better and faster window resize; Add "AllowsTransparency" to plugin interface; Use IPreviewHandler for Office files

QuickLook.Plugin/QuickLook.Plugin.IPreviewHandlers/PreviewHandlerHost.cs

@@ -0,0 +1,157 @@
+// Preview Handlers Revisted
+// Bradley Smith - 2010/09/17, updated 2013/10/14
+
+using System;
+using System.ComponentModel;
+using System.Drawing;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Windows.Forms;
+using Microsoft.Win32;
+
+namespace QuickLook.Plugin.IPreviewHandlers
+{
+    /// <summary>
+    ///     A Windows Forms host for Preview Handlers.
+    /// </summary>
+    public class PreviewHandlerHost : Control
+    {
+        /// <summary>
+        ///     The GUID for the IShellItem interface.
+        /// </summary>
+        internal const string GuidIshellitem = "43826d1e-e718-42ee-bc55-a1e261c37bfe";
+
+        private IPreviewHandler _mCurrentPreviewHandler;
+
+        /// <summary>
+        ///     Initialialises a new instance of the PreviewHandlerHost class.
+        /// </summary>
+        public PreviewHandlerHost()
+        {
+            Size = new Size(320, 240);
+        }
+
+        /// <summary>
+        ///     Gets the GUID of the current preview handler.
+        /// </summary>
+        [Browsable(false)]
+        [ReadOnly(true)]
+        public Guid CurrentPreviewHandler { get; private set; } = Guid.Empty;
+
+        /// <summary>
+        ///     Releases the unmanaged resources used by the PreviewHandlerHost and optionally releases the managed resources.
+        /// </summary>
+        /// <param name="disposing"></param>
+        protected override void Dispose(bool disposing)
+        {
+            UnloadPreviewHandler();
+
+            if (_mCurrentPreviewHandler != null)
+            {
+                Marshal.FinalReleaseComObject(_mCurrentPreviewHandler);
+                _mCurrentPreviewHandler = null;
+                GC.Collect();
+            }
+
+            base.Dispose(disposing);
+        }
+
+        /// <summary>
+        ///     Returns the GUID of the preview handler associated with the specified file.
+        /// </summary>
+        /// <param name="filename"></param>
+        /// <returns></returns>
+        private Guid GetPreviewHandlerGUID(string filename)
+        {
+            // open the registry key corresponding to the file extension
+            var ext = Registry.ClassesRoot.OpenSubKey(Path.GetExtension(filename));
+            if (ext != null)
+            {
+                // open the key that indicates the GUID of the preview handler type
+                var test = ext.OpenSubKey("shellex\\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
+                if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
+
+                // sometimes preview handlers are declared on key for the class
+                var className = Convert.ToString(ext.GetValue(null));
+                if (className != null)
+                {
+                    test = Registry.ClassesRoot.OpenSubKey(
+                        className + "\\shellex\\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
+                    if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
+                }
+            }
+
+            return Guid.Empty;
+        }
+
+        /// <summary>
+        ///     Resizes the hosted preview handler when this PreviewHandlerHost is resized.
+        /// </summary>
+        /// <param name="e"></param>
+        protected override void OnResize(EventArgs e)
+        {
+            base.OnResize(e);
+
+            var r = ClientRectangle;
+            _mCurrentPreviewHandler?.SetRect(ref r);
+        }
+
+        /// <summary>
+        ///     Opens the specified file using the appropriate preview handler and displays the result in this PreviewHandlerHost.
+        /// </summary>
+        /// <param name="path"></param>
+        /// <returns></returns>
+        public bool Open(string path)
+        {
+            UnloadPreviewHandler();
+
+            if (string.IsNullOrEmpty(path))
+                return false;
+
+            // try to get GUID for the preview handler
+            var guid = GetPreviewHandlerGUID(path);
+
+            if (guid == Guid.Empty)
+                return false;
+
+            CurrentPreviewHandler = guid;
+            var o = Activator.CreateInstance(Type.GetTypeFromCLSID(CurrentPreviewHandler, true));
+
+            var fileInit = o as IInitializeWithFile;
+
+            if (fileInit == null)
+                return false;
+
+            fileInit.Initialize(path, 0);
+            _mCurrentPreviewHandler = o as IPreviewHandler;
+            if (_mCurrentPreviewHandler == null)
+                return false;
+
+            // bind the preview handler to the control's bounds and preview the content
+            var r = ClientRectangle;
+            _mCurrentPreviewHandler.SetWindow(Handle, ref r);
+            _mCurrentPreviewHandler.DoPreview();
+
+            return true;
+        }
+
+        /// <summary>
+        ///     Unloads the preview handler hosted in this PreviewHandlerHost and closes the file stream.
+        /// </summary>
+        public void UnloadPreviewHandler()
+        {
+            try
+            {
+                _mCurrentPreviewHandler?.Unload();
+            }
+            catch (Exception)
+            {
+                // ignored
+            }
+        }
+    }
+
+    #region COM Interop
+
+    #endregion
+}