velopack/samples/CSharpWinForms/MemoryLogger.cs

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();
        }
    }
}