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。
这是另一双我觉得用不完的鞋:
public static T ObjectWithMin<T, TResult>(this IEnumerable<T> sequence, Func<T, TResult> predicate)
where T : class
where TResult : IComparable
{
if (!sequence.Any()) return null;
//get the first object with its predicate value
var seed = sequence.Select(x => new {Object = x, Value = predicate(x)}).FirstOrDefault();
//compare against all others, replacing the accumulator with the lesser value
//tie goes to first object found
return
sequence.Select(x => new {Object = x, Value = predicate(x)})
.Aggregate(seed,(acc, x) => acc.Value.CompareTo(x.Value) <= 0 ? acc : x).Object;
}
public static T ObjectWithMax<T, TResult>(this IEnumerable<T> sequence, Func<T, TResult> predicate)
where T : class
where TResult : IComparable
{
if (!sequence.Any()) return null;
//get the first object with its predicate value
var seed = sequence.Select(x => new {Object = x, Value = predicate(x)}).FirstOrDefault();
//compare against all others, replacing the accumulator with the greater value
//tie goes to last object found
return
sequence.Select(x => new {Object = x, Value = predicate(x)})
.Aggregate(seed, (acc, x) => acc.Value.CompareTo(x.Value) > 0 ? acc : x).Object;
}
用法:
var myObject = myList.ObjectWithMin(x=>x.PropA);
这些方法基本上取代了像
var myObject = myList.OrderBy(x=>x.PropA).FirstOrDefault(); //O(nlog(n)) and unstable
and
var myObject = myList.Where(x=>x.PropA == myList.Min(x=>x.PropA)).FirstOrDefault(); //O(N^2) but stable
and
var minValue = myList.Min(x=>x.PropA);
var myObject = myList.Where(x=>x.PropA == minValue).FirstOrDefault(); //not a one-liner, and though linear and stable it's slower (evaluates the enumerable twice)
用于winforms填充组合框:
List<MyObject> myObjects = new List<MyObject>() {
new MyObject() {Name = "a", Id = 0},
new MyObject() {Name = "b", Id = 1},
new MyObject() {Name = "c", Id = 2} }
comboBox.FillDataSource<MyObject>(myObjects, x => x.Name);
扩展方法:
/** <summary>Fills the System.Windows.Forms.ComboBox object DataSource with a
* list of T objects.</summary>
* <param name="values">The list of T objects.</param>
* <param name="displayedValue">A function to apply to each element to get the
* display value.</param>
*/
public static void FillDataSource<T>(this ComboBox comboBox, List<T> values,
Func<T, String> displayedValue) {
// Create dataTable
DataTable data = new DataTable();
data.Columns.Add("ValueMember", typeof(T));
data.Columns.Add("DisplayMember");
for (int i = 0; i < values.Count; i++) {
// For each value/displayed value
// Create new row with value & displayed value
DataRow dr = data.NewRow();
dr["ValueMember"] = values[i];
dr["DisplayMember"] = displayedValue(values[i]) ?? "";
// Add row to the dataTable
data.Rows.Add(dr);
}
// Bind datasource to the comboBox
comboBox.DataSource = data;
comboBox.ValueMember = "ValueMember";
comboBox.DisplayMember = "DisplayMember";
}
您可能已经知道扩展方法的一个有趣用法是作为一种mixin。一些扩展方法,比如XmlSerializable,几乎污染了所有类;这对大多数人来说没有意义,比如Thread和SqlConnection。
一些功能应该显式地混合到希望拥有它的类中。我对这种类型提出了一种新的表示法,以M为前缀。
XmlSerializable是这样的:
public interface MXmlSerializable { }
public static class XmlSerializable {
public static string ToXml(this MXmlSerializable self) {
if (self == null) throw new ArgumentNullException();
var serializer = new XmlSerializer(self.GetType());
using (var writer = new StringWriter()) {
serializer.Serialize(writer, self);
return writer.GetStringBuilder().ToString();
}
}
public static T FromXml<T>(string xml) where T : MXmlSerializable {
var serializer = new XmlSerializer(typeof(T));
return (T)serializer.Deserialize(new StringReader(xml));
}
}
然后一个类将其混合:
public class Customer : MXmlSerializable {
public string Name { get; set; }
public bool Preferred { get; set; }
}
用法很简单:
var customer = new Customer {
Name = "Guybrush Threepwood",
Preferred = true };
var xml = customer.ToXml();
如果您喜欢这个想法,您可以在项目中为有用的mixin创建一个新的名称空间。你怎么看?
哦,顺便说一下,我认为大多数扩展方法都应该显式地测试null。
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();
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, ", ");