Fixed creating/opening/closing twainsession multiple times in an app not working.

Tests/Tester.WPF/App.xaml

@@ -1,7 +1,7 @@
 <Application x:Class="Tester.WPF.App"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             StartupUri="MainWindow.xaml">
+             StartupUri="Dummy.xaml">
 	<Application.Resources>
         <ResourceDictionary>
             <!-- Dummy Style, anything you won't use goes -->

Tests/Tester.WPF/Dummy.xaml

@@ -0,0 +1,12 @@
+<Window x:Class="Tester.WPF.Dummy"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        Title="Dummy" Height="300" Width="300">
+    <Grid>
+        <StackPanel VerticalAlignment="Center">
+            <Button Content="Open scan window" Click="Button_Click" Margin="4 0"></Button>
+            <TextBlock Text="This is to test opening/closing multiple twain sessions in an app" Margin="8"
+                       TextWrapping="Wrap"></TextBlock>
+        </StackPanel>
+    </Grid>
+</Window>

Tests/Tester.WPF/Dummy.xaml.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Shapes;
+
+namespace Tester.WPF
+{
+    /// <summary>
+    /// Interaction logic for Dummy.xaml
+    /// </summary>
+    public partial class Dummy : Window
+    {
+        public Dummy()
+        {
+            InitializeComponent();
+        }
+
+        private void Button_Click(object sender, RoutedEventArgs e)
+        {
+            new MainWindow().ShowDialog();
+        }
+    }
+}

Tests/Tester.WPF/MainWindow.xaml.cs

@@ -4,6 +4,7 @@ using NTwain;
 using NTwain.Data;
 using System;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.Linq;
 using System.Windows;
 using System.Windows.Controls;
@@ -51,13 +52,18 @@ namespace Tester.WPF
                 });
             }
         }
-
+        protected override void OnClosing(CancelEventArgs e)
+        {
+            e.Cancel = _twainVM.State > 4;
+            base.OnClosing(e);
+        }
         protected override void OnClosed(EventArgs e)
         {
             if (_twainVM.State == 4)
             {
                 _twainVM.CurrentSource.Close();
             }
+            _twainVM.Close();
             base.OnClosed(e);
         }
 
@@ -68,6 +74,8 @@ namespace Tester.WPF
             // use this for internal msg loop
             //var rc = _twainVM.Open();
             // use this to hook into current app loop
+
+
             var rc = _twainVM.Open(new WpfMessageLoopHook(new WindowInteropHelper(this).Handle));
 
             if (rc == ReturnCode.Success)
@@ -82,6 +90,15 @@ namespace Tester.WPF
 
         private void SrcList_SelectionChanged(object sender, SelectionChangedEventArgs e)
         {
+
+            //var test = new NTwain.Internals.InternalMessageLoopHook();
+            //test.StartTest();
+            //test.BeginInvoke(() =>
+            //{
+            //    Debug.WriteLine("doodle");
+            //    test.StopTest();
+            //});
+
             if (_twainVM.State == 4)
             {
                 _twainVM.CurrentSource.Close();

Tests/Tester.WPF/Tester.WPF.csproj

@@ -80,7 +80,14 @@
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>
     </ApplicationDefinition>
+    <Compile Include="Dummy.xaml.cs">
+      <DependentUpon>Dummy.xaml</DependentUpon>
+    </Compile>
     <Compile Include="ViewModels\TwainVM.cs" />
+    <Page Include="Dummy.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="MainWindow.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>

Tests/Tester.WPF/ViewModels/TwainVM.cs

@@ -3,6 +3,7 @@ using GalaSoft.MvvmLight.Messaging;
 using NTwain;
 using NTwain.Data;
 using System;
+using System.IO;
 using System.Reflection;
 using System.Threading;
 using System.Windows.Media;
@@ -76,12 +77,23 @@ namespace Tester.WPF
                 var fileSetup = new TWSetupFileXfer
                 {
                     Format = wantFormat,
-                    FileName = System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "test.tif")
+                    FileName = GetUniqueName(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "test", ".tif")
                 };
                 var rc = this.CurrentSource.DGControl.SetupFileXfer.Set(fileSetup);
             }
         }
 
+        private string GetUniqueName(string dir, string name, string ext)
+        {
+            var filePath = Path.Combine(dir, name + ext);
+            int next = 1;
+            while (File.Exists(filePath))
+            {
+                filePath = Path.Combine(dir, string.Format("{0} ({1}){2}", name, next++, ext));
+            }
+            return filePath;
+        }
+
         protected override void OnDataTransferred(DataTransferredEventArgs e)
         {
             ImageSource img = null;