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70-562 Listeners


Listeners

System.Diagnostics.Trace is collectted by TraceListeners. A TraceListener is an object that receives trace outpout and writes it out. Writes to a file, asp.net, databse, external monitoring system.
When a trace listener is create it is added to the Trace.Listeners collection which lets the listener recieve all the output including asp.net.

All listeners are derived from the TraceListener abstract class which has a variety of methods. The tracelisteners are the same but differ by the type of media they are writting to.

The same data can go to mulitple listeners.

Fail: writes including the call stack
Write: Outputs the text
WRiteLine: Outputes with a craiage returen
Flush: Flushes the output buffer to the traget media
Close: Closes the uput stream in order to stop recieving the debugging and traing data.
DefaultTraceListener: ouputs to the output window, included in all the tracelisteners, others should be use to write elsewere
TextWriterTraceListener: Writes to a text file or a , nextowrk stream or console
EventLogTraceListener writes to a local or remote windows event log
ConsoleTraceListener: outputs to a console
DelimitedListeTraceListener: outputs to a stream
XmlWriterTraceListeners: To atext writer to a stream

They output in a different format to different listenres, can have mulitple listenrs.
Only messages written as Write or Warn are forwarded.

Both the Trace and Debug Classes share the same object, so writting to one is available to the other.

Trace switches: Lets you set the granularity of the messages sent to the listeners. They Derive from the System.Diagnostics.Switch class and are conto9led from the web,.config file. It this possible to configure the switch without recompling.

Various type of switches:
BooleanSwitch, toggles on or off. The instence is defined in code and should match the one in the web config, if it doesnt match, it is desabled.
TraceSwitch: if this switch is desiabled, it wont write, more granularity than boolean switch. Off, Error, Warning, Info, verbose, for example, warning includes Error.
SourceSwitch:

Switches are configured in the web.config, child of the configuration element, within the system.diagnositcs element, withing the switches element, the name can be any name defined but has to match thte one in the chosen in code.

The value is from 1 to 4 where 4 is verbose.

The default for depolyemnt is to have all switches to false.

After having created the switch, create the trace listeners in code to output tracing.

Trace listeners are int eh App_Code directory. They require the System.Diagnositics, and System.IIO namespaces.

Typicaly, listeners used are logfile and event log, create a switch, one boolean one multiswitch (TraceSwitch).

After having created the listener, it needs to be added to the collection of listeners, in Trace.Listeners.Add(EventListener).

Typically to get the path to a file iwthin the application, string appPath = HttpContext.Current.Request.PhysicalapolicationPath;

Different types of listeners require different types of preparation as seen in the case of getting the path to a log file example above.

Before writting, one makes a check to the boolean switch is enable, within that 'if' is the code that writes the trace listeners.

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