Procedura: confrontare il contenuto di due cartelle (LINQ)
Aggiornamento: novembre 2007
In questo esempio vengono illustrati tre modi per confrontare due elenchi di file:
Eseguendo una query per un valore booleano che specifica se i due elenchi di file sono identici.
Eseguendo una query per l'intersezione per recuperare i file presenti in entrambe le cartelle.
Eseguendo una query per la differenza degli insiemi per recuperare i file presenti in una cartella ma non nell'altra.
.gif "Nota")
Nota:Le tecniche illustrate in questo argomento possono essere adattate per confrontare sequenze di oggetti di qualsiasi tipo.
La classe FileComparer descritta in questo argomento illustra come utilizzare una classe di operatori di confronto personalizzata con gli operatori di query standard. La classe non è destinata all'utilizzo negli scenari reali. In questo caso vengono utilizzati solo il nome e la lunghezza in byte di ogni file per determinare se il contenuto di ogni cartella sia identico o meno. In uno scenario reale, è necessario modificare questo operatore di confronto per eseguire un controllo di uguaglianza più accurato.
Esempio
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 list1 = GetFiles(pathA)
Dim list2 = GetFiles(pathB)
' 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
' Function to retrieve a list of files. Note that this is a copy
' of the file information.
Function GetFiles(ByVal root As String) As IEnumerable(Of System.IO.FileInfo)
Return From file In My.Computer.FileSystem.GetFiles _
(root, FileIO.SearchOption.SearchAllSubDirectories, "*.*") _
Select New System.IO.FileInfo(file)
End Function
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";
// Take a snapshot of the file system.
IEnumerable<System.IO.FileInfo> list1 = GetFiles(pathA);
IEnumerable<System.IO.FileInfo> list2 = GetFiles(pathB);
//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 method assumes that the application has discovery
// permissions for all folders under the specified path.
static IEnumerable<System.IO.FileInfo> GetFiles(string path)
{
if (!System.IO.Directory.Exists(path))
throw new System.IO.DirectoryNotFoundException();
string[] fileNames = null;
List<System.IO.FileInfo> files = new List<System.IO.FileInfo>();
fileNames = System.IO.Directory.GetFiles(path, "*.*", System.IO.SearchOption.AllDirectories);
foreach (string name in fileNames)
{
files.Add(new System.IO.FileInfo(name));
}
return files;
}
}
// 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();
}
}
}
Compilazione del codice
Creare un progetto di Visual Studio destinato a .NET Framework versione 3.5. Per impostazione predefinita, il progetto contiene un riferimento a System.Core.dll e una direttiva using (C#) o un'istruzione Imports (Visual Basic) per lo spazio dei nomi System.Linq. Nei progetti C# aggiungere una direttiva using per lo spazio dei nomi System.IO.
Copiare il codice nel progetto.
Premere F5 per compilare ed eseguire il programma.
Premere un tasto per chiudere la finestra della console.
Programmazione efficiente
Per operazioni di query complesse sul contenuto di più tipi di documenti e file, utilizzare il motore Windows Desktop Search.