public static class DictionaryExtensions
{
    public static Nullable<TValue> GetValueOrNull<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key)
        where TValue : struct
    {
        TValue result;
        if (dictionary.TryGetValue(key, out result))
            return result;
        else
            return null;
    }
}

免费使用，只需在代码中提到我的名字(Janko Röbisch)。

一些我最好的方法扩展(我有很多!):

public static T ToEnum<T>(this string str) where T : struct
{
    return (T)Enum.Parse(typeof(T), str);
}

//DayOfWeek sunday =  "Sunday".ToEnum<DayOfWeek>();

public static string ToString<T>(this IEnumerable<T> collection, string separator)
{
    return ToString(collection, t => t.ToString(), separator);
}

public static string ToString<T>(this IEnumerable<T> collection, Func<T, string> stringElement, string separator)
{
    StringBuilder sb = new StringBuilder();
    foreach (var item in collection)
    {
        sb.Append(stringElement(item));
        sb.Append(separator);
    }
    return sb.ToString(0, Math.Max(0, sb.Length - separator.Length));  // quita el ultimo separador
}

//new []{1,2,3}.ToString(i=>i*2, ", ")  --> "2, 4, 6"

此外，下一个意味着能够在几乎任何情况下继续在同一行中，而不是声明新变量然后删除状态:

public static R Map<T, R>(this T t, Func<T, R> func)
{
    return func(t);
}

ExpensiveFindWally().Map(wally=>wally.FirstName + " " + wally.LastName)

public static R TryCC<T, R>(this T t, Func<T, R> func)
    where T : class
    where R : class
{
    if (t == null) return null;
    return func(t);
}

public static R? TryCS<T, R>(this T t, Func<T, R> func)
    where T : class
    where R : struct
{
    if (t == null) return null;
    return func(t);
}

public static R? TryCS<T, R>(this T t, Func<T, R?> func)
    where T : class
    where R : struct
{
    if (t == null) return null;
    return func(t);
}

public static R TrySC<T, R>(this T? t, Func<T, R> func)
    where T : struct
    where R : class
{
    if (t == null) return null;
    return func(t.Value);
}

public static R? TrySS<T, R>(this T? t, Func<T, R> func)
    where T : struct
    where R : struct
{
    if (t == null) return null;
    return func(t.Value);
}

public static R? TrySS<T, R>(this T? t, Func<T, R?> func)
    where T : struct
    where R : struct
{
    if (t == null) return null;
    return func(t.Value);
}

//int? bossNameLength =  Departament.Boss.TryCC(b=>b.Name).TryCS(s=>s.Length);


public static T ThrowIfNullS<T>(this T? t, string mensaje)
    where T : struct
{
    if (t == null)
        throw new NullReferenceException(mensaje);
    return t.Value;
}

public static T ThrowIfNullC<T>(this T t, string mensaje)
    where T : class
{
    if (t == null)
        throw new NullReferenceException(mensaje);
    return t;
}

public static T Do<T>(this T t, Action<T> action)
{
    action(t);
    return t;
}

//Button b = new Button{Content = "Click"}.Do(b=>Canvas.SetColumn(b,2));

public static T TryDo<T>(this T t, Action<T> action) where T : class
{
    if (t != null)
        action(t);
    return t;
}

public static T? TryDoS<T>(this T? t, Action<T> action) where T : struct
{
    if (t != null)
        action(t.Value);
    return t;
}

希望它看起来不像来自火星:)

轻松序列化对象为XML:

public static string ToXml<T>(this T obj) where T : class
{
    XmlSerializer s = new XmlSerializer(obj.GetType());
    using (StringWriter writer = new StringWriter())
    {
        s.Serialize(writer, obj);
        return writer.ToString();
    }
}

"<root><child>foo</child</root>".ToXml<MyCustomType>();

这是我今天刚创建的一个。

// requires .NET 4

public static TReturn NullOr<TIn, TReturn>(this TIn obj, Func<TIn, TReturn> func,
        TReturn elseValue = default(TReturn)) where TIn : class
    { return obj != null ? func(obj) : elseValue; }

// versions for CLR 2, which doesn't support optional params

public static TReturn NullOr<TIn, TReturn>(this TIn obj, Func<TIn, TReturn> func,
        TReturn elseValue) where TIn : class
    { return obj != null ? func(obj) : elseValue; }
public static TReturn NullOr<TIn, TReturn>(this TIn obj, Func<TIn, TReturn> func)
        where TIn : class
    { return obj != null ? func(obj) : default(TReturn); }

它让你这样做:

var lname = thingy.NullOr(t => t.Name).NullOr(n => n.ToLower());

哪个比这个更流畅，(依我看)更容易阅读:

var lname = (thingy != null ? thingy.Name : null) != null
    ? thingy.Name.ToLower() : null;

灵感来自弦。IsNullOrEmpty

要验证给定的List为空或空

public static bool IsNullOrEmpty<TSource>(this List<TSource> src)
{            
    return (src == null || src.Count == 0);
}

这个是验证给定的两个文件和属性

public static bool Compare(this FileInfo f1, FileInfo f2, string propertyName)
{
    try
    {
        PropertyInfo p1 = f1.GetType().GetProperty(propertyName);
        PropertyInfo p2 = f2.GetType().GetProperty(propertyName);

        if (p1.GetValue(f1, null) == p2.GetValue(f1, null))
            return true;
    }
    catch (Exception ex)
    {
        return false;
    }
    return false;
}

像这样使用它

FileInfo fo = new FileInfo("c:\\netlog.txt");
FileInfo f1 = new FileInfo("c:\\regkey.txt");

fo.compare(f1, "CreationTime");

与时间跨度相关的扩展，如:

public static TimeSpan Seconds(this int seconds)
{
  return TimeSpan.FromSeconds(seconds);
}

public static TimeSpan Minutes(this int minutes)
{
  return TimeSpan.FromMinutes(minutes);
}

允许使用:

1.Seconds()
20.Minutes()

像这样的锁定扩展:

public static IDisposable GetReadLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterReadLock();
  return new DisposableAction(slimLock.ExitReadLock);
}

public static IDisposable GetWriteLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterWriteLock();
  return new DisposableAction(slimLock.ExitWriteLock);
}

public static IDisposable GetUpgradeableReadLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterUpgradeableReadLock();
  return new DisposableAction(slimLock.ExitUpgradeableReadLock);
}

允许使用像这样的锁:

using (lock.GetUpgradeableReadLock())
{
  // try read
  using (lock.GetWriteLock())
  {
    //do write
  }
}

还有许多来自Lokad共享图书馆的其他书籍