public static class StringHelper
{
    public static String F(this String str, params object[] args)
    {
        return String.Format(str, args);
    }
}

使用:

"Say {0}".F("Hello");

在。net中，有IndexOf和LastIndexOf方法，它们返回String对象中第一个和最后一个匹配项的索引。我有一个扩展方法来获得第n次出现的索引:

public static partial class StringExtensions {

    public static int NthIndexOf(this String str, String match, int occurrence) {
        int i = 1;
        int index = 0;

        while (i <= occurrence && 
            ( index = str.IndexOf(match, index + 1) ) != -1) {

            if (i == occurrence) {
                // Occurrence match found!
                return index;
            }
            i++;
        }

        // Match not found
        return -1;
    }
}

我使用这个扩展方法通常与匿名类型，以获得一个字典ala ruby

public static Dictionary<string, object> ToDictionary(this object o)
{
    var dictionary = new Dictionary<string, object>();

    foreach (var propertyInfo in o.GetType().GetProperties())
    {
        if (propertyInfo.GetIndexParameters().Length == 0)
        {
            dictionary.Add(propertyInfo.Name, propertyInfo.GetValue(o, null));
        }
    }

    return dictionary;
}

你可以使用它

var dummy = new { color = "#000000", width = "100%", id = "myid" };
Dictionary<string, object> dict = dummy.ToDictionary();

用扩展的方法

public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
    foreach (T item in source)
    {
        action(item);
    }
}

你可以做到的

dummy.ToDictionary().ForEach((p) => Console.Write("{0}='{1}' ", p.Key, p.Value));

输出

Color ='#000000' width='100%' id='myid'

http://www.codeplex.com/linqext/

一些工具IEnumerable: ToString(格式)，ToString(函数)和Join(分隔符)。

例如:

var names = new[] { "Wagner", "Francine", "Arthur", "Bernardo" };

names.ToString("Name: {0}\n");
// Name: Wagner
// Name: Francine
// Name: Arthur
// Name: Bernardo

names.ToString(name => name.Length > 6 ? String.Format("{0} ", name) : String.Empty);
// Francine Bernardo

names.Join(" - ");
// Wagner - Francine - Arthur - Bernardo

扩展:

public static string ToString<T>(this IEnumerable<T> self, string format)
{
    return self.ToString(i => String.Format(format, i));
}

public static string ToString<T>(this IEnumerable<T> self, Func<T, object> function)
{
    var result = new StringBuilder();

    foreach (var item in self) result.Append(function(item));

    return result.ToString();
}

public static string Join<T>(this IEnumerable<T> self, string separator)
{
    return String.Join(separator, values: self.ToArray());
}

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