Added wrapping methods to userinterface triplets.

samples/NetCoreConsole/Program.cs

@@ -21,6 +21,7 @@ namespace ConsoleApp
                 using (var session = new TwainSession(config))
                 {
                     session.PropertyChanged += Session_PropertyChanged;
+                    session.SourceDisabled += Session_SourceDisabled;
 
                     if (session.Open(IntPtr.Zero) == NTwain.Data.ReturnCode.Success)
                     {
@@ -67,17 +68,24 @@ namespace ConsoleApp
             Console.ReadLine();
         }
 
-        private static void TestThisSource(TwainSession session, DataSource targetSrc)
+        private static void Session_SourceDisabled(object sender, EventArgs e)
         {
-            Console.WriteLine($"Testing data source {targetSrc}");
+            var session = (TwainSession)sender;
+            Console.WriteLine($"Session source disabled.");
+            session.CurrentSource.Close();
+        }
+
+        private static void TestThisSource(TwainSession session, DataSource source)
+        {
+            Console.WriteLine($"Testing data source {source}");
             Console.WriteLine();
 
-            targetSrc.Open();
+            source.Open();
 
             var testStatus = session.GetStatus();
             var testMessage = session.GetLocalizedStatus(ref testStatus);
 
-            targetSrc.Close();
+            var rc = source.ShowUI(IntPtr.Zero);
         }
 
         private static void Session_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)

src/NTwain/Data/TwainTypes.cs

@@ -532,9 +532,9 @@ namespace NTwain.Data
     [StructLayout(LayoutKind.Sequential, Pack = 2)]
     partial struct TW_USERINTERFACE
     {
-        TW_BOOL _showUI;
+        public TW_BOOL ShowUI;
-        TW_BOOL _modalUI;
+        public TW_BOOL ModalUI;
-        TW_HANDLE _hParent;
+        public TW_HANDLE hParent;
     }
 
     [StructLayout(LayoutKind.Sequential, Pack = 2)]

src/NTwain/Data/TwainTypesExtended.cs

@@ -2267,43 +2267,6 @@ namespace NTwain.Data
         public uint ReceiveSize { get => _ReceiveSize; }
     }
     
-    /// <summary>
-    /// This structure is used to handle the user interface coordination between an application and a
-    /// Source.
-    /// </summary>
-    partial struct TW_USERINTERFACE
-    {
-        /// <summary>
-        /// Set to TRUE by the application if the Source should activate its built-in user
-        /// interface. Otherwise, set to FALSE. Note that not all sources support ShowUI =
-        /// FALSE.
-        /// </summary>
-        public bool ShowUI
-        {
-            get { return _showUI > 0; }
-            set { _showUI = value ? TwainConst.True : TwainConst.False; }
-        }
-        /// <summary>
-        /// If ShowUI is TRUE, then an application setting this to TRUE requests the Source to
-        /// run Modal.
-        /// </summary>
-        public bool ModalUI
-        {
-            //get { return _modalUI > 0; } 
-            set { _modalUI = value ? TwainConst.True : TwainConst.False; }
-        }
-        /// <summary>
-        /// Microsoft Windows only: Application’s window handle. The Source designates
-        /// the hWnd as its parent when creating the Source dialog.
-        /// </summary>
-        public IntPtr Parent
-        {
-            //get { return _hParent; } 
-            set { _hParent = value; }
-        }
-    }
-
-
     /// <summary>
     /// Provides entry points required by TWAIN 2.0 Applications and Sources.
     /// </summary>

src/NTwain/DataSource.cs

@@ -34,6 +34,50 @@ namespace NTwain
         /// <returns></returns>
         public ReturnCode Close() => Session.DGControl.Identity.CloseDS(Identity32);
 
+        /// <summary>
+        /// Showing driver configuration UI if supported.
+        /// </summary>
+        /// <param name="windowHandle">The parent window handle if on Windows. Use <see cref="IntPtr.Zero"/> if not applicable.</param>
+        /// <param name="modal">if set to <c>true</c> the driver UI may be displayed as modal.</param>
+        /// <returns></returns>
+        public ReturnCode ShowUI(IntPtr windowHandle, bool modal = false)
+        {
+            var ui = new TW_USERINTERFACE
+            {
+                ShowUI = 1,
+                ModalUI = (ushort)(modal ? 1 : 0),
+                hParent = windowHandle
+            };
+            var rc = Session.DGControl.UserInterface.EnableDSUIOnly(ref ui);
+            if (rc == ReturnCode.Success)
+            {
+                Session._lastEnableUI = ui;
+            }
+            return rc;
+        }
+
+        /// <summary>
+        /// Enables the source for transferring data.
+        /// </summary>
+        /// <param name="showUI">if set to <c>true</c> then show driver UI. Not all sources support turning UI off.</param>
+        /// <param name="windowHandle">The parent window handle if on Windows. Use <see cref="IntPtr.Zero"/> if not applicable.</param>
+        /// <param name="modal">if set to <c>true</c> any driver UI may be displayed as modal.</param>
+        /// <returns></returns>
+        public ReturnCode Enable(bool showUI, IntPtr windowHandle, bool modal = false)
+        {
+            var ui = new TW_USERINTERFACE
+            {
+                ShowUI = (ushort)(showUI ? 1 : 0),
+                ModalUI = (ushort)(modal ? 1 : 0),
+                hParent = windowHandle
+            };
+            var rc = Session.DGControl.UserInterface.EnableDS(ref ui);
+            if (rc == ReturnCode.Success)
+            {
+                Session._lastEnableUI = ui;
+            }
+            return rc;
+        }
 
         /// <summary>
         /// Gets the source status. Useful after getting a non-success return code.

src/NTwain/Triplets/Control/UserInterface.cs

@@ -42,6 +42,7 @@ namespace NTwain.Triplets.Control
             if (rc == ReturnCode.Success)
             {
                 Session.State = TwainState.S4;
+                Session.OnSourceDisabled(EventArgs.Empty);
             }
             return rc;
         }
@@ -79,7 +80,7 @@ namespace NTwain.Triplets.Control
                 }
 
                 if (!(rc == ReturnCode.Success &&
-                    (!ui.ShowUI && rc == ReturnCode.CheckStatus)))
+                    (ui.ShowUI == 0 && rc == ReturnCode.CheckStatus)))
                 {
                     Session.State = TwainState.S4;
                 }

src/NTwain/TwainSession.MsgHandling.cs

@@ -13,6 +13,8 @@ namespace NTwain
 {
     partial class TwainSession
     {
+        internal TW_USERINTERFACE _lastEnableUI;
+
         private void HandleSourceMsg(Message msg)
         {
             switch (msg)
@@ -26,12 +28,23 @@ namespace NTwain
                     }
                     break;
                 case Message.XferReady:
+                    if (State < TwainState.S6)
+                    {
+                        State = TwainState.S6;
+                    }
+                    DoTransferRoutine();
                     break;
                 case Message.CloseDSReq:
+                    DGControl.UserInterface.DisableDS(ref _lastEnableUI);
                     break;
                 case Message.CloseDSOK:
                     break;
             }
         }
+
+        private void DoTransferRoutine()
+        {
+            throw new NotImplementedException();
+        }
     }
 }

src/NTwain/TwainSession.Props.cs

@@ -47,6 +47,20 @@ namespace NTwain
         ///// </summary>
         //public DGCustom DGCustom { get; set; }
 
+        /// <summary>
+        /// Occurs when an enabled source has been disabled (back to state 4).
+        /// </summary>
+        public event EventHandler SourceDisabled;
+
+        /// <summary>
+        /// Raises the <see cref="SourceDisabled"/> event.
+        /// </summary>
+        /// <param name="e"></param>
+        internal protected virtual void OnSourceDisabled(EventArgs e)
+        {
+            var handler = SourceDisabled;
+            handler?.Invoke(this, e);
+        }
 
         /// <summary>
         /// Occurs when the source has generated an event.