如果你有波斯语，并且必须用波斯语向用户显示数字:

static public string ToFaString         (this string value)
        {
            // 1728 , 1584
            string result = "";
            if (value != null)
            {
                char[] resChar = value.ToCharArray();
                for (int i = 0; i < resChar.Length; i++)
                {
                    if (resChar[i] >= '0' && resChar[i] <= '9')
                        result += (char)(resChar[i] + 1728);
                    else
                        result += resChar[i];
                }
            }
            return result;
        }

我使用的两种颜色扩展，主要用于控件开发:

public static class ColorExtensions
{
  // Gets a color that will be readable on top of a given background color
  public static Color GetForegroundColor(this Color input)
  {
    // Math taken from one of the replies to
    // http://stackoverflow.com/questions/2241447/make-foregroundcolor-black-or-white-depending-on-background
    if (Math.Sqrt(input.R * input.R * .241 + input.G * input.G * .691 + input.B * input.B * .068) > 128)
      return Color.Black;
    else
      return Color.White;
  }

  // Converts a given Color to gray
  public static Color ToGray(this Color input)
  {
    int g = (int)(input.R * .299) + (int)(input.G * .587) + (int)(input.B * .114);
    return Color.FromArgb(input.A, g, g, g);
  }
}

用法:

Color foreColor = someBackColor.GetForegroundColor();
Color grayColor = someBackColor.ToGray();

public static bool In<T>(this T source, params T[] list)
{
  if(null==source) throw new ArgumentNullException("source");
  return list.Contains(source);
}

允许我替换:

if(reallyLongIntegerVariableName == 1 || 
    reallyLongIntegerVariableName == 6 || 
    reallyLongIntegerVariableName == 9 || 
    reallyLongIntegerVariableName == 11)
{
  // do something....
}

and

if(reallyLongStringVariableName == "string1" || 
    reallyLongStringVariableName == "string2" || 
    reallyLongStringVariableName == "string3")
{
  // do something....
}

and

if(reallyLongMethodParameterName == SomeEnum.Value1 || 
    reallyLongMethodParameterName == SomeEnum.Value2 || 
    reallyLongMethodParameterName == SomeEnum.Value3 || 
    reallyLongMethodParameterName == SomeEnum.Value4)
{
  // do something....
}

:

if(reallyLongIntegerVariableName.In(1,6,9,11))
{
      // do something....
}

and

if(reallyLongStringVariableName.In("string1","string2","string3"))
{
      // do something....
}

and

if(reallyLongMethodParameterName.In(SomeEnum.Value1, SomeEnum.Value2, SomeEnum.Value3, SomeEnum.Value4)
{
  // do something....
}

gitorious.org/cadenza是我所见过的一些最有用的扩展方法的完整库。

字符串。格式的快捷方式:

public static class StringExtensions
{
    // Enable quick and more natural string.Format calls
    public static string F(this string s, params object[] args)
    {
        return string.Format(s, args);
    }
}

例子:

var s = "The co-ordinate is ({0}, {1})".F(point.X, point.Y);

要快速复制粘贴，请点击这里。

难道你不觉得输入“一些字符串”. f(“param”)而不是字符串更自然吗?格式(“一些字符串”，“参数”)?

想要一个更容易读懂的名字，试试下面的建议:

s = "Hello {0} world {1}!".Fmt("Stack", "Overflow");
s = "Hello {0} world {1}!".FormatBy("Stack", "Overflow");
s = "Hello {0} world {1}!".FormatWith("Stack", "Overflow");
s = "Hello {0} world {1}!".Display("Stack", "Overflow");
s = "Hello {0} world {1}!".With("Stack", "Overflow");

..

另一个对我有用的是:

/// <summary>
/// Converts any type in to an Int32
/// </summary>
/// <typeparam name="T">Any Object</typeparam>
/// <param name="value">Value to convert</param>
/// <returns>The integer, 0 if unsuccessful</returns>
public static int ToInt32<T>(this T value)
{
  int result;
  if (int.TryParse(value.ToString(), out result))
  {
    return result;
  }
  return 0;
}

/// <summary>
/// Converts any type in to an Int32 but if null then returns the default
/// </summary>
/// <param name="value">Value to convert</param>
/// <typeparam name="T">Any Object</typeparam>
/// <param name="defaultValue">Default to use</param>
/// <returns>The defaultValue if unsuccessful</returns>
public static int ToInt32<T>(this T value, int defaultValue)
{
  int result;
  if (int.TryParse(value.ToString(), out result))
  {
    return result;
  }
  return defaultValue;
}

例子:

int number = "123".ToInt32();

or:

int badNumber = "a".ToInt32(100); // Returns 100 since a is nan