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)。

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;
}

这是我写的唯一一个我经常使用的扩展。 它使得用System.Net.Mail发送电子邮件更容易一些。

public static class MailExtension
{
    // GetEmailCreditial(out strServer) gets credentials from an XML file
    public static void Send(this MailMessage email)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        client.Send(email);
    }

    public static void Send(this IEnumerable<MailMessage> emails)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        foreach (MailMessage email in emails)
            client.Send(email);
    }
}

// Example of use: 
new MailMessage("info@myDomain.com","you@gmail.com","This is an important Subject", "Body goes here").Send();
//Assume email1,email2,email3 are MailMessage objects
new List<MailMessage>(){email1, email2, email}.Send();

字符串。As<T>，可用于将字符串值转换为某种类型(主要用于支持IConvertable的原语和类型)。工作伟大的空类型，甚至枚举!

public static partial class StringExtensions
{
    /// <summary>
    /// Converts the string to the specified type, using the default value configured for the type.
    /// </summary>
    /// <typeparam name="T">Type the string will be converted to. The type must implement IConvertable.</typeparam>
    /// <param name="original">The original string.</param>
    /// <returns>The converted value.</returns>
    public static T As<T>(this String original)
    {
        return As(original, CultureInfo.CurrentCulture,
                  default(T));
    }

    /// <summary>
    /// Converts the string to the specified type, using the default value configured for the type.
    /// </summary>
    /// <typeparam name="T">Type the string will be converted to.</typeparam>
    /// <param name="original">The original string.</param>
    /// <param name="defaultValue">The default value to use in case the original string is null or empty, or can't be converted.</param>
    /// <returns>The converted value.</returns>
    public static T As<T>(this String original, T defaultValue)
    {
        return As(original, CultureInfo.CurrentCulture, defaultValue);
    }

    /// <summary>
    /// Converts the string to the specified type, using the default value configured for the type.
    /// </summary>
    /// <typeparam name="T">Type the string will be converted to.</typeparam>
    /// <param name="original">The original string.</param>
    /// <param name="provider">Format provider used during the type conversion.</param>
    /// <returns>The converted value.</returns>
    public static T As<T>(this String original, IFormatProvider provider)
    {
        return As(original, provider, default(T));
    }

    /// <summary>
    /// Converts the string to the specified type.
    /// </summary>
    /// <typeparam name="T">Type the string will be converted to.</typeparam>
    /// <param name="original">The original string.</param>
    /// <param name="provider">Format provider used during the type conversion.</param>
    /// <param name="defaultValue">The default value to use in case the original string is null or empty, or can't be converted.</param>
    /// <returns>The converted value.</returns>
    /// <remarks>
    /// If an error occurs while converting the specified value to the requested type, the exception is caught and the default is returned. It is strongly recommended you
    /// do NOT use this method if it is important that conversion failures are not swallowed up.
    ///
    /// This method is intended to be used to convert string values to primatives, not for parsing, converting, or deserializing complex types.
    /// </remarks>
    public static T As<T>(this String original, IFormatProvider provider,
                          T defaultValue)
    {
        T result;
        Type type = typeof (T);

        if (String.IsNullOrEmpty(original)) result = defaultValue;
        else
        {
            // need to get the underlying type if T is Nullable<>.

            if (type.IsNullableType())
            {
                type = Nullable.GetUnderlyingType(type);
            }

            try
            {
                // ChangeType doesn't work properly on Enums
                result = type.IsEnum
                             ? (T) Enum.Parse(type, original, true)
                             : (T) Convert.ChangeType(original, type, provider);
            }
            catch // HACK: what can we do to minimize or avoid raising exceptions as part of normal operation? custom string parsing (regex?) for well-known types? it would be best to know if you can convert to the desired type before you attempt to do so.
            {
                result = defaultValue;
            }
        }

        return result;
    }
}

这依赖于Type的另一个简单扩展:

/// <summary>
/// Extension methods for <see cref="Type"/>.
/// </summary>
public static class TypeExtensions
{
    /// <summary>
    /// Returns whether or not the specified type is <see cref="Nullable{T}"/>.
    /// </summary>
    /// <param name="type">A <see cref="Type"/>.</param>
    /// <returns>True if the specified type is <see cref="Nullable{T}"/>; otherwise, false.</returns>
    /// <remarks>Use <see cref="Nullable.GetUnderlyingType"/> to access the underlying type.</remarks>
    public static bool IsNullableType(this Type type)
    {
        if (type == null) throw new ArgumentNullException("type");

        return type.IsGenericType && type.GetGenericTypeDefinition().Equals(typeof (Nullable<>));
    }
}

用法:

var someInt = "1".As<int>();
var someIntDefault = "bad value".As(1); // "bad value" won't convert, so the default value 1 is returned.
var someEnum = "Sunday".As<DayOfWeek>();
someEnum = "0".As<DayOfWeek>(); // returns Sunday
var someNullableEnum = "".As<DayOfWeek?>(null); // returns a null value since "" can't be converted

我创建了一个扩展方法来在下拉菜单中选择一个项目。

下面是代码

 public static class Utilities
{
    public enum DropDownListSelectionType
    {
        ByValue,
        ByText
    }

    public static void SelectItem(this  System.Web.UI.WebControls.DropDownList drp, string selectedValue, DropDownListSelectionType type)
    {
        drp.ClearSelection();
        System.Web.UI.WebControls.ListItem li;
        if (type == DropDownListSelectionType.ByValue)
            li = drp.Items.FindByValue(selectedValue.Trim());
        else
            li = drp.Items.FindByText(selectedValue.Trim());
        if (li != null)
            li.Selected = true;
    }}

此方法可以由以下代码行调用，以按文本进行选择

DropDownList1.SelectItem("ABCD", Utilities.DropDownListSelectionType.ByText);

或者按值选择

DropDownList1.SelectItem("11", Utilities.DropDownListSelectionType.ByValue);

上面的代码不选择任何东西，如果它不能找到传递进来的文本/值。

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, ", ");