如何：比较两个文件夹的内容 (LINQ)
此示例演示比较两个文件列表的三种方法：
查询一个指定两个文件列表是否相同的布尔值。
查询用于检索同时位于两个文件夹中的文件的交集。
查询用于检索位于一个文件夹中但不在另一个文件夹中的文件的差集。
.gif "说明")
说明可以修改上述这些方法以便对任意类型的对象序列进行比较。
此处显示的 FileComparer 类演示如何将自定义比较器类与标准查询运算符一起使用。该类不是为在实际方案中使用而设计的。它只是使用每个文件的名称和长度（以字节为单位）来确定每个文件夹的内容是否相同。在实际方案中，应对此比较器进行修改以执行更严格的相等性检查。
示例
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
namespace QueryCompareTwoDirs
{
class CompareDirs
{
static void Main(string[] args)
{
// Create two identical or different temporary folders
// on a local drive and change these file paths.
string pathA = @"C:\TestDir";
string pathB = @"C:\TestDir2";
System.IO.DirectoryInfo dir1 = new System.IO.DirectoryInfo(pathA);
System.IO.DirectoryInfo dir2 = new System.IO.DirectoryInfo(pathB);
// Take a snapshot of the file system.
IEnumerable<System.IO.FileInfo> list1 = dir1.GetFiles("*.*", System.IO.SearchOption.AllDirectories);
IEnumerable<System.IO.FileInfo> list2 = dir2.GetFiles("*.*", System.IO.SearchOption.AllDirectories);
//A custom file comparer defined below
FileCompare myFileCompare = 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.
bool areIdentical = list1.SequenceEqual(list2, myFileCompare);
if (areIdentical == true)
{
Console.WriteLine("the two folders are the same");
}
else
{
Console.WriteLine("The two folders are not the same");
}
// Find the common files. It produces a sequence and doesn't
// execute until the foreach statement.
var queryCommonFiles = list1.Intersect(list2, myFileCompare);
if (queryCommonFiles.Count() > 0)
{
Console.WriteLine("The following files are in both folders:");
foreach (var v in queryCommonFiles)
{
Console.WriteLine(v.FullName); //shows which items end up in result list
}
}
else
{
Console.WriteLine("There are no common files in the two folders.");
}
// Find the set difference between the two folders.
// For this example we only check one way.
var queryList1Only = (from file in list1
select file).Except(list2, myFileCompare);
Console.WriteLine("The following files are in list1 but not list2:");
foreach (var v in queryList1Only)
{
Console.WriteLine(v.FullName);
}
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
// 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.
class FileCompare : System.Collections.Generic.IEqualityComparer<System.IO.FileInfo>
{
public FileCompare() { }
public bool Equals(System.IO.FileInfo f1, System.IO.FileInfo f2)
{
return (f1.Name == f2.Name &&
f1.Length == f2.Length);
}
// Return a hash that reflects the comparison criteria. According to the
// rules for IEqualityComparer<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 int GetHashCode(System.IO.FileInfo fi)
{
string s = String.Format("{0}{1}", fi.Name, fi.Length);
return s.GetHashCode();
}
}
}
编译代码
创建面向 .NET Framework 3.5 版的 Visual Studio 项目。默认情况下，该项目具有对 System.Core.dll 的引用以及针对 System.Linq 命名空间的 using 指令 (C#) 或 Imports 语句 (Visual Basic)。在 C# 项目中，添加 System.IO 命名空间的 using 指令。
将代码复制到项目中。
按 F5 编译并运行程序。
按任意键退出控制台窗口。
可靠编程
若要对多种类型的文档和文件的内容执行大量查询操作，请考虑使用 Windows Desktop Search（Windows 桌面搜索）引擎。