SEBWIN-312: Implemented basic handling of whitelisted applications.

SafeExamBrowser.Applications.Contracts/IApplicationInstance.cs

@@ -30,19 +30,29 @@ namespace SafeExamBrowser.Applications.Contracts
 		/// </summary>
 		event IconChangedEventHandler IconChanged;
 
-		/// <summary>
-		/// Event fired when the application instance has been terminated.
-		/// </summary>
-		event InstanceTerminatedEventHandler Terminated;
-
 		/// <summary>
 		/// Event fired when the name or (document) title of the application instance has changed.
 		/// </summary>
 		event NameChangedEventHandler NameChanged;
 
+		/// <summary>
+		/// Event fired when the application instance has been terminated.
+		/// </summary>
+		event InstanceTerminatedEventHandler Terminated;
+
 		/// <summary>
 		/// Makes this instance the currently active one and brings it to the foreground.
 		/// </summary>
 		void Activate();
+
+		/// <summary>
+		/// Initializes the application instance.
+		/// </summary>
+		void Initialize();
+
+		/// <summary>
+		/// Terminates the application instance.
+		/// </summary>
+		void Terminate();
 	}
 }

SafeExamBrowser.Applications/ApplicationFactory.cs

@@ -14,16 +14,19 @@ using SafeExamBrowser.Applications.Contracts;
 using SafeExamBrowser.Core.Contracts;
 using SafeExamBrowser.Logging.Contracts;
 using SafeExamBrowser.Settings.Applications;
+using SafeExamBrowser.WindowsApi.Contracts;
 
 namespace SafeExamBrowser.Applications
 {
 	public class ApplicationFactory : IApplicationFactory
 	{
-		private ILogger logger;
+		private IModuleLogger logger;
+		private IProcessFactory processFactory;
 
-		public ApplicationFactory(ILogger logger)
+		public ApplicationFactory(IModuleLogger logger, IProcessFactory processFactory)
 		{
 			this.logger = logger;
+			this.processFactory = processFactory;
 		}
 
 		public FactoryResult TryCreate(WhitelistApplication settings, out IApplication application)
@@ -62,7 +65,7 @@ namespace SafeExamBrowser.Applications
 		{
 			var icon = new IconResource { Type = IconResourceType.Embedded, Uri = new Uri(executablePath) };
 			var info = new ApplicationInfo { IconResource = icon, Name = settings.DisplayName, Tooltip = settings.Description ?? settings.DisplayName };
-			var application = new ExternalApplication(executablePath, info);
+			var application = new ExternalApplication(executablePath, info, logger.CloneFor(settings.DisplayName), processFactory);
 
 			return application;
 		}

SafeExamBrowser.Applications/ApplicationInstanceIdentifier.cs

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using SafeExamBrowser.Applications.Contracts;
+
+namespace SafeExamBrowser.Applications
+{
+	internal class ApplicationInstanceIdentifier : InstanceIdentifier
+	{
+		internal int ProcessId { get; private set; }
+
+		public ApplicationInstanceIdentifier(int processId)
+		{
+			ProcessId = processId;
+		}
+
+		public override bool Equals(object other)
+		{
+			if (other is ApplicationInstanceIdentifier id)
+			{
+				return ProcessId == id.ProcessId;
+			}
+
+			return false;
+		}
+
+		public override int GetHashCode()
+		{
+			return ProcessId.GetHashCode();
+		}
+
+		public override string ToString()
+		{
+			return $"({ProcessId})";
+		}
+	}
+}

SafeExamBrowser.Applications/ExternalApplication.cs

@@ -6,38 +6,64 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+using System.Collections.Generic;
+using System.Linq;
 using SafeExamBrowser.Applications.Contracts;
 using SafeExamBrowser.Applications.Contracts.Events;
+using SafeExamBrowser.Logging.Contracts;
+using SafeExamBrowser.WindowsApi.Contracts;
 
 namespace SafeExamBrowser.Applications
 {
 	internal class ExternalApplication : IApplication
 	{
 		private string executablePath;
+		private IModuleLogger logger;
+		private IList<IApplicationInstance> instances;
+		private IProcessFactory processFactory;
 
 		public ApplicationInfo Info { get; }
 
 		public event InstanceStartedEventHandler InstanceStarted;
 
-		internal ExternalApplication(string executablePath, ApplicationInfo info)
+		internal ExternalApplication(string executablePath, ApplicationInfo info, IModuleLogger logger, IProcessFactory processFactory)
 		{
 			this.executablePath = executablePath;
 			this.Info = info;
+			this.logger = logger;
+			this.instances = new List<IApplicationInstance>();
+			this.processFactory = processFactory;
 		}
 
 		public void Initialize()
 		{
-			
+			// Nothing to do here for now.
 		}
 
 		public void Start()
 		{
-			
+			logger.Info("Starting application...");
+
+			var process = processFactory.StartNew(executablePath);
+			var id = new ApplicationInstanceIdentifier(process.Id);
+			var instance = new ExternalApplicationInstance(id, logger.CloneFor($"{Info.Name} {id}"), process);
+
+			instance.Initialize();
+			instances.Add(instance);
+			InstanceStarted?.Invoke(instance);
 		}
 
 		public void Terminate()
 		{
-			
+			if (instances.Any())
+			{
+				logger.Info("Terminating application...");
+			}
+
+			foreach (var instance in instances)
+			{
+				instance.Terminate();
+			}
 		}
 	}
 }

SafeExamBrowser.Applications/ExternalApplicationInstance.cs

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System;
+using System.Timers;
+using SafeExamBrowser.Applications.Contracts;
+using SafeExamBrowser.Applications.Contracts.Events;
+using SafeExamBrowser.Logging.Contracts;
+using SafeExamBrowser.WindowsApi.Contracts;
+
+namespace SafeExamBrowser.Applications
+{
+	internal class ExternalApplicationInstance : IApplicationInstance
+	{
+		private const int ONE_SECOND = 1000;
+
+		private ILogger logger;
+		private string name;
+		private IProcess process;
+		private Timer timer;
+
+		public InstanceIdentifier Id { get; }
+		public string Name { get; }
+
+		public event IconChangedEventHandler IconChanged { add { } remove { } }
+		public event NameChangedEventHandler NameChanged;
+		public event InstanceTerminatedEventHandler Terminated;
+
+		public ExternalApplicationInstance(InstanceIdentifier id, ILogger logger, IProcess process)
+		{
+			this.Id = id;
+			this.logger = logger;
+			this.process = process;
+		}
+
+		public void Activate()
+		{
+			var success = process.TryActivate();
+
+			if (!success)
+			{
+				logger.Warn("Failed to activate instance!");
+			}
+		}
+
+		public void Initialize()
+		{
+			process.Terminated += Process_Terminated;
+
+			timer = new Timer(ONE_SECOND);
+			timer.Elapsed += Timer_Elapsed;
+			timer.Start();
+
+			logger.Info("Initialized application instance.");
+		}
+
+		public void Terminate()
+		{
+			const int MAX_ATTEMPTS = 5;
+			const int TIMEOUT_MS = 500;
+
+			timer.Elapsed -= Timer_Elapsed;
+			timer?.Stop();
+
+			var terminated = process.HasTerminated;
+
+			for (var attempt = 0; attempt < MAX_ATTEMPTS && !terminated; attempt++)
+			{
+				terminated = process.TryClose(TIMEOUT_MS);
+			}
+
+			for (var attempt = 0; attempt < MAX_ATTEMPTS && !terminated; attempt++)
+			{
+				terminated = process.TryKill(TIMEOUT_MS);
+			}
+
+			if (terminated)
+			{
+				logger.Info("Successfully terminated application instance.");
+			}
+			else
+			{
+				logger.Warn("Failed to terminate application instance!");
+			}
+		}
+
+		private void Process_Terminated(int exitCode)
+		{
+			logger.Info($"Application instance has terminated with exit code {exitCode}.");
+			Terminated?.Invoke(Id);
+		}
+
+		private void Timer_Elapsed(object sender, ElapsedEventArgs e)
+		{
+			var success = process.TryGetWindowTitle(out var title);
+			var hasChanged = name?.Equals(title, StringComparison.Ordinal) != true;
+
+			// TODO: Use this and ensure log window doesn't hang on shutdown (if it is open)!
+			// logger.Warn($"Success: {success} HasChanged: {hasChanged}");
+
+			if (success && hasChanged)
+			{
+				name = title;
+				NameChanged?.Invoke(name);
+			}
+
+			timer.Start();
+		}
+	}
+}

SafeExamBrowser.Applications/SafeExamBrowser.Applications.csproj

@@ -55,7 +55,9 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ApplicationFactory.cs" />
+    <Compile Include="ApplicationInstanceIdentifier.cs" />
     <Compile Include="ExternalApplication.cs" />
+    <Compile Include="ExternalApplicationInstance.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>
@@ -75,6 +77,10 @@
       <Project>{30b2d907-5861-4f39-abad-c4abf1b3470e}</Project>
       <Name>SafeExamBrowser.Settings</Name>
     </ProjectReference>
+    <ProjectReference Include="..\SafeExamBrowser.WindowsApi.Contracts\SafeExamBrowser.WindowsApi.Contracts.csproj">
+      <Project>{7016f080-9aa5-41b2-a225-385ad877c171}</Project>
+      <Name>SafeExamBrowser.WindowsApi.Contracts</Name>
+    </ProjectReference>
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
 </Project>

SafeExamBrowser.Browser/BrowserApplicationInstance.cs

@@ -53,9 +53,9 @@ namespace SafeExamBrowser.Browser
 
 		public event DownloadRequestedEventHandler ConfigurationDownloadRequested;
 		public event IconChangedEventHandler IconChanged;
-		public event InstanceTerminatedEventHandler Terminated;
 		public event NameChangedEventHandler NameChanged;
 		public event PopupRequestedEventHandler PopupRequested;
+		public event InstanceTerminatedEventHandler Terminated;
 
 		public BrowserApplicationInstance(
 			AppConfig appConfig,
@@ -85,13 +85,13 @@ namespace SafeExamBrowser.Browser
 			window?.BringToForeground();
 		}
 
-		internal void Initialize()
+		public void Initialize()
 		{
 			InitializeControl();
 			InitializeWindow();
 		}
 
-		internal void Terminate()
+		public void Terminate()
 		{
 			window?.Close();
 		}

SafeExamBrowser.Browser/BrowserInstanceIdentifier.cs

@@ -12,7 +12,7 @@ namespace SafeExamBrowser.Browser
 {
 	internal class BrowserInstanceIdentifier : InstanceIdentifier
 	{
-		public int Value { get; private set; }
+		internal int Value { get; private set; }
 
 		public BrowserInstanceIdentifier(int id)
 		{

SafeExamBrowser.Client/CompositionRoot.cs

@@ -96,7 +96,8 @@ namespace SafeExamBrowser.Client
 			taskbar = BuildTaskbar();
 			terminationActivator = new TerminationActivator(ModuleLogger(nameof(TerminationActivator)));
 
-			var applicationFactory = new ApplicationFactory(ModuleLogger(nameof(ApplicationFactory)));
+			var processFactory = new ProcessFactory(ModuleLogger(nameof(ProcessFactory)));
+			var applicationFactory = new ApplicationFactory(ModuleLogger(nameof(ApplicationFactory)), processFactory);
 			var applicationMonitor = new ApplicationMonitor(TWO_SECONDS, ModuleLogger(nameof(ApplicationMonitor)), nativeMethods, new ProcessFactory(ModuleLogger(nameof(ProcessFactory))));
 			var displayMonitor = new DisplayMonitor(ModuleLogger(nameof(DisplayMonitor)), nativeMethods, systemInfo);
 			var explorerShell = new ExplorerShell(ModuleLogger(nameof(ExplorerShell)), nativeMethods);

SafeExamBrowser.UserInterface.Desktop/Controls/ActionCenterApplicationControl.xaml

@@ -21,7 +21,7 @@
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
         <TextBlock Grid.Row="0" x:Name="ApplicationName" Background="#99D3D3D3" FontWeight="Bold" Padding="5" TextAlignment="Center" />
-        <ContentControl Grid.Row="1" x:Name="ApplicationButton" />
+        <ContentControl Grid.Row="1" x:Name="ApplicationButton" FontWeight="Bold" />
         <StackPanel Grid.Row="2" x:Name="InstancePanel" Background="#99D3D3D3" Orientation="Vertical" />
     </Grid>
 </UserControl>

SafeExamBrowser.UserInterface.Desktop/Controls/TaskbarApplicationControl.xaml

@@ -23,6 +23,6 @@
                 </ScrollViewer>
             </Border>
         </Popup>
-        <Button x:Name="Button" Background="{StaticResource BackgroundBrush}" Click="Button_Click" Padding="4" Template="{StaticResource TaskbarButton}" Width="50" />
+        <Button x:Name="Button" Background="{StaticResource BackgroundBrush}" Padding="4" Template="{StaticResource TaskbarButton}" Width="50" />
     </Grid>
 </UserControl>

SafeExamBrowser.UserInterface.Mobile/Controls/ActionCenterApplicationControl.xaml

@@ -21,7 +21,7 @@
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
         <TextBlock Grid.Row="0" x:Name="ApplicationName" Background="#99D3D3D3" FontWeight="Bold" Padding="5" TextAlignment="Center" />
-        <ContentControl Grid.Row="1" x:Name="ApplicationButton" />
+        <ContentControl Grid.Row="1" x:Name="ApplicationButton" FontWeight="Bold" />
         <StackPanel Grid.Row="2" x:Name="InstancePanel" Background="#99D3D3D3" Orientation="Vertical" />
     </Grid>
 </UserControl>

SafeExamBrowser.UserInterface.Mobile/Controls/TaskbarApplicationControl.xaml

@@ -23,6 +23,6 @@
                 </ScrollViewer>
             </Border>
         </Popup>
-        <Button x:Name="Button" Background="{StaticResource BackgroundBrush}" Click="Button_Click" Padding="4" Template="{StaticResource TaskbarButton}" Width="60" />
+        <Button x:Name="Button" Background="{StaticResource BackgroundBrush}" Padding="4" Template="{StaticResource TaskbarButton}" Width="60" />
     </Grid>
 </UserControl>

SafeExamBrowser.WindowsApi.Contracts/IProcess.cs

@@ -40,6 +40,12 @@ namespace SafeExamBrowser.WindowsApi.Contracts
 		/// </summary>
 		event ProcessTerminatedEventHandler Terminated;
 
+		/// <summary>
+		/// Attempts to activate the process (i.e. bring its main window to the foreground). This may only work for interactive processes which have
+		/// a main window. Returns <c>true</c> if the process was successfully activated, otherwise <c>false</c>.
+		/// </summary>
+		bool TryActivate();
+
 		/// <summary>
 		/// Attempts to gracefully terminate the process by closing its main window. This will only work for interactive processes which have a main
 		/// window. Optionally waits the specified amount of time for the process to terminate. Returns <c>true</c> if the process has terminated,
@@ -47,6 +53,12 @@ namespace SafeExamBrowser.WindowsApi.Contracts
 		/// </summary>
 		bool TryClose(int timeout_ms = 0);
 
+		/// <summary>
+		/// Attempts to retrieve the title of the main window of the process. This will only work if for interactive processes which have a main
+		/// window. Returns <c>true</c> if the title was successfully retrieved, otherwise <c>false</c>.
+		/// </summary>
+		bool TryGetWindowTitle(out string title);
+
 		/// <summary>
 		/// Attempts to immediately kill the process. Optionally waits the specified amount of time for the process to terminate. Returns <c>true</c>
 		/// if the process has terminated, otherwise <c>false</c>.

SafeExamBrowser.WindowsApi/Kernel32.cs

@@ -19,7 +19,6 @@ namespace SafeExamBrowser.WindowsApi
 	internal class Kernel32
 	{
 		[DllImport("kernel32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool CloseHandle(IntPtr hObject);
 
 		[DllImport("kernel32.dll", SetLastError = true)]

SafeExamBrowser.WindowsApi/Process.cs

@@ -11,9 +11,12 @@ using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Management;
+using System.Runtime.InteropServices;
 using SafeExamBrowser.Logging.Contracts;
+using SafeExamBrowser.WindowsApi.Constants;
 using SafeExamBrowser.WindowsApi.Contracts;
 using SafeExamBrowser.WindowsApi.Contracts.Events;
+using SafeExamBrowser.WindowsApi.Types;
 
 namespace SafeExamBrowser.WindowsApi
 {
@@ -62,6 +65,31 @@ namespace SafeExamBrowser.WindowsApi
 			this.originalNameInitialized = true;
 		}
 
+		public bool TryActivate()
+		{
+			try
+			{
+				var success = User32.BringWindowToTop(process.MainWindowHandle);
+				var placement = new WINDOWPLACEMENT();
+
+				placement.length = Marshal.SizeOf(placement);
+				User32.GetWindowPlacement(process.MainWindowHandle, ref placement);
+
+				if (placement.showCmd == (int) ShowWindowCommand.ShowMinimized)
+				{
+					success &= User32.ShowWindow(process.MainWindowHandle, (int) ShowWindowCommand.Restore);
+				}
+
+				return success;
+			}
+			catch (Exception e)
+			{
+				logger.Error("Failed to activate process!", e);
+			}
+
+			return false;
+		}
+
 		public bool TryClose(int timeout_ms = 0)
 		{
 			try
@@ -90,6 +118,25 @@ namespace SafeExamBrowser.WindowsApi
 			return false;
 		}
 
+		public bool TryGetWindowTitle(out string title)
+		{
+			title = default(string);
+
+			try
+			{
+				process.Refresh();
+				title = process.MainWindowTitle;
+
+				return true;
+			}
+			catch (Exception e)
+			{
+				logger.Error("Failed to retrieve title of main window!", e);
+			}
+
+			return false;
+		}
+
 		public bool TryKill(int timeout_ms = 0)
 		{
 			try

SafeExamBrowser.WindowsApi/SafeExamBrowser.WindowsApi.csproj

@@ -51,6 +51,7 @@
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="Microsoft.CSharp" />
+    <Reference Include="System.Drawing" />
     <Reference Include="System.Management" />
   </ItemGroup>
   <ItemGroup>
@@ -91,6 +92,7 @@
     <Compile Include="Types\RECT.cs" />
     <Compile Include="Types\STARTUPINFO.cs" />
     <Compile Include="Types\Window.cs" />
+    <Compile Include="Types\WINDOWPLACEMENT.cs" />
     <Compile Include="User32.cs" />
   </ItemGroup>
   <ItemGroup>

SafeExamBrowser.WindowsApi/Types/WINDOWPLACEMENT.cs

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2019 ETH Zürich, Educational Development and Technology (LET)
+ * 
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+using System.Drawing;
+
+namespace SafeExamBrowser.WindowsApi.Types
+{
+	internal struct WINDOWPLACEMENT
+	{
+		public int length;
+		public int flags;
+		public int showCmd;
+		public Point ptMinPosition;
+		public Point ptMaxPosition;
+		public Rectangle rcNormalPosition;
+	}
+}

SafeExamBrowser.WindowsApi/User32.cs

@@ -24,7 +24,6 @@ namespace SafeExamBrowser.WindowsApi
 		internal static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool CloseClipboard();
 
 		[DllImport("user32.dll", SetLastError = true)]
@@ -34,15 +33,15 @@ namespace SafeExamBrowser.WindowsApi
 		internal static extern IntPtr CreateDesktop(string lpszDesktop, IntPtr lpszDevice, IntPtr pDevmode, int dwFlags, uint dwDesiredAccess, IntPtr lpsa);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
+		internal static extern bool BringWindowToTop(IntPtr hWnd);
+
+		[DllImport("user32.dll", SetLastError = true)]
 		internal static extern bool EmptyClipboard();
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool EnumDesktops(IntPtr hwinsta, EnumDesktopDelegate lpEnumFunc, IntPtr lParam);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool EnumWindows(EnumWindowsDelegate enumProc, IntPtr lParam);
 
 		[DllImport("user32.dll", SetLastError = true)]
@@ -60,6 +59,9 @@ namespace SafeExamBrowser.WindowsApi
 		[DllImport("user32.dll", SetLastError = true)]
 		internal static extern bool GetUserObjectInformation(IntPtr hObj, int nIndex, IntPtr pvInfo, int nLength, ref int lpnLengthNeeded);
 
+		[DllImport("user32.dll", SetLastError = true)]
+		internal static extern bool GetWindowPlacement(IntPtr hWnd, ref WINDOWPLACEMENT lpwndpl);
+
 		[DllImport("user32.dll", SetLastError = true)]
 		internal static extern int GetWindowText(IntPtr hWnd, StringBuilder strText, int maxCount);
 
@@ -70,15 +72,12 @@ namespace SafeExamBrowser.WindowsApi
 		internal static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool IsWindowVisible(IntPtr hWnd);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool OpenClipboard(IntPtr hWndNewOwner);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool PostMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);
 
 		[DllImport("user32.dll", SetLastError = true)]
@@ -91,25 +90,21 @@ namespace SafeExamBrowser.WindowsApi
 		internal static extern IntPtr SetWindowsHookEx(HookType hookType, HookDelegate lpfn, IntPtr hMod, uint dwThreadId);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
 
 		[DllImport("user32.dll", SetLastError = true)]
 		internal static extern bool SwitchDesktop(IntPtr hDesktop);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool SystemParametersInfo(SPI uiAction, uint uiParam, ref RECT pvParam, SPIF fWinIni);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool SystemParametersInfo(SPI uiAction, int uiParam, string pvParam, SPIF fWinIni);
 
 		[DllImport("user32.dll", SetLastError = true)]
 		internal static extern bool UnhookWinEvent(IntPtr hWinEventHook);
 
 		[DllImport("user32.dll", SetLastError = true)]
-		[return: MarshalAs(UnmanagedType.Bool)]
 		internal static extern bool UnhookWindowsHookEx(IntPtr hhk);
 	}
 }