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HOW TO:查詢具有指定屬性或名稱的檔案

更新:2007 年 11 月

這個範例顯示如何尋找所指定目錄樹狀結構中具有所指定副檔名 (例如 ".txt") 的所有檔案。同時也會顯示如何根據建立時間傳回樹狀結構中最新或最舊的檔案。

範例

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;
    }
}

編譯程式碼

  • 建立一個以 .NET Framework 3.5 版為目標的 Visual Studio 專案。根據預設,專案有 System.Core.dll 的參考,以及 System.Linq 命名空間的 using 指示詞 (C#) 或 Imports 陳述式 (Visual Basic)。請在 C# 專案中,加入 System.IO 命名空間的 using 指示詞。

  • 將此程式碼複製至您的專案。

  • 按 F5 編譯和執行程式。

  • 按任何鍵離開主控台視窗。

穩固程式設計

如需對多種類型的文件和檔案內容執行大量查詢作業,可考慮使用 Windows 桌面搜尋引擎。

請參閱

概念

LINQ to Objects

LINQ 和檔案目錄