Fix #342: better async thumbnail loading

QuickLook.Plugin/QuickLook.Plugin.PDFViewer/PdfDocumentWrapper.cs

@@ -0,0 +1,58 @@
+// Copyright © 2018 Paddy Xu
+// 
+// This file is part of QuickLook program.
+// 
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System;
+using System.IO;
+using PdfiumViewer;
+
+namespace QuickLook.Plugin.PDFViewer
+{
+    public class PdfDocumentWrapper : IDisposable
+    {
+        public PdfDocumentWrapper(Stream stream)
+        {
+            PdfStream = new MemoryStream((int) stream.Length);
+            stream.CopyTo(PdfStream);
+
+            PdfDocument = PdfDocument.Load(PdfStream);
+        }
+
+        public PdfDocument PdfDocument { get; private set; }
+
+        public MemoryStream PdfStream { get; private set; }
+
+        public void Dispose()
+        {
+            PdfDocument.Dispose();
+            PdfDocument = null;
+            PdfStream.Dispose();
+            PdfStream = null;
+        }
+
+        public void Refresh()
+        {
+            var oldD = PdfDocument;
+
+            PdfStream.Position = 0;
+            var newObj = new PdfDocumentWrapper(PdfStream);
+            PdfDocument = newObj.PdfDocument;
+            PdfStream = newObj.PdfStream;
+
+            oldD.Dispose();
+        }
+    }
+}