第七步 添加监测（Tracing）  
1．我们经常需要监测应用程序在一个时间区的情况，日志应用程序块为我们提供了Tracing的功能。  
2．在解决方案管理器中选择Calc\Calculator.cs文件，选择View | Code菜单命令，在方法Calculate中添加如下代码。

public string Calculate(int digits){
StringBuilder pi = new StringBuilder("3", digits + 2);
string result = null;
try{
if (digits > 0){
// TODO: Add Tracing around the calculation
using (new Tracer(Category.Trace)){
pi.Append(".");
for (int i = 0; i < digits; i += 9){
CalculatingEventArgs args;
args = new CalculatingEventArgs(pi.ToString(), i + 1);
OnCalculating(args);
// Break out if cancelled
if (args.Cancel == true) break;
// Calculate next 9 digits
int nineDigits = NineDigitsOfPi.StartingAt(i + 1);
int digitCount = Math.Min(digits - i, 9);
string ds = string.Format("{0:D9}", nineDigits);
pi.Append(ds.Substring(0, digitCount));
}
}
}
result = pi.ToString();
// Tell the world I've finished!
OnCalculated(new CalculatedEventArgs(result));
}
catch (Exception ex)  {
// Tell the world I've crashed!
OnCalculatorException(new CalculatorExceptionEventArgs(ex));
}
return result;
}

3．在解决方案管理器中选择App.config，选择View | Open With…菜单命令，选择Enterprise Library Configuration并单击OK按钮。  
4．选择Logging Application Block节点，设置TracingEnabled属性为True。  

5．添加新的TraceListener，选中Logging Application Block | Trace Listeners节点，并选择Action | New | FlatFile TraceListener菜单命令。

6．设置Formatter属性为Text Formatter。

7．添加新的监测类别。选中Logging Application Block | Category Sources节点，并选择Action | New | Category菜单命令。

8．设置Name属性为Trace，SourceLevels属性为ActivityTracing。

这里的类别名Trace将会在代码中使用，设置ActivityTracing级别只会在日志项开始和结束的时候记录监测日志信息。
9．右击新的类别Trace，并选择New | Trace Listener Reference，设置ReferencedTraceListener属性为FlatFile TraceListener。

10．选择菜单File | Save All保存应用程序的配置，并关闭Enterprise Library Configuration工具。
11．选择Debug | Start Without Debugging菜单命令并运行应用程序，在NumericUpDown控件中输入精度并点击Calculate按钮。
12．现在可以在文件trace.log中看到监测日志信息。

----------------------------------------
Timestamp: 13/12/2005 6:08:01 AM
Message: Start Trace: Activity '8c07ce3b-235b-4a51-bdcc-83a5997c989e' 
in method 'Calculate' at 71661842482 ticks
Category: Trace
Priority: 5
EventId: 1
Severity: Start
Title:TracerEnter
Machine: TAGGERT
Application Domain: EnoughPI.exe
Process Id: 6016
Process Name: C:\Program Files\Microsoft Enterprise Library\labs\cs
\Logging\exercises\ex01\begin\EnoughPI\bin\Debug\EnoughPI.exe
Win32 Thread Id: 6092
Thread Name:
Extended Properties:
----------------------------------------
----------------------------------------
Timestamp: 13/12/2005 6:08:01 AM
Message: End Trace: Activity '8c07ce3b-235b-4a51-bdcc-83a5997c989e' in
 method 'Calculate' at 71662624219 ticks (elapsed time: 0.218 seconds)
Category: Trace
Priority: 5
EventId: 1
Severity: Stop
Title:TracerExit
Machine: TAGGERT
Application Domain: EnoughPI.exe
Process Id: 6016
Process Name: C:\Program Files\Microsoft Enterprise Library\labs\cs\Logging\
exercises\ex01\begin\EnoughPI\bin\Debug\EnoughPI.exe
Win32 Thread Id: 6092
Thread Name:
Extended Properties:
----------------------------------------

13．关闭应用程序和Visual Studio。  
完成后的解决方案代码如C:\Program Files\Microsoft Enterprise Library January 2006\labs\cs\Logging\exercises\ex01\end所示。