我开始真的喜欢扩展方法... 我正在想是否有人在这里发现了真正令人惊叹或聪明的例子。
我今天写的一个例子：
由于其他用户的评论而编辑：
public static IEnumerable<int> To(this int fromNumber, int toNumber) {
while (fromNumber < toNumber) {
yield return fromNumber;
fromNumber++;
}
}
这样可以将 for 循环写成 foreach 循环：
foreach (int x in 0.To(16)) {
Console.WriteLine(Math.Pow(2, x).ToString());
}
我迫不及待地想看到其他的例子！祝你愉快！
对int类型做扩展方法，将一个位掩码解码为星期几的枚举（在此情况下，第一天为星期一）：
public static IEnumerable<DayOfWeek> Days(this int dayMask)
{
if ((dayMask & 1) > 0) yield return DayOfWeek.Monday;
if ((dayMask & 2) > 0) yield return DayOfWeek.Tuesday;
if ((dayMask & 4) > 0) yield return DayOfWeek.Wednesday;
if ((dayMask & 8) > 0) yield return DayOfWeek.Thursday;
if ((dayMask & 16) > 0) yield return DayOfWeek.Friday;
if ((dayMask & 32) > 0) yield return DayOfWeek.Saturday;
if ((dayMask & 64) > 0) yield return DayOfWeek.Sunday;
}
这个代码创建了一个数组，并在开头添加了一个元素：
public static T[] Prepend<T>(this T[] array, T item)
{
T[] result = new T[array.Length + 1];
result[0] = item;
Array.Copy(array, 0, result, 1, array.Length);
return result;
}
string[] some = new string[] { "foo", "bar" };
...
some = some.Prepend("baz");
这个函数可以帮助我将某些表达式转换为它们的平方：
public static double Sq(this double arg)
{
return arg * arg;
}
(x - x0).Sq() + (y - y0).Sq() + (z - z0).Sq()
这是我写的另一个：
public static class StringExtensions
{
/// <summary>
/// Returns a Subset string starting at the specified start index and ending and the specified end
/// index.
/// </summary>
/// <param name="s">The string to retrieve the subset from.</param>
/// <param name="startIndex">The specified start index for the subset.</param>
/// <param name="endIndex">The specified end index for the subset.</param>
/// <returns>A Subset string starting at the specified start index and ending and the specified end
/// index.</returns>
public static string Subsetstring(this string s, int startIndex, int endIndex)
{
if (startIndex < 0) throw new ArgumentOutOfRangeException("startIndex", "Must be positive.");
if (endIndex < 0) throw new ArgumentOutOfRangeException("endIndex", "Must be positive.");
if (startIndex > endIndex) throw new ArgumentOutOfRangeException("endIndex", "Must be >= startIndex.");
return s.Substring(startIndex, (endIndex - startIndex));
}
/// <summary>
/// Finds the specified Start Text and the End Text in this string instance, and returns a string
/// containing all the text starting from startText, to the begining of endText. (endText is not
/// included.)
/// </summary>
/// <param name="s">The string to retrieve the subset from.</param>
/// <param name="startText">The Start Text to begin the Subset from.</param>
/// <param name="endText">The End Text to where the Subset goes to.</param>
/// <param name="ignoreCase">Whether or not to ignore case when comparing startText/endText to the string.</param>
/// <returns>A string containing all the text starting from startText, to the begining of endText.</returns>
public static string Subsetstring(this string s, string startText, string endText, bool ignoreCase)
{
if (string.IsNullOrEmpty(startText)) throw new ArgumentNullException("startText", "Must be filled.");
if (string.IsNullOrEmpty(endText)) throw new ArgumentNullException("endText", "Must be filled.");
string temp = s;
if (ignoreCase)
{
temp = s.ToUpperInvariant();
startText = startText.ToUpperInvariant();
endText = endText.ToUpperInvariant();
}
int start = temp.IndexOf(startText);
int end = temp.IndexOf(endText, start);
return Subsetstring(s, start, end);
}
}
string s = "This is a tester for my cool extension method!!";
s = s.Subsetstring("tester", "cool",true);
我主要使用几个扩展。第一组是对象扩展，主要用于转换。
public static class ObjectExtension
{
public static T As<T>(this object value)
{
return (value != null && value is T) ? (T)value : default(T);
}
public static int AsInt(this string value)
{
if (value.HasValue())
{
int result;
var success = int.TryParse(value, NumberStyles.Integer, CultureInfo.InvariantCulture, out result);
if (success)
{
return result;
}
}
return 0;
}
public static Guid AsGuid(this string value)
{
return value.HasValue() ? new Guid(value) : Guid.Empty;
}
}
字符串扩展
public static class StringExtension
{
public static bool HasValue(this string value)
{
return string.IsNullOrEmpty(value) == false;
}
public static string Slug(this string value)
{
if (value.HasValue())
{
var builder = new StringBuilder();
var slug = value.Trim().ToLower();
foreach (var c in slug)
{
switch (c)
{
case ' ':
builder.Append("-");
break;
case '&':
builder.Append("and");
break;
default:
if ((c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') && c != '-')
{
builder.Append(c);
}
break;
}
}
return builder.ToString();
}
return string.Empty;
}
public static string Truncate(this string value, int limit)
{
return (value.Length > limit) ? string.Concat(value.Substring(0, Math.Min(value.Length, limit)), "...") : value;
}
}
最后是一些枚举扩展
public static class EnumExtensions
{
public static bool Has<T>(this Enum source, params T[] values)
{
var value = Convert.ToInt32(source, CultureInfo.InvariantCulture);
foreach (var i in values)
{
var mask = Convert.ToInt32(i, CultureInfo.InvariantCulture);
if ((value & mask) == 0)
{
return false;
}
}
return true;
}
public static bool Has<T>(this Enum source, T values)
{
var value = Convert.ToInt32(source, CultureInfo.InvariantCulture);
var mask = Convert.ToInt32(values, CultureInfo.InvariantCulture);
return (value & mask) != 0;
}
public static T Add<T>(this Enum source, T v)
{
var value = Convert.ToInt32(source, CultureInfo.InvariantCulture);
var mask = Convert.ToInt32(v, CultureInfo.InvariantCulture);
return Enum.ToObject(typeof(T), value | mask).As<T>();
}
public static T Remove<T>(this Enum source, T v)
{
var value = Convert.ToInt32(source, CultureInfo.InvariantCulture);
var mask = Convert.ToInt32(v, CultureInfo.InvariantCulture);
return Enum.ToObject(typeof(T), value & ~mask).As<T>();
}
public static T AsEnum<T>(this string value)
{
try
{
return Enum.Parse(typeof(T), value, true).As<T>();
}
catch
{
return default(T);
}
}
}
很酷，也喜欢扩展！
这里有几个。
这个将会得到一个月的最后一天日期：
<System.Runtime.CompilerServices.Extension()> _
Public Function GetLastMonthDay(ByVal Source As DateTime) As DateTime
Dim CurrentMonth As Integer = Source.Month
Dim MonthCounter As Integer = Source.Month
Dim LastDay As DateTime
Dim DateCounter As DateTime = Source
LastDay = Source
Do While MonthCounter = CurrentMonth
DateCounter = DateCounter.AddDays(1)
MonthCounter = DateCounter.Month
If MonthCounter = CurrentMonth Then
LastDay = DateCounter
End If
Loop
Return LastDay
End Function
这两个工具使得反射变得更加容易：
<System.Runtime.CompilerServices.Extension()> _
Public Function GetPropertyValue(Of ValueType)(ByVal Source As Object, ByVal PropertyName As String) As ValueType
Dim pInfo As System.Reflection.PropertyInfo
pInfo = Source.GetType.GetProperty(PropertyName)
If pInfo Is Nothing Then
Throw New Exception("Property " & PropertyName & " does not exists for object of type " & Source.GetType.Name)
Else
Return pInfo.GetValue(Source, Nothing)
End If
End Function
<System.Runtime.CompilerServices.Extension()> _
Public Function GetPropertyType(ByVal Source As Object, ByVal PropertyName As String) As Type
Dim pInfo As System.Reflection.PropertyInfo
pInfo = Source.GetType.GetProperty(PropertyName)
If pInfo Is Nothing Then
Throw New Exception("Property " & PropertyName & " does not exists for object of type " & Source.GetType.Name)
Else
Return pInfo.PropertyType
End If
End Function
这里有几个我使用过的：
if( enumVar.IsSet( MyEnum.PossibleFlag ) ) //..then
myObject.IfNotNull( x => x.Property );
其中一些已经发布过了，但我想说我看到了很多这样的帖子，投票结果从来不符合实际的有用性。在我看来，以下是真正最有用的扩展方法列表。
someCollection.ForEach(i => i.DoSomething());
这非常有用，因为它替代了内置的foreach语句，我们都知道它经常被使用。
7.CreateSequence();
myCollection.Where(i => i.Something == somethingElse).Count().CreateSequence(). do something else
接下来最有用的是CastTo和As。它们再次复制了内置功能，但它们保留了从左到右的顺序。请注意，CastTo与Cast不同，因为CastTo仅适用于单个对象。
myObject.CastTo<Person>().DoSomething()
myObject.As<Person>()
然后还有SplitAsEnumerable。它的工作方式与split相同，但不会一次性将所有内容加载到内存中。这对于解析大型文件非常有用。它可以在字符串或流上使用。
myFileStream.SplitAsEnumerable("\r\n").Select(line => line.SplitAsEnumerable(","))
myTextBox.Text = "Top 3 scorers are " + myCollection.OrderBy(i => i.Score).Take(3).FlattenToString(i => i.Score.ToString(), ", ");
比较给定文件信息类的任何属性与另一个文件信息类的属性。
public static bool compare(this FileInfo F1,FileInfo F2,string propertyName)
{
try
{
System.Reflection.PropertyInfo p1 = F1.GetType().GetProperty(propertyName);
System.Reflection.PropertyInfo p2 = F2.GetType().GetProperty(propertyName);
if (p1.GetValue(F1, null) == p2.GetValue(F1, null))
{
return true;
}
}
catch (Exception ex)
{
return false;
}
return false;
}
for(int x=0; x<=16; ++x)对有经验的程序员来说更易读。但是，闭区间往往较少使用。 - Tom Hawtin - tackline