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

sample/ConsoleDemo/Program.cs

@@ -14,9 +14,9 @@
 //
 #endregion
 
+using Serilog;
 using System;
 using System.Threading;
-using Serilog;
 
 namespace ConsoleDemo
 {
@@ -33,15 +33,23 @@ private static void Main(string[] args)
 
             try
             {
-                Console.WriteLine("Open a `notepad.exe` instance and press <enter> to continue...");
-                Console.ReadLine();
+                //Console.WriteLine("Open a `notepad.exe` instance and press <enter> to continue...");
+                //Console.ReadLine();
 
                 Console.WriteLine("Writing messages to the most recent Notepad you opened...");
 
                 Log.Debug("Getting started");
 
-                Log.Information("Hello {Name} from thread {ThreadId}", Environment.GetEnvironmentVariable("USERNAME"),
-                    Thread.CurrentThread.ManagedThreadId);
+                var startTime = DateTime.Now;
+
+                while (DateTime.Now - startTime < TimeSpan.FromMinutes(1))
+                {
+
+                    Log.Information("Hello {Name} from thread {ThreadId}", Environment.GetEnvironmentVariable("USERNAME"),
+                        Thread.CurrentThread.ManagedThreadId);
+
+                    Thread.Sleep(1000);
+                }
 
                 Log.Warning("No coins remain at position {@Position}", new { Lat = 25, Long = 134 });
 

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
 {
@@ -55,7 +57,10 @@ public override void Flush()
                     // No instances of Notepad found... Nothing to do
                     return;
                 }
+            }
 
+            if (_currentNotepadEditorHandle == IntPtr.Zero)
+            {
                 var notepadWindowHandle = currentNotepadProcess.MainWindowHandle;
 
                 var notepadEditorHandle = FindNotepadEditorHandle(notepadWindowHandle);
@@ -80,7 +85,16 @@ public override void Flush()
             // Write the log message to Notepad
             User32.SendMessage(_currentNotepadEditorHandle, User32.EM_REPLACESEL, (IntPtr)1, message);
 
-            buffer.Clear();
+            // Get how many characters are in the Notepad editor after putting in new text
+            var textLengthAfter = User32.SendMessage(_currentNotepadEditorHandle, User32.WM_GETTEXTLENGTH, IntPtr.Zero, IntPtr.Zero);
+
+            // If no change in textLength, reset editor handle to try to find it again.
+            if (textLengthAfter == textLength)
+                _currentNotepadEditorHandle = IntPtr.Zero;
+
+            // Otherwise, we clear the buffer
+            else
+                buffer.Clear();
         }
 
         protected override void Dispose(bool disposing)
@@ -120,6 +134,13 @@ private static IntPtr FindNotepadEditorHandle(IntPtr notepadWindowHandle)
                 return richEditHandle;
             }
 
+            // Issue #59 - Alternate way of finding the RichEditD2DPT class:
+            if (FindEditorHandleThroughChildWindows(notepadWindowHandle) is var richEditHandleFromChildren
+                && richEditHandleFromChildren != IntPtr.Zero)
+            {
+                return richEditHandleFromChildren;
+            }
+
             return User32.FindWindowEx(notepadWindowHandle, IntPtr.Zero, "Edit", null);
         }
 
@@ -130,5 +151,49 @@ private void EnsureNotDisposed()
                 throw new ObjectDisposedException(GetType().Name);
             }
         }
+
+        private static string GetClassNameFromWindow(IntPtr handle)
+        {
+            StringBuilder sb = new StringBuilder(256);
+            var ret = User32.GetClassName(handle, sb, sb.Capacity);
+            return ret != 0 ? sb.ToString() : string.Empty;
+        }
+
+        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>");
+            }
+
+            if (string.Equals(GetClassNameFromWindow(handle), "RichEditD2DPT", StringComparison.OrdinalIgnoreCase))
+            {
+                list.Add(handle);
+
+                // Stop enumerating - we found the one.
+                return false;
+            }
+
+            return true;
+        }
+
+        private static IntPtr FindEditorHandleThroughChildWindows(IntPtr notepadWindowHandle)
+        {
+            List<IntPtr> result = new List<IntPtr>(1);
+            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 +35,17 @@ 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);
+
+
+        // Needed for EnumChildWindows for registering a call back function.
+        public delegate bool Win32Callback(IntPtr hwnd, IntPtr lParam);
+
+        [DllImport("user32.Dll", CharSet = CharSet.Unicode, SetLastError = true)]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        public static extern bool EnumChildWindows(IntPtr parentHandle, Win32Callback callback, IntPtr lParam);
+
+        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+        public static extern int GetClassName(IntPtr hWnd, System.Text.StringBuilder lpClassName, int nMaxCount);
+
     }
 }