Author:水如烟
一、异常是避免不了的
异常是避免不了的。比如将一个八位数字字串转换为相应的日期。
初始的代码如下：
Public Class Dig8ToDateTime
Private Const DIG8_PATTERN As String = "\b(\d{4})(\d{2})(\d{2})\b"
Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}"
'将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25"
Private Shared Function ToDateFormat(ByVal Value As String) As String
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT)
End Function
Public Shared Function ToDateTime(ByVal Value As String) As DateTime
Return DateTime.Parse(ToDateFormat(Value))
End Function
End Class
当接受的字串真是符合日期转换时，当然一切正常。
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Console.WriteLine(Dig8ToDateTime.ToDateTime("20051031").ToLongDateString)
End Sub
'输出结果:2005年10月31日
但是当字串不符合日期转换时，就发生异常了。
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Console.WriteLine(Dig8ToDateTime.ToDateTime("2005093").ToLongDateString)
End Sub
在这个类,能够避免预知的错误吗？能够利用Try...Catch...Finnaly吗？无论我怎么努力，我发现，无法避免，也不能使用Try...Catch。我就算告诉用户，你的输入错了，但我也无法输出合理的结果。能Return Nothing吗？不能！Nothing在DataTime里头就是0001年1月1日。为此，我只能什么都不处理，就让它异常好了。
二、异常真的不能避免吗
老天，我象是自打嘴巴了。
为了正常使用Dig8ToDateTime，我必须在用户界面上来检测输入是否合法。当我做到了这一步时，认为合法了，我发现，结果已经出来了，根本没有再使用Dig8ToDateTime这个类的必要。就是说，Dig8ToDateTime类毫无使用价值。
可我喜欢这个类，它在合法输入时带给我方便。现在，我变通一下，在输出结果前强制自检，不经自检，就不能使用Dig8ToDateTime.ToDateTime。
现在的代码如下：
Public Class Dig8ToDateTime
Private Const DIG8_PATTERN As String = "\b(\d{4})(\d{2})(\d{2})\b"
Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}"
Private Shared IsOK As Boolean
Private Shared Result As DateTime
'将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25"
Private Shared Function ToDateFormat(ByVal Value As String) As String
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT)
End Function
Public Shared Function CheckInput(ByVal Value As String) As Boolean
Try
Result = DateTime.Parse(ToDateFormat(Value))
IsOK = True
Catch ex As Exception
IsOK = False
End Try
Return IsOK
End Function
Public Shared Function Value() As DateTime
If Not IsOK Then
Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _
"Dim t As DateTime" & System.Environment.NewLine & _
"If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _
" t = Dig8ToDateTime.Value" & System.Environment.NewLine & _
"Else " & System.Environment.NewLine & _
" MsgBox(""输入错误"") " & System.Environment.NewLine & _
"End If")
End If
IsOK = False
Return Result
End Function
End Class
用户(这里指编程者)在使用这个类，在不知其特殊用法的情况下，一般是这样写的：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dig8ToDateTime.CheckInput("20050930")
Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString)
End Sub
在合法输入时，是正确的；不合法时，当然会发生异常：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dig8ToDateTime.CheckInput("2005093")
Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If Dig8ToDateTime.CheckInput("200509") Then
Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString)
Else
MsgBox("输入错误")
End If
End Sub
三、尽早预防异常
如果事前知道输入非法，那就可以即时回头，告知用户。下面，我加强了对数字合理性的判别。
Public Class Dig8ToDateTime
Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b"
Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}"
Private Shared IsOK As Boolean
Private Shared Result As DateTime
'将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25"
Private Shared Function ToDateFormat(ByVal Value As String) As String
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT)
End Function
Public Shared Function CheckInput(ByVal Value As String) As Boolean
Dim f As String = ToDateFormat(Value)
If Not f.Length = 10 Then 'Return False
IsOK = False
Return IsOK
End If
Try
Result = DateTime.Parse(f)
IsOK = True
Catch ex As Exception
IsOK = False
End Try
Return IsOK
End Function
Public Shared Function Value() As DateTime
If Not IsOK Then
Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _
"Dim t As DateTime" & System.Environment.NewLine & _
"If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _
" t = Dig8ToDateTime.Value" & System.Environment.NewLine & _
"Else " & System.Environment.NewLine & _
" MsgBox(""输入错误"") " & System.Environment.NewLine & _
"End If")
End If
IsOK = False
Return Result
End Function
End Class
四、尽可能减少异常抛出时间
Dig8ToDateTime类内还是不能避开异常的发生。闰年的二月，每月的31，不好判断。是能判断，可要做到的话，那这个类真没价值了。我只好用Try...Catch来应付。真遇到这种的非法输入时，肯定会发生异常，只不过是将异常控制在Try块内。这里还有没有改进的地方？既然避免不了异常的抛出，能不能缩短抛出的时间？以下想法只是估测，实际不知有没有用。
当运行环境遇到异常时，NET会寻找异常的类型，在运行库的异常数组里找，找到匹配的了，才抛出这个异常。我想的是能不能缩短它寻找的时间。看了帮助文档，DateTime.Parse()抛出异常的类型是FormatException，我就用它来代替Exception。实际上有没有效果呢，我真不知道。
Public Class Dig8ToDateTime
Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b"
Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}"
Private Shared IsOK As Boolean
Private Shared Result As DateTime
'将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25"
Private Shared Function ToDateFormat(ByVal Value As String) As String
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT)
End Function
Public Shared Function CheckInput(ByVal Value As String) As Boolean
Dim f As String = ToDateFormat(Value)
If Not f.Length = 10 Then 'Return False
IsOK = False
Return IsOK
End If
Try
Result = DateTime.Parse(f)
IsOK = True
Catch ex As FormatException
IsOK = False
End Try
Return IsOK
End Function
Public Shared Function Value() As DateTime
If Not IsOK Then
Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _
"Dim t As DateTime" & System.Environment.NewLine & _
"If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _
" t = Dig8ToDateTime.Value" & System.Environment.NewLine & _
"Else " & System.Environment.NewLine & _
" MsgBox(""输入错误"") " & System.Environment.NewLine & _
"End If")
End If
IsOK = False
Return Result
End Function
End Class
这个类，我现在只能做成这样了。最后发现，无论如何，异常还是免不了的。并且，我还主动的生成新的异常New ApplicationException。
最后是这样，将Value改成属性。
''' -----------------------------------------------------------------------------
''' Project : LzmTW.Common
''' Class : Common.Dig8ToDateTime
'''
''' -----------------------------------------------------------------------------
''' <summary>
''' 将8位数字串转换为日期
''' </summary>
''' <remarks>
''' 请按 "IF CheckInput(Value) Then 
Else EndIf" 方式使用
''' </remarks>
''' <history>
''' [lzmtw] 2005-10-26 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Class Dig8ToDateTime
'日期型数字匹配正则表达式
Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b"
Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}"
Private Shared _IsOK As Boolean
Private Shared _Result As DateTime
Private Sub New()
End Sub
Private Shared Function ToDateFormat(ByVal Value As String) As String '将20051210转换为2005-12-10
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT)
End Function
''' -----------------------------------------------------------------------------
''' <summary>
''' 输入
''' </summary>
''' <param name="Value">8位数字串</param>
''' <returns></returns>
''' <remarks>
''' </remarks>
''' <history>
''' [lzmtw] 2005-10-26 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Shared Function CheckInput(ByVal Value As String) As Boolean
Dim f As String = ToDateFormat(Value)
If Not f.Length = 10 Then
_IsOK = False
Return _IsOK
End If
Try
_Result = DateTime.Parse(f)
_IsOK = True
Catch ex As FormatException
_IsOK = False
End Try
Return _IsOK
End Function
''' -----------------------------------------------------------------------------
''' <summary>
''' 返回值
''' </summary>
''' <value></value>
''' <remarks>
''' 按 "IF CheckInput(Value) Then Else EndIf" 方式使用
''' </remarks>
''' <history>
''' [lzmtw] 2005-10-26 Created
''' </history>
''' -----------------------------------------------------------------------------
Public Shared ReadOnly Property Value() As DateTime
Get
If Not _IsOK Then
Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _
"Dim t As DateTime" & System.Environment.NewLine & _
"If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _
" t = Dig8ToDateTime.Value" & System.Environment.NewLine & _
"Else " & System.Environment.NewLine & _
" MsgBox(""输入错误"") " & System.Environment.NewLine & _
"End If")
End If
_IsOK = False
Return _Result
End Get
End Property
End Class
测试代码：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim Dig8Converter As LzmTW.Common.Dig8ToDateTime
With Dig8Converter
If .CheckInput(Me.TextBox1.Text) Then
Me.TextBox2.Text = .Value.ToLongDateString
Else
Me.TextBox2.Text = "输入错误"
'如显示异常信息 Console.WriteLine(.Value)
End If
End With
End Sub
一、异常是避免不了的
异常是避免不了的。比如将一个八位数字字串转换为相应的日期。
初始的代码如下：
Public Class Dig8ToDateTime
Private Const DIG8_PATTERN As String = "\b(\d{4})(\d{2})(\d{2})\b" Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}" '将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25" Private Shared Function ToDateFormat(ByVal Value As String) As String
Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT) End Function Public Shared Function ToDateTime(ByVal Value As String) As DateTime Return DateTime.Parse(ToDateFormat(Value)) End FunctionEnd Class当接受的字串真是符合日期转换时，当然一切正常。
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Console.WriteLine(Dig8ToDateTime.ToDateTime("20051031").ToLongDateString) End Sub '输出结果:2005年10月31日但是当字串不符合日期转换时，就发生异常了。
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Console.WriteLine(Dig8ToDateTime.ToDateTime("2005093").ToLongDateString) End Sub在这个类,能够避免预知的错误吗？能够利用Try...Catch...Finnaly吗？无论我怎么努力，我发现，无法避免，也不能使用Try...Catch。我就算告诉用户，你的输入错了，但我也无法输出合理的结果。能Return Nothing吗？不能！Nothing在DataTime里头就是0001年1月1日。为此，我只能什么都不处理，就让它异常好了。
二、异常真的不能避免吗
老天，我象是自打嘴巴了。
为了正常使用Dig8ToDateTime，我必须在用户界面上来检测输入是否合法。当我做到了这一步时，认为合法了，我发现，结果已经出来了，根本没有再使用Dig8ToDateTime这个类的必要。就是说，Dig8ToDateTime类毫无使用价值。
可我喜欢这个类，它在合法输入时带给我方便。现在，我变通一下，在输出结果前强制自检，不经自检，就不能使用Dig8ToDateTime.ToDateTime。
现在的代码如下：
Public Class Dig8ToDateTime Private Const DIG8_PATTERN As String = "\b(\d{4})(\d{2})(\d{2})\b" Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}" Private Shared IsOK As Boolean Private Shared Result As DateTime '将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25" Private Shared Function ToDateFormat(ByVal Value As String) As String Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT) End Function Public Shared Function CheckInput(ByVal Value As String) As Boolean Try Result = DateTime.Parse(ToDateFormat(Value)) IsOK = True Catch ex As Exception IsOK = False End Try Return IsOK End Function Public Shared Function Value() As DateTime If Not IsOK Then Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _ "Dim t As DateTime" & System.Environment.NewLine & _ "If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _ " t = Dig8ToDateTime.Value" & System.Environment.NewLine & _ "Else " & System.Environment.NewLine & _ " MsgBox(""输入错误"") " & System.Environment.NewLine & _ "End If") End If IsOK = False Return Result End FunctionEnd Class用户(这里指编程者)在使用这个类，在不知其特殊用法的情况下，一般是这样写的：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dig8ToDateTime.CheckInput("20050930") Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString) End Sub在合法输入时，是正确的；不合法时，当然会发生异常：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dig8ToDateTime.CheckInput("2005093") Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString) End Sub
于是会修改代码：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click If Dig8ToDateTime.CheckInput("200509") Then Console.WriteLine(Dig8ToDateTime.Value.ToLongDateString) Else MsgBox("输入错误") End If End Sub三、尽早预防异常
如果事前知道输入非法，那就可以即时回头，告知用户。下面，我加强了对数字合理性的判别。
Public Class Dig8ToDateTime Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b" Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}" Private Shared IsOK As Boolean Private Shared Result As DateTime '将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25" Private Shared Function ToDateFormat(ByVal Value As String) As String Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT) End Function Public Shared Function CheckInput(ByVal Value As String) As Boolean Dim f As String = ToDateFormat(Value) If Not f.Length = 10 Then 'Return False IsOK = False Return IsOK End If Try Result = DateTime.Parse(f) IsOK = True Catch ex As Exception IsOK = False End Try Return IsOK End Function Public Shared Function Value() As DateTime If Not IsOK Then Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _ "Dim t As DateTime" & System.Environment.NewLine & _ "If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _ " t = Dig8ToDateTime.Value" & System.Environment.NewLine & _ "Else " & System.Environment.NewLine & _ " MsgBox(""输入错误"") " & System.Environment.NewLine & _ "End If") End If IsOK = False Return Result End FunctionEnd Class四、尽可能减少异常抛出时间
Dig8ToDateTime类内还是不能避开异常的发生。闰年的二月，每月的31，不好判断。是能判断，可要做到的话，那这个类真没价值了。我只好用Try...Catch来应付。真遇到这种的非法输入时，肯定会发生异常，只不过是将异常控制在Try块内。这里还有没有改进的地方？既然避免不了异常的抛出，能不能缩短抛出的时间？以下想法只是估测，实际不知有没有用。
当运行环境遇到异常时，NET会寻找异常的类型，在运行库的异常数组里找，找到匹配的了，才抛出这个异常。我想的是能不能缩短它寻找的时间。看了帮助文档，DateTime.Parse()抛出异常的类型是FormatException，我就用它来代替Exception。实际上有没有效果呢，我真不知道。
Public Class Dig8ToDateTime Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b" Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}" Private Shared IsOK As Boolean Private Shared Result As DateTime '将8位数字转换为日期表示格式，如"20051025"转换为"2005-10-25" Private Shared Function ToDateFormat(ByVal Value As String) As String Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT) End Function Public Shared Function CheckInput(ByVal Value As String) As Boolean Dim f As String = ToDateFormat(Value) If Not f.Length = 10 Then 'Return False IsOK = False Return IsOK End If Try Result = DateTime.Parse(f) IsOK = True Catch ex As FormatException IsOK = False End Try Return IsOK End Function Public Shared Function Value() As DateTime If Not IsOK Then Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _ "Dim t As DateTime" & System.Environment.NewLine & _ "If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _ " t = Dig8ToDateTime.Value" & System.Environment.NewLine & _ "Else " & System.Environment.NewLine & _ " MsgBox(""输入错误"") " & System.Environment.NewLine & _ "End If") End If IsOK = False Return Result End FunctionEnd Class这个类，我现在只能做成这样了。最后发现，无论如何，异常还是免不了的。并且，我还主动的生成新的异常New ApplicationException。
最后是这样，将Value改成属性。
''' -----------------------------------------------------------------------------''' Project : LzmTW.Common''' Class : Common.Dig8ToDateTime''' ''' -----------------------------------------------------------------------------''' <summary>''' 将8位数字串转换为日期''' </summary>''' <remarks>''' 请按 "IF CheckInput(Value) Then Else EndIf" 方式使用''' </remarks>''' <history>''' [lzmtw] 2005-10-26 Created''' </history>''' -----------------------------------------------------------------------------Public Class Dig8ToDateTime '日期型数字匹配正则表达式 Private Const DIG8_PATTERN As String = "\b(0\d{2}[1-9]|[1-9]\d{3})(0[1-9]|1[0-2])(0[1-9]|[1|2]\d|3[0-1])\b" Private Const DIG8_REPLACEMENT As String = "${1}-${2}-${3}" Private Shared _IsOK As Boolean Private Shared _Result As DateTime Private Sub New() End Sub Private Shared Function ToDateFormat(ByVal Value As String) As String '将20051210转换为2005-12-10 Return System.Text.RegularExpressions.Regex.Replace(Value, DIG8_PATTERN, DIG8_REPLACEMENT) End Function ''' ----------------------------------------------------------------------------- ''' <summary> ''' 输入 ''' </summary> ''' <param name="Value">8位数字串</param> ''' <returns></returns> ''' <remarks> ''' </remarks> ''' <history> ''' [lzmtw] 2005-10-26 Created ''' </history> ''' ----------------------------------------------------------------------------- Public Shared Function CheckInput(ByVal Value As String) As Boolean Dim f As String = ToDateFormat(Value) If Not f.Length = 10 Then _IsOK = False Return _IsOK End If Try _Result = DateTime.Parse(f) _IsOK = True Catch ex As FormatException _IsOK = False End Try Return _IsOK End Function ''' ----------------------------------------------------------------------------- ''' <summary> ''' 返回值 ''' </summary> ''' <value></value> ''' <remarks> ''' 按 "IF CheckInput(Value) Then Else EndIf" 方式使用 ''' </remarks> ''' <history> ''' [lzmtw] 2005-10-26 Created ''' </history> ''' ----------------------------------------------------------------------------- Public Shared ReadOnly Property Value() As DateTime Get If Not _IsOK Then Throw New ApplicationException("请使用如下方法" & System.Environment.NewLine & _ "Dim t As DateTime" & System.Environment.NewLine & _ "If Dig8ToDateTime.CheckInput(""20051201"") Then " & System.Environment.NewLine & _ " t = Dig8ToDateTime.Value" & System.Environment.NewLine & _ "Else " & System.Environment.NewLine & _ " MsgBox(""输入错误"") " & System.Environment.NewLine & _ "End If") End If _IsOK = False Return _Result End Get End PropertyEnd Class测试代码：
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim Dig8Converter As LzmTW.Common.Dig8ToDateTime With Dig8Converter If .CheckInput(Me.TextBox1.Text) Then Me.TextBox2.Text = .Value.ToLongDateString Else Me.TextBox2.Text = "输入错误" '如显示异常信息 Console.WriteLine(.Value) End If End With End Sub