Expanded source disabled event args.

src/NTwain/CustomEventArgs.cs

@@ -0,0 +1,34 @@
+using NTwain.Data;
+using System;
+
+namespace NTwain
+{
+    /// <summary>
+    /// Contains data for a TWAIN source event.
+    /// </summary>
+    public class DeviceEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Gets the detailed device event.
+        /// </summary>
+        public TW_DEVICEEVENT Data { get; internal set; }
+    }
+
+    /// <summary>
+    /// Contains data when data source came down from being enabled.
+    /// </summary>
+    public class SourceDisabledEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Gets the affected source.
+        /// </summary>
+        public DataSource Source { get; internal set; }
+
+        /// <summary>
+        /// Whether the source was enabled with UI-only (no transfer).
+        /// The app could do something different if this is <code>true</code>, such as
+        /// getting the <see cref="TW_CUSTOMDSDATA"/>.
+        /// </summary>
+        public bool UIOnly { get; internal set; }
+    }
+}

src/NTwain/Data/TwainTypesExtended.cs

@@ -980,14 +980,14 @@ namespace NTwain.Data
     /// <summary>
     /// Allows for a data source and application to pass custom data to each other.
     /// </summary>
-    partial struct TW_CUSTOMDSDATA
+    public partial struct TW_CUSTOMDSDATA
     {
         /// <summary>
         /// Length, in bytes, of data.
         /// </summary>
         public uint InfoLength { get { return _infoLength; } set { _infoLength = value; } }
         /// <summary>
-        /// Handle to memory containing InfoLength bytes of data.
+        /// Handle to memory containing <see cref="InfoLength"/> bytes of data.
         /// </summary>
         public IntPtr Data { get { return _hData; } set { _hData = value; } }
     }

src/NTwain/DeviceEventArgs.cs

@@ -1,17 +0,0 @@
-using NTwain.Data;
-using System;
-
-namespace NTwain
-{
-	/// <summary>
-	/// Contains data for a TWAIN source event.
-	/// </summary>
-	public class DeviceEventArgs : EventArgs
-	{
-		/// <summary>
-		/// Gets the detailed device event.
-		/// </summary>
-		/// <value>The device event.</value>
-		public TW_DEVICEEVENT Data { get; internal set; }
-	}
-}

src/NTwain/Triplets/Control/UserInterface.cs

@@ -10,7 +10,7 @@ namespace NTwain.Triplets.Control
     {
         internal UserInterface(TwainSession session) : base(session) { }
 
-        public ReturnCode DisableDS(ref TW_USERINTERFACE ui)
+        public ReturnCode DisableDS(ref TW_USERINTERFACE ui, bool wasUIonly)
         {
             var rc = ReturnCode.Failure;
 
@@ -42,7 +42,11 @@ namespace NTwain.Triplets.Control
             if (rc == ReturnCode.Success)
             {
                 Session.State = TwainState.S4;
-                Session.OnSourceDisabled(EventArgs.Empty);
+                Session.OnSourceDisabled(new SourceDisabledEventArgs
+                {
+                    Source = Session.CurrentSource,
+                    UIOnly = wasUIonly
+                });
             }
             return rc;
         }

src/NTwain/TwainSession.MsgHandling.cs

@@ -35,9 +35,10 @@ namespace NTwain
                     DoTransferRoutine();
                     break;
                 case Message.CloseDSReq:
-                    DGControl.UserInterface.DisableDS(ref _lastEnableUI);
+                    DGControl.UserInterface.DisableDS(ref _lastEnableUI, false);
                     break;
                 case Message.CloseDSOK:
+                    DGControl.UserInterface.DisableDS(ref _lastEnableUI, true);
                     break;
             }
         }

src/NTwain/TwainSession.Props.cs

@@ -50,13 +50,13 @@ namespace NTwain
         /// <summary>
         /// Occurs when an enabled source has been disabled (back to state 4).
         /// </summary>
-        public event EventHandler SourceDisabled;
+        public event EventHandler<SourceDisabledEventArgs> SourceDisabled;
 
         /// <summary>
         /// Raises the <see cref="SourceDisabled"/> event.
         /// </summary>
         /// <param name="e"></param>
-        internal protected virtual void OnSourceDisabled(EventArgs e)
+        internal protected virtual void OnSourceDisabled(SourceDisabledEventArgs e)
         {
             var handler = SourceDisabled;
             handler?.Invoke(this, e);