如何：查询具有指定属性或名称的文件
更新：2007 年 11 月
此示例演示如何查找指定目录树中具有指定文件扩展名（例如“.txt”）的所有文件，还演示如何根据创建时间返回树中最新或最旧的文件。
示例
Module FindFileByExtension
Sub Main()
' Change the drive\path if necessary
Dim root As String = "C:\Program Files\Microsoft Visual Studio 9.0"
'Take a snapshot of the folder contents
Dim fileList = GetFiles(root)
' This query will produce the full path for all .txt files
' under the specified folder including subfolders.
' It orders the list according to the file name.
Dim fileQuery = From file In fileList _
Where file.Extension = ".txt" _
Order By file.Name _
Select file
For Each file In fileQuery
Console.WriteLine(file.FullName)
Next
' Create and execute a new query by using
' the previous query as a starting point.
' fileQuery is not executed again until the
' call to Last
Dim fileQuery2 = From file In fileQuery _
Order By file.CreationTime _
Select file.Name, file.CreationTime
' Execute the query
Dim newestFile = fileQuery2.Last
Console.WriteLine("\r\nThe newest .txt file is {0}. Creation time: {1}", _
newestFile.Name, newestFile.CreationTime)
' Keep the console window open in debug mode
Console.WriteLine("Press any key to exit.")
Console.ReadKey()
End Sub
' Function to retrieve a list of files. Note that this is a copy
' of the file information.
Function GetFiles(ByVal root As String) As System.Collections.Generic.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
class FindFileByExtension
{
// This query will produce the full path for all .txt files
// under the specified folder including subfolders.
// It orders the list according to the file name.
static void Main()
{
string startFolder = @"c:\program files\Microsoft Visual Studio 9.0\";
// Take a snapshot of the file system.
IEnumerable<System.IO.FileInfo> fileList = GetFiles(startFolder);
//Create the query
IEnumerable<System.IO.FileInfo> fileQuery =
from file in fileList
where file.Extension == ".txt"
orderby file.Name
select file;
//Execute the query. This might write out a lot of files!
foreach (System.IO.FileInfo fi in fileQuery)
{
Console.WriteLine(fi.FullName);
}
// Create and execute a new query by using the previous
// query as a starting point. fileQuery is not
// executed again until the call to Last()
var newestFile =
(from file in fileQuery
orderby file.CreationTime
select new { file.FullName, file.CreationTime })
.Last();
Console.WriteLine("\r\nThe newest .txt file is {0}. Creation time: {1}",
newestFile.FullName, newestFile.CreationTime);
// 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;
}
}
编译代码
创建一个面向 .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。
将此代码复制到您的项目。
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。