This class supplies static methods and properties to provide tracing ability. The calls to the Trace methods and properties are executed only if tracing is enabled. (See the introduction to this chapter for instructions on enabling tracing.)

The static properties allow you to adjust the settings that are used when you call the methods. You can specify that output be indented a certain amount with IndentLevel or increase or decrease the IndentLevel by one using Indent( ) and Unindent( ). You can also adjust the number of spaces each indent level adds using IndentSize. AutoFlush makes sure that after each use of a Trace method, the Listeners are flushed.

Write( ) and WriteLine( ) simply write to each TraceListener in the Listeners collection (by default, this collection includes an instance of DefaultTraceListener). WriteIf( ) and WriteLineIf( ) do the same, but only if the specified condition evaluates to true. Assert( ) emits an error message if a condition evaluates to false, and Fail( ) always emits an error message.

One possible point of confusion is that Listeners is read-only. This means that you may not point Listeners to a different collection. You can, however, add new TraceListener objects to the TraceListenerCollection with the TraceListenerCollection.Add( ) method.

You can use the application configuration file to configure this class. Under the <system.diagnostics> element, add a <trace> element. You can set attributes for this element that correspond to Trace properties, as in <trace autoflush="true" indentsize="4"/>.

public sealed class Trace {
// Public Static Properties
   public static bool AutoFlush{set; get; }
   public static int IndentLevel{set; get; }
   public static int IndentSize{set; get; }
   public static TraceListenerCollection Listeners{get; }
// Public Static Methods
   public static void Assert(bool condition);
   public static void Assert(bool condition, string message);
   public static void Assert(bool condition, string message, string detailMessage);
   public static void Close( );
   public static void Fail(string message);
   public static void Fail(string message, string detailMessage);
   public static void Flush( );
   public static void Indent( );
   public static void Unindent( );
   public static void Write(object value);
   public static void Write(object value, string category);
   public static void Write(string message);
   public static void Write(string message, string category);
   public static void WriteIf(bool condition, object value);
   public static void WriteIf(bool condition, object value, string category);
   public static void WriteIf(bool condition, string message);
   public static void WriteIf(bool condition, string message, string category);
   public static void WriteLine(object value);
   public static void WriteLine(object value, string category);
   public static void WriteLine(string message);
   public static void WriteLine(string message, string category);
   public static void WriteLineIf(bool condition, object value);
   public static void WriteLineIf(bool condition, object value, string category);
   public static void WriteLineIf(bool condition, string message);
   public static void WriteLineIf(bool condition, string message, string category);
}