Adding new WinForms sample application (#452)

samples/CSharpWinForms/MemoryLogger.cs

@@ -0,0 +1,43 @@
+using System.Text;
+using Microsoft.Extensions.Logging;
+
+namespace CSharpWinForms;
+
+public class LogUpdatedEventArgs : EventArgs
+{
+    public string? Text { get; set; }
+}
+
+public class MemoryLogger : ILogger
+{
+    public event EventHandler<LogUpdatedEventArgs>? LogUpdated;
+    private readonly StringBuilder _sb = new();
+
+    public IDisposable? BeginScope<TState>(TState state) where TState : notnull
+    {
+        return null;
+    }
+
+    public bool IsEnabled(LogLevel logLevel)
+    {
+        return true;
+    }
+
+    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
+    {
+        lock (_sb) {
+            var message = formatter(state, exception);
+            if (exception != null) message += "\n" + exception.ToString();
+            Console.WriteLine("log: " + message);
+            _sb.AppendLine(message);
+            LogUpdated?.Invoke(this, new LogUpdatedEventArgs { Text = _sb.ToString() });
+        }
+    }
+
+    public override string ToString()
+    {
+        lock (_sb) {
+            return _sb.ToString();
+        }
+    }
+}