让我们把你的优秀和最喜欢的扩展方法列一个列表。

要求是必须发布完整的代码,以及如何使用它的示例和解释。

基于对这个主题的高度兴趣,我在Codeplex上建立了一个名为extensionoverflow的开源项目。

请将您的回答标记为接受,以便将代码放入Codeplex项目。

请张贴完整的源代码,而不是一个链接。

Codeplex上新闻:

24.08.2010 Codeplex页面现在在这里:http://extensionoverflow.codeplex.com/

11.11.2008 XmlSerialize / XmlDeserialize现在是实现和单元测试。

11.11.2008仍有发展空间。;-)现在就加入!

11.11.2008第三位贡献者加入了ExtensionOverflow,欢迎加入BKristensen

11.11.2008 FormatWith现在是实现和单元测试。

09.11.2008第二个贡献者加入ExtensionOverflow。欢迎来到chakrit。

我们需要更多的开发人员。: -)

09.11.2008 ThrowIfArgumentIsNull现已在Codeplex上实现和单元测试。


当前回答

我发现自己一遍又一遍地这样做……

public static bool EqualsIgnoreCase(this string a, string b)
{
    return string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
}

...然后是StartsWithIgnoreCase, EndsWithIgnoreCase和ContainsIgnoreCase。

其他回答

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!

没有检查整个线程,所以它可能已经在这里,但是:

public static class FluentOrderingExtensions
    public class FluentOrderer<T> : IEnumerable<T>
    {
        internal List<Comparison<T>> Comparers = new List<Comparison<T>>();

        internal IEnumerable<T> Source;

        public FluentOrderer(IEnumerable<T> source)
        {
            Source = source;
        }

        #region Implementation of IEnumerable

        public IEnumerator<T> GetEnumerator()
        {
            var workingArray = Source.ToArray();
            Array.Sort(workingArray, IterativeComparison);

            foreach(var element in workingArray) yield return element;
        }

        private int IterativeComparison(T a, T b)
        {
            foreach (var comparer in Comparers)
            {
                var result = comparer(a,b);
                if(result != 0) return result;
            }
            return 0;
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        #endregion
    }

    public static FluentOrderer<T> OrderFluentlyBy<T,TResult>(this IEnumerable<T> source, Func<T,TResult> predicate) 
        where TResult : IComparable<TResult>
    {
        var result = new FluentOrderer<T>(source);
        result.Comparers.Add((a,b)=>predicate(a).CompareTo(predicate(b)));
        return result;
    }

    public static FluentOrderer<T> OrderFluentlyByDescending<T,TResult>(this IEnumerable<T> source, Func<T,TResult> predicate) 
        where TResult : IComparable<TResult>
    {
        var result = new FluentOrderer<T>(source);
        result.Comparers.Add((a,b)=>predicate(a).CompareTo(predicate(b)) * -1);
        return result;
    }

    public static FluentOrderer<T> ThenBy<T, TResult>(this FluentOrderer<T> source, Func<T, TResult> predicate)
        where TResult : IComparable<TResult>
    {
        source.Comparers.Add((a, b) => predicate(a).CompareTo(predicate(b)));
        return source;
    }

    public static FluentOrderer<T> ThenByDescending<T, TResult>(this FluentOrderer<T> source, Func<T, TResult> predicate)
        where TResult : IComparable<TResult>
    {
        source.Comparers.Add((a, b) => predicate(a).CompareTo(predicate(b)) * -1);
        return source;
    }
}

用法:

var myFluentlyOrderedList = GetABunchOfComplexObjects()
    .OrderFluentlyBy(x=>x.PropertyA)
    .ThenByDescending(x=>x.PropertyB)
    .ThenBy(x=>x.SomeMethod())
    .ThenBy(x=>SomeOtherMethodAppliedTo(x))
    .ToList();

... 当然,假设所有的谓词都返回与自身icomcomparable的类型。如果使用像MergeSort这样的稳定排序,而不是。net内置的快速排序,它会更好地工作,但它提供了类似于SQL的可读多字段排序能力(无论如何,它是方法链所能获得的最接近的功能)。您可以通过定义重载来接受比较lambda,而不是基于谓词创建它,从而扩展它以容纳非IComparable的成员。

EDIT: A little explanation, since the commenter got some upticks: this set of methods improves upon the basic OrderBy() functionality by allowing you to sort based on multiple fields in descending order of importance. A real-world example would be sorting a list of invoices by customer, then by invoice number (or invoice date). Other methods of getting the data in this order either wouldn't work (OrderBy() uses an unstable sort, so it cannot be chained) or would be inefficient and not look like it does what you're trying to do.

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();

比较两个对象的相等性,而不必重写Equals或实现IEquatable<>。

你为什么要这么做?当你真的想知道两个对象是否相等,但你懒得重写Equals(object)或实现IEquatable<T>。或者,更现实地说,如果您有一个非常复杂的类,手工实现Equals将非常乏味、容易出错,维护起来也不有趣。如果您不太关心性能,它也会有所帮助。

我目前使用IsEqualTo是因为第二个原因——我有一个具有许多属性的类,这些属性的类型是其他用户定义的类,每个类都有许多其他属性,这些属性的类型是其他用户定义的类,一直到无限。在许多这样的类中加入一堆集合,实现Equals(object)真的变成了一场噩梦。

用法:

if (myTerriblyComplexObject.IsEqualTo(myOtherTerriblyComplexObject))
{
    // Do something terribly interesting.
}

为了确定相等,我做了很多比较。我尽一切努力按照“正确”的顺序做“正确”的事。比较顺序如下:

Use the static Equals(object, object) method. If it returns true, return true. It will return true if the references are the same. It will also return true if thisObject overrides Equals(object). If thisObject is null, return false. No further comparisons can be made if it is null. If thisObject has overridden Equals(object), return false. Since it overrides Equals, it must mean that Equals was executed at step #1 and returned false. If someone has bothered to override Equals, we should respect that and return what Equals returns. If thisObject inherits from IEquatable<T>, where otherObject can be assigned to T, get the Equals(T) method using reflection. Invoke that method and return its return value. If both objects are IEnumerable, return whether contain the same items, in the same order, using IsEqualTo to compare the items. If the objects have different types, return false. Since we know now that thisObject does not have an Equals method, there isn't any way to realistically evaluate two object of different types to be true. If the objects are a value type (primitive or struct) or a string, return false. We have already failed the Equals(object) test - enough said. For each property of thisObject, test its value with IsEqualTo. If any return false, return false. If all return true, return true.

字符串比较可能更好,但很容易实现。此外,我不能100%确定我处理结构正确。

话不多说,下面是扩展方法:

/// <summary>
/// Provides extension methods to determine if objects are equal.
/// </summary>
public static class EqualsEx
{
    /// <summary>
    /// The <see cref="Type"/> of <see cref="string"/>.
    /// </summary>
    private static readonly Type StringType = typeof(string);

    /// <summary>
    /// The <see cref="Type"/> of <see cref="object"/>.
    /// </summary>
    private static readonly Type ObjectType = typeof(object);

    /// <summary>
    /// The <see cref="Type"/> of <see cref="IEquatable{T}"/>.
    /// </summary>
    private static readonly Type EquatableType = typeof(IEquatable<>);

    /// <summary>
    /// Determines whether <paramref name="thisObject"/> is equal to <paramref name="otherObject"/>.
    /// </summary>
    /// <param name="thisObject">
    /// This object.
    /// </param>
    /// <param name="otherObject">
    /// The other object.
    /// </param>
    /// <returns>
    /// True, if they are equal, otherwise false.
    /// </returns>
    public static bool IsEqualTo(this object thisObject, object otherObject)
    {
        if (Equals(thisObject, otherObject))
        {
            // Always check Equals first. If the object has overridden Equals, use it. This will also capture the case where both are the same reference.
            return true;
        }

        if (thisObject == null)
        {
            // Because Equals(object, object) returns true if both are null, if either is null, return false.
            return false;
        }

        var thisObjectType = thisObject.GetType();
        var equalsMethod = thisObjectType.GetMethod("Equals", BindingFlags.Public | BindingFlags.Instance, null, new[] { ObjectType }, null);
        if (equalsMethod.DeclaringType == thisObjectType)
        {
            // thisObject overrides Equals, and we have already failed the Equals test, so return false.
            return false;
        }

        var otherObjectType = otherObject == null ? null : otherObject.GetType();

        // If thisObject inherits from IEquatable<>, and otherObject can be passed into its Equals method, use it.
        var equatableTypes = thisObjectType.GetInterfaces().Where(                                          // Get interfaces of thisObjectType that...
            i => i.IsGenericType                                                                            // ...are generic...
            && i.GetGenericTypeDefinition() == EquatableType                                                // ...and are IEquatable of some type...
            && (otherObjectType ==  null || i.GetGenericArguments()[0].IsAssignableFrom(otherObjectType))); // ...and otherObjectType can be assigned to the IEquatable's type.

        if (equatableTypes.Any())
        {
            // If we found any interfaces that meed our criteria, invoke the Equals method for each interface.
            // If any return true, return true. If all return false, return false.
            return equatableTypes
                .Select(equatableType => equatableType.GetMethod("Equals", BindingFlags.Public | BindingFlags.Instance))
                .Any(equatableEqualsMethod => (bool)equatableEqualsMethod.Invoke(thisObject, new[] { otherObject }));
        }

        if (thisObjectType != StringType && thisObject is IEnumerable && otherObject is IEnumerable)
        {
            // If both are IEnumerable, check their items.
            var thisEnumerable = ((IEnumerable)thisObject).Cast<object>();
            var otherEnumerable = ((IEnumerable)otherObject).Cast<object>();

            return thisEnumerable.SequenceEqual(otherEnumerable, IsEqualToComparer.Instance);
        }

        if (thisObjectType != otherObjectType)
        {
            // If they have different types, they cannot be equal.
            return false;
        }

        if (thisObjectType.IsValueType || thisObjectType == StringType)
        {
            // If it is a value type, we have already determined that they are not equal, so return false.
            return false;
        }

        // Recurse into each public property: if any are not equal, return false. If all are true, return true.
        return !(from propertyInfo in thisObjectType.GetProperties()
                 let thisPropertyValue = propertyInfo.GetValue(thisObject, null)
                 let otherPropertyValue = propertyInfo.GetValue(otherObject, null)
                 where !thisPropertyValue.IsEqualTo(otherPropertyValue)
                 select thisPropertyValue).Any();
    }

    /// <summary>
    /// A <see cref="IEqualityComparer{T}"/> to be used when comparing sequences of collections.
    /// </summary>
    private class IsEqualToComparer : IEqualityComparer<object>
    {
        /// <summary>
        /// The singleton instance of <see cref="IsEqualToComparer"/>.
        /// </summary>
        public static readonly IsEqualToComparer Instance;

        /// <summary>
        /// Initializes static members of the <see cref="EqualsEx.IsEqualToComparer"/> class.
        /// </summary>
        static IsEqualToComparer()
        {
            Instance = new IsEqualToComparer();
        }

        /// <summary>
        /// Prevents a default instance of the <see cref="EqualsEx.IsEqualToComparer"/> class from being created.
        /// </summary>
        private IsEqualToComparer()
        {
        }

        /// <summary>
        /// Determines whether the specified objects are equal.
        /// </summary>
        /// <param name="x">
        /// The first object to compare.
        /// </param>
        /// <param name="y">
        /// The second object to compare.
        /// </param>
        /// <returns>
        /// true if the specified objects are equal; otherwise, false.
        /// </returns>
        bool IEqualityComparer<object>.Equals(object x, object y)
        {
            return x.IsEqualTo(y);
        }

        /// <summary>
        /// Not implemented - throws an <see cref="NotImplementedException"/>.
        /// </summary>
        /// <param name="obj">
        /// The <see cref="object"/> for which a hash code is to be returned.
        /// </param>
        /// <returns>
        /// A hash code for the specified object.
        /// </returns>
        int IEqualityComparer<object>.GetHashCode(object obj)
        {
            throw new NotImplementedException();
        }
    }
}

我创建了一个漂亮的Each扩展,具有与jQuery的Each函数相同的行为。

它允许如下所示,你可以获得当前值的索引,并通过返回false跳出循环:

new[] { "first", "second", "third" }.Each((value, index) =>
{
    if (value.Contains("d"))
        return false;
    Console.Write(value);
    return true;
});

下面是代码

/// <summary>
/// Generic iterator function that is useful to replace a foreach loop with at your discretion.  A provided action is performed on each element.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="action">Function that takes in the current value in the sequence. 
/// <returns></returns>
public static IEnumerable<T> Each<T>(this IEnumerable<T> source, Action<T> action)
{
    return source.Each((value, index) =>
    {
        action(value);
        return true;
    });
}


/// <summary>
/// Generic iterator function that is useful to replace a foreach loop with at your discretion.  A provided action is performed on each element.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="action">Function that takes in the current value and its index in the sequence.  
/// <returns></returns>
public static IEnumerable<T> Each<T>(this IEnumerable<T> source, Action<T, int> action)
{
    return source.Each((value, index) =>
    {
        action(value, index);
        return true;
    });
}

/// <summary>
/// Generic iterator function that is useful to replace a foreach loop with at your discretion.  A provided action is performed on each element.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="action">Function that takes in the current value in the sequence.  Returns a value indicating whether the iteration should continue.  So return false if you don't want to iterate anymore.</param>
/// <returns></returns>
public static IEnumerable<T> Each<T>(this IEnumerable<T> source, Func<T, bool> action)
{
    return source.Each((value, index) =>
    {
        return action(value);
    });
}

/// <summary>
/// Generic iterator function that is useful to replace a foreach loop with at your discretion.  A provided action is performed on each element.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="action">Function that takes in the current value and its index in the sequence.  Returns a value indicating whether the iteration should continue.  So return false if you don't want to iterate anymore.</param>
/// <returns></returns>
public static IEnumerable<T> Each<T>(this IEnumerable<T> source, Func<T, int, bool> action)
{
    if (source == null)
        return source;

    int index = 0;
    foreach (var sourceItem in source)
    {
        if (!action(sourceItem, index))
            break;
        index++;
    }
    return source;
}