我在VB.NET中写过这个，但我对C＃也很满意。我有一个我想在Windows文件系统上找到的文件列表。根据文件名，我需要查看不同的目录。我拥有的文件列表是我在程序开头编译的列表（可以工作），它存储在未排序的DataTable中。这是我的方法。
DataTable文件列表（这可能每天都有所不同，有时甚至在1,000s以上）
- a_111.txt
- a_222.txt
- b_333.txt
- a_444.txt
- c_555.txt
- b_666.txt
根据文件名进行调查的目录
C:\a\ -- for files begin with a (variable name is A_folder)
C:\b\ -- for files begin with b (variable name is B_folder)
C:\c\ -- for files begin with c (variable name is C_folder)
代码：
If DataTableofFiles IsNot Nothing AndAlso DataTableofFiles.Rows.Count > 0 Then
For Each row as DataRow In DataTableofFiles.Rows
If row("FILENAME").ToString.StartsWith("a") Then
Dim a_WriteResultstoA as String = "a.csv"
functionfindfiles(A_folder, row("FILENAME").ToString, a_WriteResultstoA)
ElseIf row("FILENAME").ToString.StartsWith("b") Then
Dim b_WriteResultstoB as String = "b.csv"
functionfindfiles(B_folder, row("FILENAME").ToString, b_WriteResultstoB)
ElseIf row("FILENAME").ToString.StartsWith("C") Then
Dim c_WriteResultstoC as String = "c.csv"
functionfindfiles(C_folder, row("FILENAME").ToString, c_WriteResultstoC)
End If
Next
End If
Private Sub functionfindfiles(sourcefolder As String, filename as String, writetofile As String)
Try
For Each f As String In Directory.EnumerateFiles(sourcefolder, "*.*", SearchOption.AllDirectories) '<-- file enumeration
If Path.GetFileName(f).Equals(filename, StringComparison.OrdinalIgnoreCase) Then
Using fs As New FileStream(writetofile, FileMode.Append, FileAccess.Write, FileShare.Write)
Using sw As StreamWriter = New StreamWriter(fs)
If Not New FileInfo(writetofile).Length > 0 Then
For i As Integer = 0 To DataTableofFiles.Columns.Count - 1 Step 1
sw.Write(DataTableofFiles.Columns(i).ToString)
If i < DataTableofFiles.Columns.Count - 1 Then
sw.Write(",")
End If
Next
sw.WriteLine()
End If
For Each row As DataRow In DataTableofFiles.Rows
If row("FILENAME").ToString = filename Then
For i As Integer = 0 To DataTableofFiles.Columns.Count - 1 Step 1
If Not Convert.IsDBNull(row(i)) Then
sw.Write(row(i).ToString.Replace(vbLf, "").Replace(",", ";"))
End If
If i < DataTableofFiles.Columns.Count - 1 Then
sw.Write(",")
End If
Next
sw.WriteLine()
End If
Next
End Using
End Using
Else
'write results that are not found here to a file
End If
Next
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End Sub
在这种情况下，文件系统上的Enumeration将发生6次。如果我在目录中有很多文件，执行可能需要很长时间。有没有更好的方法可以减少文件枚举量？或者代码中的其他区域可以进行改进，以减少执行所需的额外操作？任何意见是极大的赞赏。谢谢！
答案 0 :(得分：1)
您的示例中没有枚举6次，您要枚举文件夹A 3次，文件夹B 2次，文件夹C 1次。要减少这些额外的枚举，您可以预处理数据表以构建每个文件夹的文件名列表，然后修改您的方法以处理文件名列表而不是单个文件名。我不是用VB编写的，所以这里有一个用c＃代码掩盖的答案（抱歉，我的想法不适合评论，这是一个糟糕的答案，因为它没有编译）。
请注意，我对您的方法所做的只是添加foreach (var filename in listOfFileNames)并将签名更改为接受List<string> listOfFileNames而不是string filename，并且调用者现在构建列表并完成数据表在为每个文件夹调用一次方法之前完全foreach。
If DataTableofFiles IsNot Nothing AndAlso DataTableofFiles.Rows.Count > 0 Then
List<string> allAFileNames = new List<string>();
List<string> allBFileNames = new List<string>();
List<string> allCFileNames = new List<string>();
For Each row as DataRow In DataTableofFiles.Rows
If row("FILENAME").ToString.StartsWith("a") Then
Dim a_WriteResultstoA as String = "a.csv"
allAFileNames.Add(row("FILENAME"));
ElseIf row("FILENAME").ToString.StartsWith("b") Then
Dim b_WriteResultstoB as String = "b.csv"
allBFileNames.Add(row("FILENAME"));
ElseIf row("FILENAME").ToString.StartsWith("C") Then
Dim c_WriteResultstoC as String = "c.csv"
allCFileNames.Add(row("FILENAME"));
End If
Next
if (allAFileNames.Count > 0)
{
functionfindfiles(A_folder, allAFileNames, a_WriteResultstoA);
}
if (allBFileNames.Count > 0)
{
functionfindfiles(B_folder, allBFileNames, b_WriteResultstoB)
}
if (allAFileNames.Count > 0)
{
functionfindfiles(C_folder, allCFileNames, c_WriteResultstoC)
}
End If
Private Sub functionfindfiles(sourcefolder As String, List<string> listOfFileNames, writetofile As String)
Try
For Each f As String In Directory.EnumerateFiles(sourcefolder, "*.*", SearchOption.AllDirectories) '<-- file enumeration
foreach (var filename in listOfFileNames)
{
If Path.GetFileName(f).Equals(filename, StringComparison.OrdinalIgnoreCase) Then
Using fs As New FileStream(writetofile, FileMode.Append, FileAccess.Write, FileShare.Write)
Using sw As StreamWriter = New StreamWriter(fs)
If Not New FileInfo(writetofile).Length > 0 Then
For i As Integer = 0 To DataTableofFiles.Columns.Count - 1 Step 1
sw.Write(DataTableofFiles.Columns(i).ToString)
If i < DataTableofFiles.Columns.Count - 1 Then
sw.Write(",")
End If
Next
sw.WriteLine()
End If
For Each row As DataRow In DataTableofFiles.Rows
If row("FILENAME").ToString = filename Then
For i As Integer = 0 To DataTableofFiles.Columns.Count - 1 Step 1
If Not Convert.IsDBNull(row(i)) Then
sw.Write(row(i).ToString.Replace(vbLf, "").Replace(",", ";"))
End If
If i < DataTableofFiles.Columns.Count - 1 Then
sw.Write(",")
End If
Next
sw.WriteLine()
End If
Next
End Using
End Using
Else
'write results that are not found here to a file
End If
}
Next
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End Sub