将double类型转换为使用指定区域性格式化的字符串:

public static class ExtensionMethods 
{
  public static string ToCurrency(this double value, string cultureName)
  {
    CultureInfo currentCulture = new CultureInfo(cultureName);
    return (string.Format(currentCulture, "{0:C}", value));
  }
}

例子:

double test = 154.20;
string testString = test.ToCurrency("en-US"); // $154.20

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;
}

这是我经常使用的控件调用扩展;

public static class InvokeExtensions
{
    public static void InvokeHandler(this Control control, MethodInvoker del) // Sync. control-invoke extension.
    {
        if (control.InvokeRequired)
        {
            control.Invoke(del);
            return; 
        }
        del(); // run the actual code.
    }

    public static void AsyncInvokeHandler(this Control control, MethodInvoker del) // Async. control-invoke extension.
    {
        if (control.InvokeRequired)
        {
            control.BeginInvoke(del);
            return; 
        }
        del(); // run the actual code.
    }
}

样本;

this.TreeView.AsyncInvokeHandler(() =>
        {
            this.Text = 'xyz'
        });

允许跨线程gui更新。

IEnumerable < >洗牌

我用Fisher-Yates算法实现了一个shuffle函数。

通过使用yield return和将代码分解为两个函数，它实现了适当的参数验证和延迟执行。(谢谢丹，在我的第一个版本中指出了这个缺陷)

static public IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
{
    if (source == null) throw new ArgumentNullException("source");

    return ShuffleIterator(source);
}

static private IEnumerable<T> ShuffleIterator<T>(this IEnumerable<T> source)
{
    T[] array = source.ToArray();
    Random rnd = new Random();          
    for (int n = array.Length; n > 1;)
    {
        int k = rnd.Next(n--); // 0 <= k < n

        //Swap items
        if (n != k)
        {
            T tmp = array[k];
            array[k] = array[n];
            array[n] = tmp;
        }
    }

    foreach (var item in array) yield return item;
}

我发现自己一遍又一遍地这样做……

public static bool EqualsIgnoreCase(this string a, string b)
{
    return string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
}

.．.然后是StartsWithIgnoreCase, EndsWithIgnoreCase和ContainsIgnoreCase。

把这个:

DbCommand command = connection.CreateCommand();
command.CommandText = "SELECT @param";

DbParameter param = command.CreateParameter();
param.ParameterName = "@param";
param.Value = "Hello World";

command.Parameters.Add(param);

．.． 到这个:

DbCommand command = connection.CreateCommand("SELECT {0}", "Hello World");

．.． 使用这个扩展方法:

using System;
using System.Data.Common;
using System.Globalization;
using System.Reflection;

namespace DbExtensions {

   public static class Db {

      static readonly Func<DbConnection, DbProviderFactory> getDbProviderFactory;
      static readonly Func<DbCommandBuilder, int, string> getParameterName;
      static readonly Func<DbCommandBuilder, int, string> getParameterPlaceholder;

      static Db() {

         getDbProviderFactory = (Func<DbConnection, DbProviderFactory>)Delegate.CreateDelegate(typeof(Func<DbConnection, DbProviderFactory>), typeof(DbConnection).GetProperty("DbProviderFactory", BindingFlags.Instance | BindingFlags.NonPublic).GetGetMethod(true));
         getParameterName = (Func<DbCommandBuilder, int, string>)Delegate.CreateDelegate(typeof(Func<DbCommandBuilder, int, string>), typeof(DbCommandBuilder).GetMethod("GetParameterName", BindingFlags.Instance | BindingFlags.NonPublic, Type.DefaultBinder, new Type[] { typeof(Int32) }, null));
         getParameterPlaceholder = (Func<DbCommandBuilder, int, string>)Delegate.CreateDelegate(typeof(Func<DbCommandBuilder, int, string>), typeof(DbCommandBuilder).GetMethod("GetParameterPlaceholder", BindingFlags.Instance | BindingFlags.NonPublic, Type.DefaultBinder, new Type[] { typeof(Int32) }, null));
      }

      public static DbProviderFactory GetProviderFactory(this DbConnection connection) {
         return getDbProviderFactory(connection);
      }

      public static DbCommand CreateCommand(this DbConnection connection, string commandText, params object[] parameters) {

         if (connection == null) throw new ArgumentNullException("connection");

         return CreateCommandImpl(GetProviderFactory(connection).CreateCommandBuilder(), connection.CreateCommand(), commandText, parameters);
      }

      private static DbCommand CreateCommandImpl(DbCommandBuilder commandBuilder, DbCommand command, string commandText, params object[] parameters) {

         if (commandBuilder == null) throw new ArgumentNullException("commandBuilder");
         if (command == null) throw new ArgumentNullException("command");
         if (commandText == null) throw new ArgumentNullException("commandText");

         if (parameters == null || parameters.Length == 0) {
            command.CommandText = commandText;
            return command;
         }

         object[] paramPlaceholders = new object[parameters.Length];

         for (int i = 0; i < paramPlaceholders.Length; i++) {

            DbParameter dbParam = command.CreateParameter();
            dbParam.ParameterName = getParameterName(commandBuilder, i);
            dbParam.Value = parameters[i] ?? DBNull.Value;
            command.Parameters.Add(dbParam);

            paramPlaceholders[i] = getParameterPlaceholder(commandBuilder, i);
         }

         command.CommandText = String.Format(CultureInfo.InvariantCulture, commandText, paramPlaceholders);

         return command;
      }
   }
}

更多的麻烦。NET扩展方法:DbExtensions