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。
这是ThrowIfNull的另一个实现:
[ThreadStatic]
private static string lastMethodName = null;
[ThreadStatic]
private static int lastParamIndex = 0;
[MethodImpl(MethodImplOptions.NoInlining)]
public static void ThrowIfNull<T>(this T parameter)
{
var currentStackFrame = new StackFrame(1);
var props = currentStackFrame.GetMethod().GetParameters();
if (!String.IsNullOrEmpty(lastMethodName)) {
if (currentStackFrame.GetMethod().Name != lastMethodName) {
lastParamIndex = 0;
} else if (lastParamIndex >= props.Length - 1) {
lastParamIndex = 0;
} else {
lastParamIndex++;
}
} else {
lastParamIndex = 0;
}
if (!typeof(T).IsValueType) {
for (int i = lastParamIndex; i < props.Length; i++) {
if (props[i].ParameterType.IsValueType) {
lastParamIndex++;
} else {
break;
}
}
}
if (parameter == null) {
string paramName = props[lastParamIndex].Name;
throw new ArgumentNullException(paramName);
}
lastMethodName = currentStackFrame.GetMethod().Name;
}
它不像其他实现那样高效，但有更干净的用法:
public void Foo()
{
Bar(1, 2, "Hello", "World"); //no exception
Bar(1, 2, "Hello", null); //exception
Bar(1, 2, null, "World"); //exception
}
public void Bar(int x, int y, string someString1, string someString2)
{
//will also work with comments removed
//x.ThrowIfNull();
//y.ThrowIfNull();
someString1.ThrowIfNull();
someString2.ThrowIfNull();
//Do something incredibly useful here!
}
改变参数为int?也会起作用。
那
有时使用自定义分隔符在列表中选中的元素上写出字符串是很方便的。
例如，如果你有一个List<Person>并且想要用逗号分隔姓氏，你可以这样做。
string result = string.Empty;
foreach (var person in personList) {
result += person.LastName + ", ";
}
result = result.Substring(0, result.Length - 2);
return result;
或者你可以使用这个方便的扩展方法
public static string Join<T>(this IEnumerable<T> collection, Func<T, string> func, string separator)
{
return String.Join(separator, collection.Select(func).ToArray());
}
像这样使用它
personList.Join(x => x.LastName, ", ");
这将产生相同的结果，在本例中是由逗号分隔的姓氏列表。
这是ThrowIfNull的另一个实现:
[ThreadStatic]
private static string lastMethodName = null;
[ThreadStatic]
private static int lastParamIndex = 0;
[MethodImpl(MethodImplOptions.NoInlining)]
public static void ThrowIfNull<T>(this T parameter)
{
var currentStackFrame = new StackFrame(1);
var props = currentStackFrame.GetMethod().GetParameters();
if (!String.IsNullOrEmpty(lastMethodName)) {
if (currentStackFrame.GetMethod().Name != lastMethodName) {
lastParamIndex = 0;
} else if (lastParamIndex >= props.Length - 1) {
lastParamIndex = 0;
} else {
lastParamIndex++;
}
} else {
lastParamIndex = 0;
}
if (!typeof(T).IsValueType) {
for (int i = lastParamIndex; i < props.Length; i++) {
if (props[i].ParameterType.IsValueType) {
lastParamIndex++;
} else {
break;
}
}
}
if (parameter == null) {
string paramName = props[lastParamIndex].Name;
throw new ArgumentNullException(paramName);
}
lastMethodName = currentStackFrame.GetMethod().Name;
}
它不像其他实现那样高效，但有更干净的用法:
public void Foo()
{
Bar(1, 2, "Hello", "World"); //no exception
Bar(1, 2, "Hello", null); //exception
Bar(1, 2, null, "World"); //exception
}
public void Bar(int x, int y, string someString1, string someString2)
{
//will also work with comments removed
//x.ThrowIfNull();
//y.ThrowIfNull();
someString1.ThrowIfNull();
someString2.ThrowIfNull();
//Do something incredibly useful here!
}
改变参数为int?也会起作用。
那
我使用这个扩展方法通常与匿名类型，以获得一个字典ala ruby
public static Dictionary<string, object> ToDictionary(this object o)
{
var dictionary = new Dictionary<string, object>();
foreach (var propertyInfo in o.GetType().GetProperties())
{
if (propertyInfo.GetIndexParameters().Length == 0)
{
dictionary.Add(propertyInfo.Name, propertyInfo.GetValue(o, null));
}
}
return dictionary;
}
你可以使用它
var dummy = new { color = "#000000", width = "100%", id = "myid" };
Dictionary<string, object> dict = dummy.ToDictionary();
用扩展的方法
public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
foreach (T item in source)
{
action(item);
}
}
你可以做到的
dummy.ToDictionary().ForEach((p) => Console.Write("{0}='{1}' ", p.Key, p.Value));
输出
Color ='#000000' width='100%' id='myid'
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.
