Logging-Abstraktionen, Debug/Trace

using System;
using System.Diagnostics;

// Demo: show Debug/Trace after adding a ConsoleTraceListener
public class Program
{
  public static void Main(string[] args)
  {
    // By default, console apps may not show Debug/Trace. Add a listener.
    Trace.Listeners.Clear();
    Trace.Listeners.Add(new ConsoleTraceListener());

    Debug.WriteLine("Debug: only in debug builds (often)");
    Trace.WriteLine("Trace: in all builds (commonly)");

    Trace.TraceInformation("Info message");
    Trace.TraceWarning("Warning message");
    Trace.TraceError("Error message");
  }
}

using System;
using System.Diagnostics;

// Demo: TraceSource can group logs by name and level.
public class Program
{
  public static void Main(string[] args)
  {
    var src = new TraceSource("Calc", SourceLevels.Information);
    src.Listeners.Clear();
    src.Listeners.Add(new ConsoleTraceListener());

    src.TraceEvent(TraceEventType.Information, 1001, "Starting");
    src.TraceEvent(TraceEventType.Warning, 1002, "Low precision");
    src.TraceEvent(TraceEventType.Error, 1003, "Divide by zero prevented");
    src.Flush();
    src.Close();
  }
}

using System;

// Minimal ILogger-like abstraction for beginners.
public interface ILogger
{
  void Info(string msg);
  void Warn(string msg);
  void Error(string msg);
}

public class ConsoleLogger : ILogger
{
  private readonly string _name;
  public ConsoleLogger(string name) { _name = name; }

  public void Info(string msg)  { Console.WriteLine("[INFO] "  + _name + " - " + msg); }
  public void Warn(string msg)  { Console.WriteLine("[WARN] "  + _name + " - " + msg); }
  public void Error(string msg) { Console.WriteLine("[ERROR] " + _name + " - " + msg); }
}

public class Program
{
  public static void Main(string[] args)
  {
    ILogger log = new ConsoleLogger("Checkout");
    log.Info("Start");
    log.Warn("Slow network");
    log.Error("Payment failed");
  }
}

using System;

// Add a timestamp and tiny key=value context.
public interface ILogger
{
  void Info(string msg, string contextKey, string contextValue);
}

public class ConsoleLogger : ILogger
{
  private readonly string _name;
  public ConsoleLogger(string name) { _name = name; }

  public void Info(string msg, string key, string value)
  {
    string stamp = DateTime.UtcNow.ToString("u"); // 2009-06-15 13:45:30Z
    Console.WriteLine(stamp + " [INFO] " + _name + " " + key + "=" + value + " :: " + msg);
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    ILogger log = new ConsoleLogger("Search");
    log.Info("Query executed", "q", "apple");
    log.Info("Cache miss", "userId", "42");
  }
}