/// <devdoc>
///     This class is intended to use with the C# 'using' statement in
///     to activate an activation context for turning on visual theming at
///     the beginning of a scope, and have it automatically deactivated
///     when the scope is exited.
/// </devdoc>

[SuppressUnmanagedCodeSecurity]
internal class EnableThemingInScope : IDisposable
{
   // Private data
   private IntPtr cookie; // changed cookie from uint to IntPtr
   private static ACTCTX enableThemingActivationContext;
   private static IntPtr hActCtx;
   private static bool contextCreationSucceeded = false;

   public EnableThemingInScope(bool enable)
   {
     if (enable)
     {
       if (EnsureActivateContextCreated())
       {
         if (!ActivateActCtx(hActCtx, out cookie))
         {
           // Be sure cookie always zero if activation failed
           cookie = IntPtr.Zero;
         }
       }
     }
  }

  // Finalizer removed, that could cause Exceptions
  // ~EnableThemingInScope()
  // {
  //    Dispose(false);
  // }

  void IDisposable.Dispose()
  {
     Dispose(true);
     GC.SuppressFinalize(this);
  }

  private void Dispose(bool disposing)
  {
     if (cookie != IntPtr.Zero)
     {
        if (DeactivateActCtx(0, cookie))
        {
           // deactivation succeeded...
           cookie = IntPtr.Zero;
        }
     }
  }

  private bool EnsureActivateContextCreated()
  {
   lock (typeof(EnableThemingInScope))
   {
    if (!contextCreationSucceeded)
    {
     // Pull manifest from the .NET Framework install
     // directory

     string assemblyLoc = null;

     FileIOPermission fiop = new FileIOPermission(PermissionState.None);
     fiop.AllFiles = FileIOPermissionAccess.PathDiscovery;
     fiop.Assert();
     try
     {
        assemblyLoc = typeof(Object).Assembly.Location;
     }
     finally
     { 
        CodeAccessPermission.RevertAssert();
     }

     string manifestLoc = null;
     string installDir = null;
     if (assemblyLoc != null)
     {
        installDir = Path.GetDirectoryName(assemblyLoc);
        const string manifestName = "XPThemes.manifest";
        manifestLoc = Path.Combine(installDir, manifestName);
     }

     if (manifestLoc != null && installDir != null)
     {
         enableThemingActivationContext = new ACTCTX();
         enableThemingActivationContext.cbSize = Marshal.SizeOf(typeof(ACTCTX));
         enableThemingActivationContext.lpSource = manifestLoc;

         // Set the lpAssemblyDirectory to the install
         // directory to prevent Win32 Side by Side from
         // looking for comctl32 in the application
         // directory, which could cause a bogus dll to be
         // placed there and open a security hole.
         enableThemingActivationContext.lpAssemblyDirectory = installDir;
         enableThemingActivationContext.dwFlags = ACTCTX_FLAG_ASSEMBLY_DIRECTORY_VALID; 

         // Note this will fail gracefully if file specified
         // by manifestLoc doesn't exist.
         hActCtx = CreateActCtx(ref enableThemingActivationContext);
         contextCreationSucceeded = (hActCtx != new IntPtr(-1));
     }
    }

    // If we return false, we'll try again on the next call into
    // EnsureActivateContextCreated(), which is fine.
    return contextCreationSucceeded;
   }
  }

  // All the pinvoke goo...
  [DllImport("Kernel32.dll")]
  private extern static IntPtr CreateActCtx(ref ACTCTX actctx);

  // changed from uint to IntPtr according to 
  // https://www.pinvoke.net/default.aspx/kernel32.ActiveActCtx
  [DllImport("Kernel32.dll", SetLastError = true)]
  [return: MarshalAs(UnmanagedType.Bool)]
  private static extern bool ActivateActCtx(IntPtr hActCtx, out IntPtr lpCookie);

  // changed from uint to IntPtr according to 
  // https://www.pinvoke.net/default.aspx/kernel32.DeactivateActCtx
  [DllImport("Kernel32.dll", SetLastError = true)]
  [return: MarshalAs(UnmanagedType.Bool)]
  private static extern bool DeactivateActCtx(int dwFlags, IntPtr lpCookie);

  private const int ACTCTX_FLAG_ASSEMBLY_DIRECTORY_VALID = 0x004;

  private struct ACTCTX 
  {
     public int       cbSize;
     public uint      dwFlags;
     public string    lpSource;
     public ushort    wProcessorArchitecture;
     public ushort    wLangId;
     public string    lpAssemblyDirectory;
     public string    lpResourceName;
     public string    lpApplicationName;
  }
 }
}

using (new EnableThemingInScope(true))
{
    // The call all this mucking about is here for.
    VistaUnsafeNativeMethods.TaskDialogIndirect(ref config, out result, out radioButtonResult, out verificationFlagChecked);
 }