SD卡目录

Question

我想访问sd卡文件，并读取文件的所有内容。首先，我无法将sd卡的路径插入到我的计算机上，因为sd卡的名称可以更改。此外，我希望在我的目录路径中获得所有文件名。

目录中有太多的文件，它们的编号为"1.txt“、"2.txt”。但是我必须访问最后一个文件并读取最后一个文件行。我正在使用下面的代码。有什么建议吗？

public void readSDcard()
        {        
            //here i want to get names all files in the directory and select the last file
            string[] fileContents;          

            try
            {
                fileContents = File.ReadAllLines("F:\\MAX\\1.txt");// here i have to write any sd card directory path

                foreach (string line in fileContents)
                {
                    Console.WriteLine(line);
                }
            }
            catch (FileNotFoundException ex)
            {
                throw ex;
            }
        }

Answer 1

.NET框架没有提供一种方法来识别哪个驱动程序是SD卡(我怀疑根本没有可靠的方法来做到这一点，至少没有非常低级别的progaming，例如查询系统驱动程序)。您可以做的最好是检查DriveType属性的DriveInfo是否等于DriveType.Removable，但这也将选择所有闪存驱动器等。

但即便如此，您也需要一些其他信息来选择合适的SD卡(例如，计算机中可能有多个SD卡)。如果SD卡的卷标签将始终相同，您可以使用它来选择正确的驱动器。否则，您将不得不询问用户，他希望使用哪个可移动驱动器，如下图所示。

问题没有具体说明，last file是什么意思。它是最后创建的文件，最后修改的文件，最后被操作系统枚举的文件，还是文件名中最大的文件？所以我想你想要一个数量最多的文件。

public void readSDcard()
{
    var removableDives = System.IO.DriveInfo.GetDrives()
        //Take only removable drives into consideration as a SD card candidates
        .Where(drive => drive.DriveType == DriveType.Removable)
        .Where(drive => drive.IsReady)
        //If volume label of SD card is always the same, you can identify
        //SD card by uncommenting following line
        //.Where(drive => drive.VolumeLabel == "MySdCardVolumeLabel")
        .ToList();

    if (removableDives.Count == 0)
        throw new Exception("No SD card found!");

    string sdCardRootDirectory;

    if(removableDives.Count == 1)
    {
        sdCardRootDirectory = removableDives[0].RootDirectory.FullName;
    }
    else
    {
        //Let the user select, which drive to use
        Console.Write($"Please select SD card drive letter ({String.Join(", ", removableDives.Select(drive => drive.Name[0]))}): ");
        var driveLetter = Console.ReadLine().Trim();
        sdCardRootDirectory = driveLetter + ":\\";
    }

    var path = Path.Combine(sdCardRootDirectory, "MAX");

    //Here you have all files in that directory
    var allFiles = Directory.EnumerateFiles(path);

    //Select last file (with the greatest number in the file name)
    var lastFile = allFiles
        //Sort files in the directory by number in their file name
        .OrderByDescending(filename =>
        {
            //Convert filename to number
            var fn = Path.GetFileNameWithoutExtension(filename);
            if (Int64.TryParse(fn, out var fileNumber))
                return fileNumber;
            else
                return -1;//Ignore files with non-numerical file name
        })
        .FirstOrDefault();

    if (lastFile == null)
        throw new Exception("No file found!");

    string[] fileContents = File.ReadAllLines(lastFile);

    foreach (string line in fileContents)
    {
        Console.WriteLine(line);
    }
}