AutoCAD.Net/C#.Net QQ群:193522571 previewicon生成的块图标太小，CMLContentSearchPreviews生成大的图片

由于CMLContentSearchPreviews方法是AutoCAD2014中才加入的，所以只能应用于2014及以后版本，可惜啊！

using System.IO;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.Windows.Data;
namespace BlockPreviews
{
    public class Commands
    {
        [CommandMethod("GBP", CommandFlags.Session)]
        public static void GenerateBlockPreviews()
        {
            var ed = Application.DocumentManager.MdiActiveDocument.Editor;
            var res = ed.GetFileNameForOpen("Select file for which to generate previews");
            if (res.Status != PromptStatus.OK)
                return;
            string dwgname = res.StringResult;
            Document doc = null;
            try
            {
                doc = Application.DocumentManager.Open(dwgname, false);
            }
            catch
            {
                ed.WriteMessage("
Unable to read drawing.");
                return;
            }
            var db = doc.Database;
            string path = Path.GetDirectoryName(dwgname),
                   name = Path.GetFileName(dwgname),
                   iconPath = path + "\" + name + " icons";
            int numIcons = 0;
            using (var tr = doc.TransactionManager.StartTransaction())
            {
                var bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);

                foreach (ObjectId btrId in bt)
                {
                    var btr = (BlockTableRecord)tr.GetObject(btrId, OpenMode.ForRead);
                    // Ignore layouts and anonymous blocks
                    if (btr.IsLayout || btr.IsAnonymous)
                        continue;
                    // Attempt to generate an icon, where one doesn't exist
                    if (btr.PreviewIcon == null)
                    {
                        object ActiveDocument = doc.GetAcadDocument();
                        object[] data = { "_.BLOCKICON " + btr.Name + "
" };
                        ActiveDocument.GetType().InvokeMember(
                          "SendCommand",
                          System.Reflection.BindingFlags.InvokeMethod,
                          null, ActiveDocument, data
                        );
                    }

                    // Hopefully we now have an icon

                    if (btr.PreviewIcon != null)
                    {
                        // Create the output directory, if it isn't yet there

                        if (!Directory.Exists(iconPath))
                            Directory.CreateDirectory(iconPath);

                        var fname = iconPath + "\" + btr.Name + ".bmp";

                        // Delete the image if it already exists

                        if (File.Exists(fname))
                            File.Delete(fname);

                        // Save the icon to our out directory

                        btr.PreviewIcon.Save(fname);

                        // Increment our icon counter

                        numIcons++;
                    }
                }
                tr.Commit();
            }
            doc.CloseAndDiscard();

            ed.WriteMessage("
{0} block icons saved to "{1}".", numIcons, iconPath);
        }

        [CommandMethod("GBP2")]
        public static void GenerateBlockPreviews2()
        {
            Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;

            PromptFileNameResult res = ed.GetFileNameForOpen("Select file for which to generate previews");
            if (res.Status != PromptStatus.OK)
                return;

            string dwgname = res.StringResult;
            int numIcons;
            string iconPath;

            // We don't need a document for access to the BlockTable

            using (var db = new Database(false, true))
            {
                try
                {
                    db.ReadDwgFile(
                      dwgname,
                      FileOpenMode.OpenForReadAndReadShare,
                      true,
                      ""
                    );
                }
                catch
                {
                    ed.WriteMessage("
Unable to read drawing.");
                    return;
                }

                var path = Path.GetDirectoryName(dwgname);
                var name = Path.GetFileName(dwgname);
                iconPath = path + "\" + name + " icons";

                using (var tr = db.TransactionManager.StartTransaction())
                {
                    var bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);
                    numIcons = ExtractThumbnails(iconPath, tr, bt);
                    tr.Commit();
                }
            }

            ed.WriteMessage("
{0} block icons saved to "{1}".", numIcons, iconPath);
        }

        [CommandMethod("GBPC")]
        public static void GenerateCurrentBlockPreviews()
        {
            var doc = Application.DocumentManager.MdiActiveDocument;
            var ed = doc.Editor;
            var db = doc.Database;

            var path = (string)Application.GetSystemVariable("DWGPREFIX");
            var name = (string)Application.GetSystemVariable("DWGNAME");
            var iconPath = path + name + " icons";

            using (var tr = doc.TransactionManager.StartTransaction())
            {
                var bt = (BlockTable)tr.GetObject(db.BlockTableId, OpenMode.ForRead);
                int numIcons = ExtractThumbnails(iconPath, tr, bt);
                tr.Commit();
                ed.WriteMessage("
{0} block icons saved to "{1}".", numIcons, iconPath);
            }
        }

        private static int ExtractThumbnails(string iconPath, Transaction tr, BlockTable bt)
        {
            int numIcons = 0;
            foreach (ObjectId btrId in bt)
            {
                var btr = (BlockTableRecord)tr.GetObject(btrId, OpenMode.ForRead);

                // Ignore layouts and anonymous blocks
                if (btr.IsLayout || btr.IsAnonymous)
                    continue;
                // Attempt to generate an icon, where one doesn't exist
                {
                    // Create the output directory, if it isn't yet there
                    if (!Directory.Exists(iconPath))
                        Directory.CreateDirectory(iconPath);
                    // Save the icon to our out directory
                    var imgsrc = CMLContentSearchPreviews.GetBlockTRThumbnail(btr);
                    var bmp = ImageSourceToGDI(imgsrc as System.Windows.Media.Imaging.BitmapSource);
                    var fname = iconPath + "\" + btr.Name + ".bmp";
                    if (File.Exists(fname))
                        File.Delete(fname);
                    bmp.Save(fname);
                    // Increment our icon counter
                    numIcons++;
                }
            }
            return numIcons;
        }

        // Helper function to generate an Image from a BitmapSource

        private static System.Drawing.Image ImageSourceToGDI(System.Windows.Media.Imaging.BitmapSource src
        )
        {
            var ms = new MemoryStream();
            var encoder = new System.Windows.Media.Imaging.BmpBitmapEncoder();
            encoder.Frames.Add(System.Windows.Media.Imaging.BitmapFrame.Create(src));
            encoder.Save(ms);
            ms.Flush();
            return System.Drawing.Image.FromStream(ms);
        }
    }
}