我一直在用这个:

public static void DelimitedAppend(this StringBuilder sb, string value, string delimiter)
{
    if (sb.Length > 0)
        sb.Append(delimiter);
    sb.Append(value);
}

这只是确保当字符串为空时不会插入分隔符。 例如，创建一个以逗号分隔的单词列表:

var farmAnimals = new[] { new { Species = "Dog", IsTasty = false }, new { Species = "Cat", IsTasty = false }, new { Species = "Chicken", IsTasty = true }, };
var soupIngredients = new StringBuilder();
foreach (var edible in farmAnimals.Where(farmAnimal => farmAnimal.IsTasty))
    soupIngredients.DelimitedAppend(edible.Species, ", ");

下面是我们工作代码库中的一个有趣的例子。在作业线程上遍历一个昂贵的lazy-eval枚举对象，并通过一个可观察对象推回结果。

public static IObservable<T> ToAsyncObservable<T>(this IEnumerable<T> @this)
{
    return Observable.Create<T>(observer =>
    {
        var task = new Task(() =>
        {
            try
            {
                @this.Run(observer.OnNext);
                observer.OnCompleted();
            }
            catch (Exception e)
            {
                observer.OnError(e);
            }
        });

        task.Start();

        return () => { };
    });
}

愚蠢的示例:

new DirectoryInfo(@"c:\program files")
    .EnumerateFiles("*", SearchOption.AllDirectories)
    .ToAsyncObservable()
    .BufferWithTime(TimeSpan.FromSeconds(0.5))
    .ObserveOnDispatcher()
    .Subscribe(
        l => Console.WriteLine("{0} received", l.Count),
        () => Console.WriteLine("Done!"));

for (;;)
{
    Thread.Sleep(10);
    Dispatcher.PushFrame(new DispatcherFrame());
}

显然，这个扩展将是无用的，如果你不使用辉煌的响应式扩展!

感谢评论中的Richard，这个扩展方法是不必要的。RX已经有一个扩展方法“tooobservable”，它接受IScheduler。那就用这个吧!

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;
}

当使用键为字符串的字典时，使用不区分大小写的搜索返回现有的键。我们的用例是文件路径。

/// <summary>
/// Gets the key using <paramref name="caseInsensitiveKey"/> from <paramref name="dictionary"/>.
/// </summary>
/// <typeparam name="T">The dictionary value.</typeparam>
/// <param name="dictionary">The dictionary.</param>
/// <param name="caseInsensitiveKey">The case insensitive key.</param>
/// <returns>
/// An existing key; or <see cref="string.Empty"/> if not found.
/// </returns>
public static string GetKeyIgnoringCase<T>(this IDictionary<string, T> dictionary, string caseInsensitiveKey)
{
    if (string.IsNullOrEmpty(caseInsensitiveKey)) return string.Empty;
    foreach (string key in dictionary.Keys)
    {
        if (key.Equals(caseInsensitiveKey, StringComparison.InvariantCultureIgnoreCase))
        {
            return key;
        }
    }
    return string.Empty;
}

一些方便的字符串助手:

用法:

我讨厌不需要的空格尾随或引导字符串，因为字符串可以采取空值，这可能是棘手的，所以我使用这个:

public bool IsGroup { get { return !this.GroupName.IsNullOrTrimEmpty(); } }

这是另一个扩展方法，我使用一个新的验证框架，我正在试验。你可以看到regex扩展，帮助清理凌乱的regex:

public static bool IsRequiredWithLengthLessThanOrEqualNoSpecial(this String str, int length)
{
    return !str.IsNullOrTrimEmpty() &&
        str.RegexMatch(
            @"^[- \r\n\\\.!:*,@$%&""?\(\)\w']{1,{0}}$".RegexReplace(@"\{0\}", length.ToString()),
            RegexOptions.Multiline) == str;
}

来源:

public static class StringHelpers
{
    /// <summary>
    /// Same as String.IsNullOrEmpty except that
    /// it captures the Empty state for whitespace
    /// strings by Trimming first.
    /// </summary>
    public static bool IsNullOrTrimEmpty(this String helper)
    {
        if (helper == null)
            return true;
        else
            return String.Empty == helper.Trim();
    }

    public static int TrimLength(this String helper)
    {
        return helper.Trim().Length;
    }

    /// <summary>
    /// Returns the matched string from the regex pattern. The
    /// groupName is for named group match values in the form (?<name>group).
    /// </summary>
    public static string RegexMatch(this String helper, string pattern, RegexOptions options, string groupName)
    {
        if (groupName.IsNullOrTrimEmpty())
            return Regex.Match(helper, pattern, options).Value;
        else
            return Regex.Match(helper, pattern, options).Groups[groupName].Value;
    }

    public static string RegexMatch(this String helper, string pattern)
    {
        return RegexMatch(helper, pattern, RegexOptions.None, null);
    }

    public static string RegexMatch(this String helper, string pattern, RegexOptions options)
    {
        return RegexMatch(helper, pattern, options, null);
    }

    public static string RegexMatch(this String helper, string pattern, string groupName)
    {
        return RegexMatch(helper, pattern, RegexOptions.None, groupName);
    }

    /// <summary>
    /// Returns true if there is a match from the regex pattern
    /// </summary>
    public static bool IsRegexMatch(this String helper, string pattern, RegexOptions options)
    {
        return helper.RegexMatch(pattern, options).Length > 0;
    }

    public static bool IsRegexMatch(this String helper, string pattern)
    {
        return helper.IsRegexMatch(pattern, RegexOptions.None);
    }

    /// <summary>
    /// Returns a string where matching patterns are replaced by the replacement string.
    /// </summary>
    /// <param name="pattern">The regex pattern for matching the items to be replaced</param>
    /// <param name="replacement">The string to replace matching items</param>
    /// <returns></returns>
    public static string RegexReplace(this String helper, string pattern, string replacement, RegexOptions options)
    {
        return Regex.Replace(helper, pattern, replacement, options);
    }

    public static string RegexReplace(this String helper, string pattern, string replacement)
    {
        return Regex.Replace(helper, pattern, replacement, RegexOptions.None);
    }
}

我喜欢做很多正则表达式，所以我认为这些比添加using语句和额外的代码来处理命名组更容易。

……怎么样?

public static bool IsWinXPOrHigher(this OperatingSystem OS)
{
  return (OS.Platform == PlatformID.Win32NT)
    && ((OS.Version.Major > 5) || ((OS.Version.Major == 5) && (OS.Version.Minor >= 1)));
}

public static bool IsWinVistaOrHigher(this OperatingSystem OS)
{
  return (OS.Platform == PlatformID.Win32NT)
    && (OS.Version.Major >= 6);
}

public static bool IsWin7OrHigher(this OperatingSystem OS)
{
  return (OS.Platform == PlatformID.Win32NT)
    && ((OS.Version.Major > 6) || ((OS.Version.Major == 6) && (OS.Version.Minor >= 1)));
}

public static bool IsWin8OrHigher(this OperatingSystem OS)
{
  return (OS.Platform == PlatformID.Win32NT)
    && ((OS.Version.Major > 6) || ((OS.Version.Major == 6) && (OS.Version.Minor >= 2)));
}

用法:

if (Environment.OSVersion.IsWinXPOrHigher())
{
  // do stuff
}

if (Environment.OSVersion.IsWinVistaOrHigher())
{
  // do stuff
}

if (Environment.OSVersion.IsWin7OrHigher())
{
  // do stuff
}

if (Environment.OSVersion.IsWin8OrHigher())
{
  // do stuff
}