如何比較兩個資料夾的內容 (LINQ) (Visual Basic)
本例示範三種比較兩個檔案清單的方式︰
查詢指定兩個檔案清單是否完全相同的布林值。
查詢交集，以擷取這兩個資料夾都有的檔案。
查詢集合差異，以擷取一個資料夾中有而另一個沒有的檔案。
注意
這裡顯示的技巧可用於比較任何類型的物件序列。
這裡顯示的 FileComparer 類別會示範如何一起使用自訂比較子類別和標準查詢運算子。 此類別不適用於實際案例。 它僅使用每個檔案以位元組計的名稱和長度，來判斷每個資料夾的內容是否相同。 在實際案例中，您應該修改此比較子以執行更嚴格的相等檢查。
範例
Module CompareDirs
Public Sub Main()
' Create two identical or different temporary folders
' on a local drive and add files to them.
' Then set these file paths accordingly.
Dim pathA As String = "C:\TestDir"
Dim pathB As String = "C:\TestDir2"
' Take a snapshot of the file system.
Dim dir1 As New System.IO.DirectoryInfo(pathA)
Dim dir2 As New System.IO.DirectoryInfo(pathB)
Dim list1 = dir1.GetFiles("*.*", System.IO.SearchOption.AllDirectories)
Dim list2 = dir2.GetFiles("*.*", System.IO.SearchOption.AllDirectories)
' Create the FileCompare object we'll use in each query
Dim myFileCompare As New FileCompare
' This query determines whether the two folders contain
' identical file lists, based on the custom file comparer
' that is defined in the FileCompare class.
' The query executes immediately because it returns a bool.
Dim areIdentical As Boolean = list1.SequenceEqual(list2, myFileCompare)
If areIdentical = True Then
Console.WriteLine("The two folders are the same.")
Else
Console.WriteLine("The two folders are not the same.")
End If
' Find common files in both folders. It produces a sequence and doesn't execute
' until the foreach statement.
Dim queryCommonFiles = list1.Intersect(list2, myFileCompare)
If queryCommonFiles.Count() > 0 Then
Console.WriteLine("The following files are in both folders:")
For Each fi As System.IO.FileInfo In queryCommonFiles
Console.WriteLine(fi.FullName)
Next
Else
Console.WriteLine("There are no common files in the two folders.")
End If
' Find the set difference between the two folders.
' For this example we only check one way.
Dim queryDirAOnly = list1.Except(list2, myFileCompare)
Console.WriteLine("The following files are in dirA but not dirB:")
For Each fi As System.IO.FileInfo In queryDirAOnly
Console.WriteLine(fi.FullName)
Next
' Keep the console window open in debug mode
Console.WriteLine("Press any key to exit.")
Console.ReadKey()
End Sub
' This implementation defines a very simple comparison
' between two FileInfo objects. It only compares the name
' of the files being compared and their length in bytes.
Public Class FileCompare
Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo)
Public Function Equals1(ByVal x As System.IO.FileInfo, ByVal y As System.IO.FileInfo) _
As Boolean Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo).Equals
If (x.Name = y.Name) And (x.Length = y.Length) Then
Return True
Else
Return False
End If
End Function
' Return a hash that reflects the comparison criteria. According to the
' rules for IEqualityComparer(Of T), if Equals is true, then the hash codes must
' also be equal. Because equality as defined here is a simple value equality, not
' reference identity, it is possible that two or more objects will produce the same
' hash code.
Public Function GetHashCode1(ByVal fi As System.IO.FileInfo) _
As Integer Implements System.Collections.Generic.IEqualityComparer(Of System.IO.FileInfo).GetHashCode
Dim s As String = fi.Name & fi.Length
Return s.GetHashCode()
End Function
End Class
End Module
編譯程式碼
使用 System.Linq 命名空間的 Imports 陳述式建立 Visual Basic 主控台應用程式專案。
