#眉標=.NET
#副標=.NET Namespace專欄
#大標= System.Diagnostics(上)程式監控和測試
#作者=文／彭靖灝

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Debug.WriteLine(“Hello, world!”)
Trace.WriteLine(“Hellp, world!”)
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程式1
Dim myTraceLog As _
New System.IO.FileStream("C:\Temp\myTraceLog.txt", _
   IO.FileMode.OpenOrCreate)
   ' Creates the new trace listener
myListener = New TextWriterTraceListener(myTraceLog)
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程式2
myListener.WriteLine(Now.ToLongTimeString & _
" : 開始呼叫授權作業")
If Authorize(txtCreditCardNo.Text, _
Decimal.Parse(txtAmount.Text)) Then
    strresult = "通過！"
Else
strResult = "拒絕！"
End If
lblResult.Text = strResult
myListener.WriteLine(Now.ToLongTimeString & _
" : 授權作業完成，結果：" & strResult)
myListener.Flush()
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程式3
Dim myFile As New _
FileStream("C:\Temp\ConsoleLog.txt", 
FileMode.OpenOrCreate)

Dim myTextListener As _
New TextWriterTraceListener(myFile)
Trace.Listeners.Add(myTextListener)

Dim myConsoleListener As _
New TextWriterTraceListener(System.Console.Out)
Trace.Listeners.Add(myConsoleListener)

Trace.WriteLine("追蹤結果輸出至所有Listener")

myConsoleListener.WriteLine
("追蹤結果只輸出到命令視窗。")
myTextListener.WriteLine
("追蹤結果只輸出到文字檔案。")

' 針對所有追蹤接聽器進行清空
Trace.Flush()
' 針對個別追蹤接聽器進行清空
myConsoleListener.Flush()
myTextListener.Flush()

' 以下程式碼相當於執行 myTextListener.Close
myTextListener.Close()
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程式4
Dim dbSwitch As New _
BooleanSwitch("DatabaseSwitch", "資料庫存取")
Dim apSwitch As New _
TraceSwitch("ApplicationSwitch", "應用程式作業")
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而在對應的.config檔中(Windows Form的程式是在app.config中指定，Web Form的程式是在web.config中指定)就會指定以下的標註：

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程式5
<system.diagnostics>
   <switches>
      <add name="DatabaseSwitch" value="1" />
      <add name="ApplicationSwitch" value="2" />
   </switches>
</system.diagnostics>
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程式6
Private Sub Form1_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
    Dim myTraceLog As New FileStream(_
"C:\Temp\myTraceLog.txt", FileMode.Append)
    ' Creates the new trace listener

    myListener = New TextWriterTraceListener(myTraceLog)
    myListener.WriteLine(Now.ToLongTimeString & _
" : 目前追蹤等級為 " & apSwitch.Level.ToString)
End Sub
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程式7 依據等級提供不同追蹤資訊

Private Sub btnAuthorize_Click(ByVal sender As _
System.Object, ByVal e As System.EventArgs) _
Handles btnAuthorize.Click
    Dim strResult As String
    If apSwitch.TraceInfo Then
        myListener.WriteLine(Now.ToLongTimeString & _
" : 開始呼叫授權作業")
    End If
    Trace
        If Authorize(txtCreditCardNo.Text, _
    Decimal.Parse(txtAmount.Text)) Then
            strResult = "通過！"
        Else
            strResult = "拒絕！"
        End If
    Catch ex As Exception
        If apSwitch.TraceError Then
          myListener.WriteLine(Now.ToLongTimeString & _
          " : 錯誤─" & ex.Message)
        End If
    End Try

    lblResult.Text = strResult
    If apSwitch.TraceInfo Then
    myListener.WriteLine(Now.ToLongTimeString & _
" : 授權作業完成，結果：" & strResult)
    End If
    myListener.Flush()
End Sub

Private Function Authorize(ByVal CreditCardNo As String, _
ByVal Amount As Decimal) As Boolean
    Dim bResult As Boolean
    If apSwitch.TraceVerbose Then
        myListener.WriteLine(Now.ToLongTimeString & _
" : 進行授權作業")
    End If
    If CreditCardNo.Substring(0, 1) = "0" And Amount > _
3000 Then
        bResult = False
    Else
        bResult = True
    End If
    If apSwitch.TraceVerbose Then
        myListener.WriteLine(Now.ToLongTimeString & _
" : 完成授權作業")
    End If
    Return bResult
End Function


Private Sub Form1_Closed(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Closed
    myListener.Close()
End Sub
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程式8
Private Sub Form1_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
    Dim myTraceLog As New FileStream("C:\Temp\myTraceLog.txt", _
       FileMode.Append)
    ' Creates the new trace listener

    myListener = New TextWriterTraceListener(myTraceLog)
    Trace.Listeners.Add(myListener)
    Trace.WriteLine(Now.ToLongDateString & "-" & _
        Now.ToLongTimeString & " : 程式啟動。")
    Trace.Indent()
    Trace.WriteLine(Now.ToLongTimeString & _
" : 目前追蹤等級為 " & apSwitch.Level.ToString)
End Sub

Private Sub Form1_Closed(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Closed
    Trace.Unindent()
    Trace.WriteLine(Now.ToLongTimeString & " : 程式結束")
    Trace.Close()
End Sub
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Trace.WriteLineIf(apSwitch.TraceError, _
Now.ToLongTimeString & " : 開始呼叫授權作業")
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在語法和作業方式上，它會顯得更簡潔，更直覺。
另外如果我們期望每次寫入追蹤訊息後，就直接傳送緩衝區的內容到接聽器中，除了自行控制叫用Flush方法之外，也可以指定Debug或Trace類別的AutoFlush屬性的值為True，讓追蹤器自行處理清除緩衝區的作業。
這些設定的作業除了透過程式控制之外，也可以透過設定檔來控制，下面的設定檔片段就指定縮排的空格數量為3個空白字元，同時關閉自動清除緩衝區的功能：

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程式9
<configuration>
<system.diagnostics>
<trace autoflush="false" indentsize="3" />
</system.diagnostics>
</configuration>
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