我一直在用这个:

public static void DelimitedAppend(this StringBuilder sb, string value, string delimiter)
{
    if (sb.Length > 0)
        sb.Append(delimiter);
    sb.Append(value);
}

这只是确保当字符串为空时不会插入分隔符。 例如，创建一个以逗号分隔的单词列表:

var farmAnimals = new[] { new { Species = "Dog", IsTasty = false }, new { Species = "Cat", IsTasty = false }, new { Species = "Chicken", IsTasty = true }, };
var soupIngredients = new StringBuilder();
foreach (var edible in farmAnimals.Where(farmAnimal => farmAnimal.IsTasty))
    soupIngredients.DelimitedAppend(edible.Species, ", ");

我们有一个部署工具可以在不同环境之间进行部署。由于文件可以标记为修改，但实际上没有不同，我想出了这个:

/// <summary>
/// Compares the files to see if they are different. 
/// First checks file size
/// Then modified if the file is larger than the specified size
/// Then compares the bytes
/// </summary>
/// <param name="file1">The source file</param>
/// <param name="file2">The destination file</param>
/// <param name="mb">Skip the smart check if the file is larger than this many megabytes. Default is 10.</param>
/// <returns></returns>
public static bool IsDifferentThan(this FileInfo file1, FileInfo file2, int mb = 10)
{
  var ret = false;

  // different size is a different file
  if(file1.Length != file2.Length) return true;

  // if the file times are different and the file is bigger than 10mb flag it for updating
  if(file1.LastWriteTimeUtc > file2.LastWriteTimeUtc && file1.Length > ((mb*1024)*1024)) return true;

  var f1 = File.ReadAllBytes(file1.FullName);
  var f2 = File.ReadAllBytes(file2.FullName);

  // loop through backwards because if they are different
  // it is more likely that the last few bytes will be different
  // than the first few
  for(var i = file1.Length - 1; i > 0; i--)
  {
    if(f1[i] != f2[i])
    {
      ret = true;
      break;
    }
  }

  return ret;
}

通过操作系统文件系统信息比较文件/目录。这对于比较共享和本地文件非常有用。

用法:

DirectoryInfo dir = new DirectoryInfo(@"C:\test\myShareDir");
Console.WriteLine(dir.IsSameFileAs(@"\\myMachineName\myShareDir"));

FileInfo file = new FileInfo(@"C:\test\myShareDir\file.txt");
Console.WriteLine(file.IsSameFileAs(@"\\myMachineName\myShareDir\file.txt"));

代码:

public static class FileExtensions
{
    struct BY_HANDLE_FILE_INFORMATION
    {
        public uint FileAttributes;
        public System.Runtime.InteropServices.ComTypes.FILETIME CreationTime;
        public System.Runtime.InteropServices.ComTypes.FILETIME LastAccessTime;
        public System.Runtime.InteropServices.ComTypes.FILETIME LastWriteTime;
        public uint VolumeSerialNumber;
        public uint FileSizeHigh;
        public uint FileSizeLow;
        public uint NumberOfLinks;
        public uint FileIndexHigh;
        public uint FileIndexLow;
    }

    //
    // CreateFile constants
    //
    const uint FILE_SHARE_READ = 0x00000001;
    const uint OPEN_EXISTING = 3;
    const uint GENERIC_READ = (0x80000000);
    const uint FILE_FLAG_BACKUP_SEMANTICS = 0x02000000;


    [DllImport("kernel32.dll", SetLastError = true)]
    static extern IntPtr CreateFile(
        string lpFileName,
        uint dwDesiredAccess,
        uint dwShareMode,
        IntPtr lpSecurityAttributes,
        uint dwCreationDisposition,
        uint dwFlagsAndAttributes,
        IntPtr hTemplateFile);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool GetFileInformationByHandle(IntPtr hFile, out BY_HANDLE_FILE_INFORMATION lpFileInformation);

    public static bool IsSameFileAs(this FileSystemInfo file, string path)
    {
        BY_HANDLE_FILE_INFORMATION fileInfo1, fileInfo2;
        IntPtr ptr1 = CreateFile(file.FullName, GENERIC_READ, FILE_SHARE_READ, IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, IntPtr.Zero);
        if ((int)ptr1 == -1)
        {
            System.ComponentModel.Win32Exception e = new System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error());
            throw e;
        }
        IntPtr ptr2 = CreateFile(path, GENERIC_READ, FILE_SHARE_READ, IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, IntPtr.Zero);
        if ((int)ptr2 == -1)
        {
            System.ComponentModel.Win32Exception e = new System.ComponentModel.Win32Exception(Marshal.GetLastWin32Error());
            throw e;
        }
        GetFileInformationByHandle(ptr1, out fileInfo1);
        GetFileInformationByHandle(ptr2, out fileInfo2);

        return ((fileInfo1.FileIndexHigh == fileInfo2.FileIndexHigh) &&
            (fileInfo1.FileIndexLow == fileInfo2.FileIndexLow));
    }
}

从集合中加载默认设置的一种更简单的方法(在现实生活中，我使用它来填充来自任何来源的设置，包括命令行，ClickOnce URL参数等):

public static void LoadFrom(this ApplicationSettingsBase settings, NameValueCollection configuration)
{
    if (configuration != null)
        foreach (string key in configuration.AllKeys)
            if (!String.IsNullOrEmpty(key))
                try
                {
                    settings[key] = configuration.Get(key);
                }
                catch (SettingsPropertyNotFoundException)
                {
                  // handle bad arguments as you wish
                }
}

例子:

Settings.Default.LoadFrom(new NameValueCollection() { { "Setting1", "Value1" }, { "Setting2", "Value2" } });

相当于Python的Join方法:

/// <summary>
/// same as python 'join'
/// </summary>
/// <typeparam name="T">list type</typeparam>
/// <param name="separator">string separator </param>
/// <param name="list">list of objects to be ToString'd</param>
/// <returns>a concatenated list interleaved with separators</returns>
static public string Join<T>(this string separator, IEnumerable<T> list)
{
    var sb = new StringBuilder();
    bool first = true;

    foreach (T v in list)
    {
        if (!first)
            sb.Append(separator);
        first = false;

        if (v != null)
            sb.Append(v.ToString());
    }

    return sb.ToString();
}

我厌倦了乏味的空检查，而拉值从MySqlDataReader，所以:

public static DateTime? GetNullableDateTime(this MySqlDataReader dr, string fieldName)
{
    DateTime? nullDate = null;
    return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? nullDate : dr.GetDateTime(fieldName);
}

public static string GetNullableString(this MySqlDataReader dr, string fieldName)
{
    return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? String.Empty : dr.GetString(fieldName);
}

public static char? GetNullableChar(this MySqlDataReader dr, string fieldName)
{
    char? nullChar = null;
    return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? nullChar : dr.GetChar(fieldName);
}

当然，这可以用于任何SqlDataReader。

hangy和Joe都对如何做到这一点提出了一些很好的意见，我也有机会在不同的环境中实现类似的东西，所以这里是另一个版本:

public static int? GetNullableInt32(this IDataRecord dr, int ordinal)
{
    int? nullInt = null;
    return dr.IsDBNull(ordinal) ? nullInt : dr.GetInt32(ordinal);
}

public static int? GetNullableInt32(this IDataRecord dr, string fieldname)
{
    int ordinal = dr.GetOrdinal(fieldname);
    return dr.GetNullableInt32(ordinal);
}

public static bool? GetNullableBoolean(this IDataRecord dr, int ordinal)
{
    bool? nullBool = null;
    return dr.IsDBNull(ordinal) ? nullBool : dr.GetBoolean(ordinal);
}

public static bool? GetNullableBoolean(this IDataRecord dr, string fieldname)
{
    int ordinal = dr.GetOrdinal(fieldname);
    return dr.GetNullableBoolean(ordinal);
}