Implementing an alternate way of finding editor handle for new Notepad

* Adding needed interop definitions to enumerate child windows
* If first attempt using FindWindowEx with notepad process MainWindowHandle does not find editor handle, the search is done by enumerating child window handles for the notepad process MainWindowHandle.

Author: bstordrup

src/Serilog.Sinks.Notepad/Sinks/Notepad/Interop/NotepadTextWriter.cs

@@ -14,12 +14,14 @@
 //
 #endregion
 
+using Serilog.Debugging;
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
-using Serilog.Debugging;
 
 namespace Serilog.Sinks.Notepad.Interop
 {
@@ -120,6 +122,13 @@ private static IntPtr FindNotepadEditorHandle(IntPtr notepadWindowHandle)
                 return richEditHandle;
             }
 
+            // Issue #59 - Alternate way of finding the RichEditD2DPT class:
+            if (FindEditorHandleThroughChildWindows(notepadWindowHandle) is var childRichEditHandle
+                && childRichEditHandle != IntPtr.Zero)
+            {
+                return childRichEditHandle;
+            }
+
             return User32.FindWindowEx(notepadWindowHandle, IntPtr.Zero, "Edit", null);
         }
 
@@ -130,5 +139,40 @@ private void EnsureNotDisposed()
                 throw new ObjectDisposedException(GetType().Name);
             }
         }
+
+        private static bool EnumWindow(IntPtr handle, IntPtr pointer)
+        {
+            GCHandle gch = GCHandle.FromIntPtr(pointer);
+            List<IntPtr> list = gch.Target as List<IntPtr>;
+            if (list == null)
+            {
+                throw new InvalidCastException("GCHandle Target could not be cast as List<IntPtr>");
+            }
+
+            // We only want windows of class RichEditD2DPT.
+            if (User32.FindWindowEx(handle, IntPtr.Zero, "RichEditD2DPT", null) != IntPtr.Zero)
+            {
+                list.Add(handle);
+            }
+
+            return true;
+        }
+
+        private static IntPtr FindEditorHandleThroughChildWindows(IntPtr notepadWindowHandle)
+        {
+            List<IntPtr> result = new List<IntPtr>();
+            GCHandle listHandle = GCHandle.Alloc(result);
+            try
+            {
+                User32.Win32Callback childProc = new User32.Win32Callback(EnumWindow);
+                User32.EnumChildWindows(notepadWindowHandle, childProc, GCHandle.ToIntPtr(listHandle));
+            }
+            finally
+            {
+                if (listHandle.IsAllocated)
+                    listHandle.Free();
+            }
+            return result.FirstOrDefault();
+        }
     }
 }

src/Serilog.Sinks.Notepad/Sinks/Notepad/Interop/User32.cs

@@ -35,5 +35,16 @@ internal class User32
 
         [DllImport("User32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
         public static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);
+
+
+        [DllImport("user32.dll")]
+        public static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);
+
+        // Needed for EnumChildWindows for registering a call back function.
+        public delegate bool Win32Callback(IntPtr hwnd, IntPtr lParam);
+
+        [DllImport("user32.Dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        public static extern bool EnumChildWindows(IntPtr parentHandle, Win32Callback callback, IntPtr lParam);
     }
 }