Added experimental option to sync events to UI thread.

NTwain/MessageLoop.cs

@@ -15,7 +15,6 @@ namespace NTwain
     /// </summary>
     class MessageLoop
     {
-        // mostly wraps around a dispatcher?
         static MessageLoop _instance = new MessageLoop();
         public static MessageLoop Instance { get { return _instance; } }
 
@@ -24,6 +23,7 @@ namespace NTwain
         HwndSource _dummyWindow;
 
         private MessageLoop() { }
+
         public void EnsureStarted()
         {
             if (!_started)
@@ -42,8 +42,9 @@ namespace NTwain
                         // CS_NOCLOSE, WS_DISABLED, and WS_EX_NOACTIVATE
                         _dummyWindow = new HwndSource(0x0200, 0x8000000, 0x8000000, 0, 0, "NTWAIN_LOOPER", IntPtr.Zero);
                     }
-                    hack.Set();
+                    hack.Set(); 
                     Dispatcher.Run();
+                    _started = false;
                 }));
                 loopThread.IsBackground = true;
                 loopThread.SetApartmentState(ApartmentState.STA);

NTwain/Properties/VersionInfo.cs

@@ -14,6 +14,6 @@ namespace NTwain
         // keep this same in majors releases
         public const string Release = "0.11.0.0";
         // change this for each nuget release
-        public const string Build = "0.11.1";
+        public const string Build = "0.11.2";
     }
 }

NTwain/TwainSession.cs

@@ -65,6 +65,16 @@ namespace NTwain
             }
         }
 
+        /// <summary>
+        /// EXPERIMENTAL. Gets or sets the optional synchronization context.
+        /// This allows events to be raised on the thread
+        /// associated with the context.
+        /// </summary>
+        /// <value>
+        /// The synchronization context.
+        /// </value>
+        public SynchronizationContext SynchronizationContext { get; set; }
+
 
         #region ITwainStateInternal Members
 
@@ -88,7 +98,7 @@ namespace NTwain
             if (notifyChange)
             {
                 RaisePropertyChanged("State");
-                OnStateChanged();
+                SafeAsyncSyncableRaiseOnEvent(OnStateChanged, StateChanged);
             }
         }
 
@@ -101,7 +111,7 @@ namespace NTwain
         {
             SourceId = sourceId;
             RaisePropertyChanged("SourceId");
-            OnSourceChanged();
+            SafeAsyncSyncableRaiseOnEvent(OnSourceChanged, SourceChanged);
         }
 
         #endregion
@@ -132,7 +142,7 @@ namespace NTwain
                 {
                     _state = value;
                     RaisePropertyChanged("State");
-                    OnStateChanged();
+                    SafeAsyncSyncableRaiseOnEvent(OnStateChanged, StateChanged);
                 }
             }
         }
@@ -195,8 +205,27 @@ namespace NTwain
         /// <param name="propertyName">Name of the property.</param>
         protected void RaisePropertyChanged(string propertyName)
         {
-            var hand = PropertyChanged;
+            if (SynchronizationContext == null)
-            if (hand != null) { hand(this, new PropertyChangedEventArgs(propertyName)); }
+            {
+                try
+                {
+                    var hand = PropertyChanged;
+                    if (hand != null) { hand(this, new PropertyChangedEventArgs(propertyName)); }
+                }
+                catch { }
+            }
+            else
+            {
+                SynchronizationContext.Post(o =>
+                {
+                    try
+                    {
+                        var hand = PropertyChanged;
+                        if (hand != null) { hand(this, new PropertyChangedEventArgs(propertyName)); }
+                    }
+                    catch { }
+                }, null);
+            }
         }
 
         #endregion
@@ -389,7 +418,7 @@ namespace NTwain
                     {
                         _callbackObj = null;
                     }
-                    OnSourceDisabled();
+                    SafeAsyncSyncableRaiseOnEvent(OnSourceDisabled, SourceDisabled);
                 }
             });
             return rc;
@@ -483,123 +512,108 @@ namespace NTwain
         public event EventHandler<TransferErrorEventArgs> TransferError;
 
         /// <summary>
-        /// Called when <see cref="State"/> changed
+        /// Raises event and if applicable marshal it synchronously to the <see cref="SynchronizationContext" /> thread.
-        /// and raises the <see cref="StateChanged" /> event.
         /// </summary>
-        protected virtual void OnStateChanged()
+        /// <typeparam name="TEventArgs">The type of the event arguments.</typeparam>
+        /// <param name="onEventFunc">The on event function.</param>
+        /// <param name="handler">The handler.</param>
+        /// <param name="e">The <see cref="TEventArgs"/> instance containing the event data.</param>
+        void SafeSyncableRaiseOnEvent<TEventArgs>(Action<TEventArgs> onEventFunc, EventHandler<TEventArgs> handler, TEventArgs e) where TEventArgs : EventArgs
         {
-            var hand = StateChanged;
+            var syncer = SynchronizationContext;
-            if (hand != null)
+            if (syncer == null)
             {
                 try
                 {
-                    hand(this, EventArgs.Empty);
+                    onEventFunc(e);
+                    if (handler != null) { handler(this, e); }
                 }
                 catch { }
             }
+            else
+            {
+                syncer.Send(o =>
+                {
+                    try
+                    {
+                        onEventFunc(e);
+                        if (handler != null) { handler(this, e); }
+                    }
+                    catch { }
+                }, null);
+            }
         }
 
         /// <summary>
-        /// Called when <see cref="SourceId"/> changed
+        /// Raises event and if applicable marshal it asynchronously to the <see cref="SynchronizationContext"/> thread.
-        /// and raises the <see cref="SourceChanged" /> event.
         /// </summary>
-        protected virtual void OnSourceChanged()
+        /// <param name="onEventFunc">The on event function.</param>
+        /// <param name="handler">The handler.</param>
+        void SafeAsyncSyncableRaiseOnEvent(Action onEventFunc, EventHandler handler)
         {
-            var hand = SourceChanged;
+            var syncer = SynchronizationContext;
-            if (hand != null)
+            if (syncer == null)
             {
                 try
                 {
-                    hand(this, EventArgs.Empty);
+                    onEventFunc();
+                    if (handler != null) { handler(this, EventArgs.Empty); }
                 }
                 catch { }
             }
+            else
+            {
+                syncer.Post(o =>
+                {
+                    try
+                    {
+                        onEventFunc();
+                        if (handler != null) { handler(this, EventArgs.Empty); }
+                    }
+                    catch { }
+                }, null);
+            }
         }
 
         /// <summary>
-        /// Called when source has been disabled (back to state 4)
+        /// Called when <see cref="State"/> changed.
-        /// and raises the <see cref="SourceDisabled" /> event.
         /// </summary>
-        protected virtual void OnSourceDisabled()
+        protected virtual void OnStateChanged() { }
-        {
-            var hand = SourceDisabled;
-            if (hand != null)
-            {
-                try
-                {
-                    hand(this, EventArgs.Empty);
-                }
-                catch { }
-            }
-        }
 
         /// <summary>
-        /// Raises the <see cref="E:DeviceEvent" /> event.
+        /// Called when <see cref="SourceId"/> changed.
+        /// </summary>
+        protected virtual void OnSourceChanged() { }
+
+        /// <summary>
+        /// Called when source has been disabled (back to state 4).
+        /// </summary>
+        protected virtual void OnSourceDisabled() { }
+
+        /// <summary>
+        /// Called when the source has generated an event.
         /// </summary>
         /// <param name="e">The <see cref="DeviceEventArgs"/> instance containing the event data.</param>
-        protected virtual void OnDeviceEvent(DeviceEventArgs e)
+        protected virtual void OnDeviceEvent(DeviceEventArgs e) { }
-        {
-            var hand = DeviceEvent;
-            if (hand != null)
-            {
-                try
-                {
-                    hand(this, e);
-                }
-                catch { }
-            }
-        }
 
         /// <summary>
-        /// Raises the <see cref="E:TransferReady" /> event.
+        /// Called when a data transfer is ready.
         /// </summary>
         /// <param name="e">The <see cref="TransferReadyEventArgs"/> instance containing the event data.</param>
-        protected virtual void OnTransferReady(TransferReadyEventArgs e)
+        protected virtual void OnTransferReady(TransferReadyEventArgs e) { }
-        {
-            var hand = TransferReady;
-            if (hand != null)
-            {
-                try
-                {
-                    hand(this, e);
-                }
-                catch { }
-            }
-        }
 
         /// <summary>
-        /// Raises the <see cref="E:DataTransferred" /> event.
+        /// Called when data has been transferred.
         /// </summary>
         /// <param name="e">The <see cref="DataTransferredEventArgs"/> instance containing the event data.</param>
-        protected virtual void OnDataTransferred(DataTransferredEventArgs e)
+        protected virtual void OnDataTransferred(DataTransferredEventArgs e) { }
-        {
-            var hand = DataTransferred;
-            if (hand != null)
-            {
-                try
-                {
-                    hand(this, e);
-                }
-                catch { }
-            }
-        }
 
         /// <summary>
-        /// Raises the <see cref="E:TransferError" /> event.
+        /// Called when an error has been encountered during transfer.
         /// </summary>
         /// <param name="e">The <see cref="TransferErrorEventArgs"/> instance containing the event data.</param>
-        protected virtual void OnTransferError(TransferErrorEventArgs e)
+        protected virtual void OnTransferError(TransferErrorEventArgs e) { }
-        {
+
-            var hand = TransferError;
-            if (hand != null)
-            {
-                try
-                {
-                    hand(this, e);
-                }
-                catch { }
-            }
-        }
         #endregion
 
         #region TWAIN logic during xfer work
@@ -671,7 +685,7 @@ namespace NTwain
                     var rc = DGControl.DeviceEvent.Get(out de);
                     if (rc == ReturnCode.Success)
                     {
-                        OnDeviceEvent(new DeviceEventArgs(de));
+                        SafeSyncableRaiseOnEvent(OnDeviceEvent, DeviceEvent, new DeviceEventArgs(de));
                     }
                     break;
                 case Message.CloseDSReq:
@@ -726,7 +740,7 @@ namespace NTwain
                     EndOfJob = pending.EndOfJob == 0
                 };
 
-                OnTransferReady(preXferArgs);
+                SafeSyncableRaiseOnEvent(OnTransferReady, TransferReady, preXferArgs);
 
                 #endregion
 
@@ -805,16 +819,17 @@ namespace NTwain
                     {
                         lockedPtr = MemoryManager.Instance.Lock(dataPtr);
                     }
-                    OnDataTransferred(new DataTransferredEventArgs { NativeData = lockedPtr });
+
+                    SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { NativeData = lockedPtr });
                 }
                 else
                 {
-                    OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                    SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
                 }
             }
             catch (Exception ex)
             {
-                OnTransferError(new TransferErrorEventArgs { Exception = ex });
+                SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { Exception = ex });
             }
             finally
             {
@@ -845,11 +860,11 @@ namespace NTwain
             var xrc = DGAudio.AudioFileXfer.Get();
             if (xrc == ReturnCode.XferDone)
             {
-                OnDataTransferred(new DataTransferredEventArgs { FileDataPath = filePath });
+                SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { FileDataPath = filePath });
             }
             else
             {
-                OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
             }
         }
 
@@ -876,16 +891,16 @@ namespace NTwain
                     {
                         lockedPtr = MemoryManager.Instance.Lock(dataPtr);
                     }
-                    OnDataTransferred(new DataTransferredEventArgs { NativeData = lockedPtr, ImageInfo = imgInfo });
+                    SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { NativeData = lockedPtr, ImageInfo = imgInfo });
                 }
                 else
                 {
-                    OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                    SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
                 }
             }
             catch (Exception ex)
             {
-                OnTransferError(new TransferErrorEventArgs { Exception = ex });
+                SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { Exception = ex });
             }
             finally
             {
@@ -921,11 +936,11 @@ namespace NTwain
                 {
                     imgInfo = null;
                 }
-                OnDataTransferred(new DataTransferredEventArgs { FileDataPath = filePath, ImageInfo = imgInfo });
+                SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { FileDataPath = filePath, ImageInfo = imgInfo });
             }
             else
             {
-                OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
             }
         }
 
@@ -995,7 +1010,7 @@ namespace NTwain
                             //}
                             if (DGImage.ImageInfo.Get(out imgInfo) == ReturnCode.Success)
                             {
-                                OnDataTransferred(new DataTransferredEventArgs { MemData = xferredData.ToArray(), ImageInfo = imgInfo });
+                                SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { MemData = xferredData.ToArray(), ImageInfo = imgInfo });
                             }
                             else
                             {
@@ -1004,13 +1019,13 @@ namespace NTwain
                         }
                         else
                         {
-                            OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                            SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
                         }
                     }
                 }
                 catch (Exception ex)
                 {
-                    OnTransferError(new TransferErrorEventArgs { Exception = ex });
+                    SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { Exception = ex });
                 }
                 finally
                 {
@@ -1130,12 +1145,12 @@ namespace NTwain
                     }
                     else
                     {
-                        OnTransferError(new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
+                        SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { ReturnCode = xrc, SourceStatus = this.GetSourceStatus() });
                     }
                 }
                 catch (Exception ex)
                 {
-                    OnTransferError(new TransferErrorEventArgs { Exception = ex });
+                    SafeSyncableRaiseOnEvent(OnTransferError, TransferError, new TransferErrorEventArgs { Exception = ex });
                 }
                 finally
                 {
@@ -1157,7 +1172,7 @@ namespace NTwain
                     {
                         imgInfo = null;
                     }
-                    OnDataTransferred(new DataTransferredEventArgs { FileDataPath = finalFile, ImageInfo = imgInfo });
+                    SafeSyncableRaiseOnEvent(OnDataTransferred, DataTransferred, new DataTransferredEventArgs { FileDataPath = finalFile, ImageInfo = imgInfo });
                 }
             }
         }

README.markdown

@@ -20,9 +20,15 @@ and how it works in general. Except for certain "important" calls that drive the
 TWAIN state change, most triplet operations are only availble as-is so you will need to know
 when and how to use them. There are no high-level, single-line scan-a-page-for-me-now functions.
 
-At the moment this lib does not provide ways to parse transferred image data and require
-consumers to do the conversion. The winform project contains one such 
-example for handling DIB image in native transfer.
-
 The main class to use is TwainSession. New it up, hook into the events, and start calling
-all the TWAIN functions provided through it.
+all the TWAIN functions provided through it.
+
+Caveats
+--------------------------------------
+At the moment this lib does not provide ways to parse transferred image data and require
+consumers to do the conversion themselves. The winform project contains one such 
+example for handling DIB image in native transfer using the CommonWin32 lib.
+
+Because it hosts its own message thread, the event callbacks will likely be from another thread. 
+If you would like things marshalled to a "UI" thread then set the SynchronizationContext property
+to the one from the UI thread. This part is highly experimental.

Tests/Tester.WPF/TwainVM.cs

@@ -11,6 +11,7 @@ using System.Windows.Media.Imaging;
 using CommonWin32;
 using System.Threading;
 using GalaSoft.MvvmLight.Messaging;
+using System.Diagnostics;
 
 namespace Tester.WPF
 {
@@ -22,7 +23,7 @@ namespace Tester.WPF
         public TwainVM()
             : base(TWIdentity.CreateFromAssembly(DataGroups.Image | DataGroups.Audio, Assembly.GetEntryAssembly()))
         {
-
+            this.SynchronizationContext = SynchronizationContext.Current;
         }
 
         private ImageSource _image;
@@ -63,7 +64,6 @@ namespace Tester.WPF
                     Button = System.Windows.MessageBoxButton.OK
                 });
             }
-            base.OnTransferError(e);
         }
 
         protected override void OnTransferReady(TransferReadyEventArgs e)
@@ -82,24 +82,22 @@ namespace Tester.WPF
                 };
                 var rc = this.DGControl.SetupFileXfer.Set(fileSetup);
             }
-            base.OnTransferReady(e);
         }
 
         protected override void OnDataTransferred(DataTransferredEventArgs e)
         {
-            App.Current.Dispatcher.Invoke(new Action(() =>
+            //App.Current.Dispatcher.Invoke(new Action(() =>
+            //{
+            if (e.NativeData != IntPtr.Zero)
             {
-                if (e.NativeData != IntPtr.Zero)
+                Image = e.NativeData.GetWPFBitmap();
-                {
+            }
-                    Image = e.NativeData.GetWPFBitmap();
+            else if (!string.IsNullOrEmpty(e.FileDataPath))
-                }
+            {
-                else if (!string.IsNullOrEmpty(e.FileDataPath))
+                var img = new BitmapImage(new Uri(e.FileDataPath));
-                {
+                Image = img;
-                    var img = new BitmapImage(new Uri(e.FileDataPath));
+            }
-                    Image = img;
+            //}));
-                }
-            }));
-            base.OnDataTransferred(e);
         }
 
         public void TestCapture(IntPtr hwnd)

Tests/Tester.Winform/TestForm.cs

@@ -61,10 +61,21 @@ namespace Tester.Winform
         {
             var appId = TWIdentity.CreateFromAssembly(DataGroups.Image, Assembly.GetEntryAssembly());
             _twain = new TwainSession(appId);
+            // either set this and don't worry about threads during events,
+            // or don't and invoke during the events yourselv
+            _twain.SynchronizationContext = SynchronizationContext.Current;
+            _twain.StateChanged += (s, e) =>
+            {
+                Debug.WriteLine("State change on thread " + Thread.CurrentThread.ManagedThreadId);
+                //this.BeginInvoke(new Action(() =>
+                //{
+                //    Debug.WriteLine("State change marshaled to thread " + Thread.CurrentThread.ManagedThreadId);
+                //}));
+            };
             _twain.DataTransferred += (s, e) =>
             {
-                this.Invoke(new Action(() =>
+                //this.Invoke(new Action(() =>
-                {
+                //{
                     if (pictureBox1.Image != null)
                     {
                         pictureBox1.Image.Dispose();
@@ -72,7 +83,6 @@ namespace Tester.Winform
                     }
                     if (e.NativeData != IntPtr.Zero)
                     {
-                        //_ptrTest = e.Data;
                         var img = e.NativeData.GetDrawingBitmap();
                         if (img != null)
                             pictureBox1.Image = img;
@@ -82,17 +92,17 @@ namespace Tester.Winform
                         var img = new Bitmap(e.FileDataPath);
                         pictureBox1.Image = img;
                     }
-                }));
+                //}));
             };
             _twain.SourceDisabled += (s, e) =>
             {
-                this.Invoke(new Action(() =>
+                //this.Invoke(new Action(() =>
-                {
+                //{
                     btnStopScan.Enabled = false;
                     btnStartCapture.Enabled = true;
                     panelOptions.Enabled = true;
                     LoadSourceCaps();
-                }));
+                //}));
             };
             _twain.TransferReady += (s, e) =>
             {