Changeset 2 for swappable message loop hook implementations.

NTwain/MessageLoopHooks.cs

@@ -0,0 +1,189 @@
+using NTwain.Internals;
+using System;
+using System.Threading;
+using System.Windows.Interop;
+
+namespace NTwain
+{
+    /// <summary>
+    /// An abstract class for TWAIN to hook into windows message loops.
+    /// </summary>
+    public abstract class MessageLoopHook
+    {
+        internal IntPtr Handle { get; set; }
+        internal SynchronizationContext SyncContext { get; set; }
+
+        internal abstract void Start(IWinMessageFilter filter);
+        internal abstract void Stop();
+
+        internal virtual void BeginInvoke(Action action)
+        {
+            if (SyncContext == null)
+            {
+                action();
+            }
+            else
+            {
+                SyncContext.Post(o =>
+                {
+                    action();
+                }, null);
+            }
+        }
+        internal virtual void Invoke(Action action)
+        {
+            if (SyncContext == null)
+            {
+                action();
+            }
+            else
+            {
+                SyncContext.Send(o =>
+                {
+                    action();
+                }, null);
+            }
+        }
+
+        internal void ThrowInvalidOp()
+        {
+            throw new InvalidOperationException(InvalidMessage);
+        }
+
+        internal virtual string InvalidMessage { get { return string.Empty; } }
+    }
+
+    /// <summary>
+    /// A <see cref="MessageLoopHook"/> for use in winform applications.
+    /// </summary>
+    public sealed class WindowsFormsMessageLoopHook : MessageLoopHook, System.Windows.Forms.IMessageFilter
+    {
+        IWinMessageFilter _filter;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WindowsFormsMessageLoopHook"/> class.
+        /// </summary>
+        /// <param name="hwnd">The handle to the app window.</param>
+        /// <exception cref="System.ArgumentException">A valid window handle is required.</exception>
+        public WindowsFormsMessageLoopHook(IntPtr hwnd)
+        {
+            if (hwnd == IntPtr.Zero) { throw new ArgumentException("A valid window handle is required."); }
+
+            if (!System.Windows.Forms.Application.MessageLoop)
+            {
+                ThrowInvalidOp();
+            }
+            var sync = SynchronizationContext.Current;
+            if (sync == null)
+            {
+                ThrowInvalidOp();
+            }
+            Handle = hwnd;
+            SyncContext = sync;
+        }
+        internal override string InvalidMessage
+        {
+            get
+            {
+                return "This can only be created on the Windows Forms UI thread.";
+            }
+        }
+
+        internal override void Start(IWinMessageFilter filter)
+        {
+            //Invoke(() =>
+            //{
+            _filter = filter;
+            System.Windows.Forms.Application.AddMessageFilter(this);
+            //});
+        }
+
+        internal override void Stop()
+        {
+            //Invoke(() =>
+            //{
+            System.Windows.Forms.Application.RemoveMessageFilter(this);
+            _filter = null;
+            //});
+        }
+
+
+        #region IMessageFilter Members
+
+        bool System.Windows.Forms.IMessageFilter.PreFilterMessage(ref System.Windows.Forms.Message m)
+        {
+            if (_filter != null)
+            {
+                return _filter.IsTwainMessage(m.HWnd, m.Msg, m.WParam, m.LParam);
+            }
+            return false;
+        }
+
+        #endregion
+    }
+
+    /// <summary>
+    /// A <see cref="MessageLoopHook"/> for use in WPF applications.
+    /// </summary>
+    public sealed class WpfMessageLoopHook : MessageLoopHook
+    {
+        HwndSource _hooker;
+        IWinMessageFilter _filter;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="WpfMessageLoopHook"/> class.
+        /// </summary>
+        /// <param name="hwnd">The handle to the app window.</param>
+        /// <exception cref="System.ArgumentException">A valid window handle is required.</exception>
+        public WpfMessageLoopHook(IntPtr hwnd)
+        {
+            if (hwnd == IntPtr.Zero) { throw new ArgumentException("A valid window handle is required."); }
+
+            if (System.Windows.Application.Current == null ||
+                !System.Windows.Application.Current.Dispatcher.CheckAccess())
+            {
+                ThrowInvalidOp();
+            }
+            var sync = SynchronizationContext.Current;
+            if (sync == null)
+            {
+                ThrowInvalidOp();
+            }
+            Handle = hwnd;
+            SyncContext = sync;
+        }
+        internal override string InvalidMessage
+        {
+            get
+            {
+                return "This can only be created on the WPF UI thread.";
+            }
+        }
+
+        internal override void Start(IWinMessageFilter filter)
+        {
+            _filter = filter;
+            _hooker = HwndSource.FromHwnd(Handle);
+            _hooker.AddHook(FilterMessage);
+        }
+
+        private IntPtr FilterMessage(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
+        {
+            if (_filter != null)
+            {
+                handled = _filter.IsTwainMessage(hwnd, msg, wParam, lParam);
+            }
+            return IntPtr.Zero;
+        }
+
+        internal override void Stop()
+        {
+            if (_hooker != null)
+            {
+                _hooker.RemoveHook(FilterMessage);
+                _hooker.Dispose();
+                _hooker = null;
+            }
+        }
+    }
+}