我经常用这个…

原始代码:

if (guid != Guid.Empty) return guid;
else return Guid.NewGuid();

新代码:

return guid.NewGuidIfEmpty();

扩展方法:

public static Guid NewGuidIfEmpty(this Guid uuid)
{
    return (uuid != Guid.Empty ? uuid : Guid.NewGuid());
}

每n个字符换行一个字符串。

public static string WrapAt(this string str, int WrapPos)
{
    if (string.IsNullOrEmpty(str))
        throw new ArgumentNullException("str", "Cannot wrap a null string");
    str = str.Replace("\r", "").Replace("\n", "");

    if (str.Length <= WrapPos)
        return str;

    for (int i = str.Length; i >= 0; i--)
        if (i % WrapPos == 0 && i > 0 && i != str.Length)
            str = str.Insert(i, "\r\n");
    return str;
}

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));
    }
}

简单但比“可枚举”更好。范围”,恕我直言:

/// <summary>
/// Replace "Enumerable.Range(n)" with "n.Range()":
/// </summary>
/// <param name="n">iterations</param>
/// <returns>0..n-1</returns>
public static IEnumerable<int> Range(this int n)
{
    for (int i = 0; i < n; i++)
        yield return i;
}

避免参数的解析模式:

public static bool TryParseInt32(this string input, Action<int> action)
{
    int result;
    if (Int32.TryParse(input, out result))
    {
        action(result);
        return true;
    }
    return false;
}

用法:

if (!textBox.Text.TryParseInt32(number => label.Text = SomeMathFunction(number)))
    label.Text = "Please enter a valid integer";

这可以放在codeplex项目中，如果需要的话

在将表单输入放入数据库之前解析表单输入时，这些扩展方法对我来说非常有用

public static int? ToInt(this string input) 
{
    int val;
    if (int.TryParse(input, out val))
        return val;
    return null;
}

public static DateTime? ToDate(this string input)
{
    DateTime val;
    if (DateTime.TryParse(input, out val))
        return val;
    return null;
}

public static decimal? ToDecimal(this string input)
{
    decimal val;
    if (decimal.TryParse(input, out val))
        return val;
    return null;
}