbLf & "图形文件无效.")
                Return
            End Try
            Dim db As Database = doc.Database
            Dim path As String = System.IO.Path.GetDirectoryName(res.StringResult), name As String = System.IO.Path.GetFileName(res.StringResult), iconPath As String = path + "\" + name + " icons"
            Dim numIcons As Integer = 0
            Dim tr As Transaction = doc.TransactionManager.StartTransaction()
            Using tr
                Dim table As BlockTable = CType(tr.GetObject(db.BlockTableId, OpenMode.ForRead), BlockTable)
                For Each blkId As ObjectId In table
                    Dim blk As BlockTableRecord = CType(tr.GetObject(blkId, OpenMode.ForRead), BlockTableRecord)
                    ' 忽略布局和匿名块
                    If blk.IsLayout OrElse blk.IsAnonymous Then
                        Continue For
                    End If
                    ' 当缩略图不在时,生成缩略图
                    If blk.PreviewIcon Is Nothing Then
                        Dim ActiveDocument As Object = doc.AcadDocument
                        Dim data As Object() = {"_.BLOCKICON " + blk.Name + vbLf}
                        ActiveDocument.[GetType]().InvokeMember("SendCommand", System.Reflection.BindingFlags.InvokeMethod, Nothing, ActiveDocument, data)
                    End If
                    ' 现在所有块都有了缩略图
                    If blk.PreviewIcon IsNot Nothing Then
                        ' 创建一个输出文件夹
                        If Not Directory.Exists(iconPath) Then
                            Directory.CreateDirectory(iconPath)
                        End If
                        ' 保存缩略图至文件夹
                        blk.PreviewIcon.Save(iconPath + "\" + blk.Name + ".bmp")
                        ' 图标计数器加1
                        System.Math.Max(System.Threading.Interlocked.Increment(numIcons), numIcons - 1)
                    End If
                Next
                tr.Commit()
            End Using
            doc.CloseAndDiscard()
            ed.WriteMessage(vbLf & "{0} block icons saved to ""{1}"".", numIcons, iconPath)
        End Sub
    End Class
End Namespace