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。
一些用于使用列表的扩展:
/// <summary>
/// Wrap an object in a list
/// </summary>
public static IList<T> WrapInList<T>(this T item)
{
List<T> result = new List<T>();
result.Add(item);
return result;
}
使用如:
myList = someObject.InList();
使IEnumerable包含来自一个或多个源的项,以使IEnumerable更像列表。对于高性能代码来说,这可能不是一个好主意,但对于测试来说很有用:
public static IEnumerable<T> Append<T>(this IEnumerable<T> enumerable, T newItem)
{
foreach (T item in enumerable)
{
yield return item;
}
yield return newItem;
}
public static IEnumerable<T> Append<T>(this IEnumerable<T> enumerable, params T[] newItems)
{
foreach (T item in enumerable)
{
yield return item;
}
foreach (T newItem in newItems)
{
yield return newItem;
}
}
如使用。
someEnumeration = someEnumeration.Append(newItem);
还有其他可能的变化——例如。
someEnumeration = someEnumeration.Append(otherEnumeration);
如果你正在克隆项目,你可能还想克隆它们的列表:
public static IList<T> Clone<T>(this IEnumerable<T> source) where T: ICloneable
{
List<T> result = new List<T>();
foreach (T item in source)
{
result.Add((T)item.Clone());
}
return result;
}
当我使用ObservableCollection<T>时,我通常使用AddRange方法扩展它。这里的其他答案给出了这个的实现。
如果您愿意,可以将此代码放入Codeplex项目中。
我厌倦了乏味的空检查,而拉值从MySqlDataReader,所以:
public static DateTime? GetNullableDateTime(this MySqlDataReader dr, string fieldName)
{
DateTime? nullDate = null;
return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? nullDate : dr.GetDateTime(fieldName);
}
public static string GetNullableString(this MySqlDataReader dr, string fieldName)
{
return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? String.Empty : dr.GetString(fieldName);
}
public static char? GetNullableChar(this MySqlDataReader dr, string fieldName)
{
char? nullChar = null;
return dr.IsDBNull(dr.GetOrdinal(fieldName)) ? nullChar : dr.GetChar(fieldName);
}
当然,这可以用于任何SqlDataReader。
hangy和Joe都对如何做到这一点提出了一些很好的意见,我也有机会在不同的环境中实现类似的东西,所以这里是另一个版本:
public static int? GetNullableInt32(this IDataRecord dr, int ordinal)
{
int? nullInt = null;
return dr.IsDBNull(ordinal) ? nullInt : dr.GetInt32(ordinal);
}
public static int? GetNullableInt32(this IDataRecord dr, string fieldname)
{
int ordinal = dr.GetOrdinal(fieldname);
return dr.GetNullableInt32(ordinal);
}
public static bool? GetNullableBoolean(this IDataRecord dr, int ordinal)
{
bool? nullBool = null;
return dr.IsDBNull(ordinal) ? nullBool : dr.GetBoolean(ordinal);
}
public static bool? GetNullableBoolean(this IDataRecord dr, string fieldname)
{
int ordinal = dr.GetOrdinal(fieldname);
return dr.GetNullableBoolean(ordinal);
}
// This file contains extension methods for generic List<> class to operate on sorted lists.
// Duplicate values are OK.
// O(ln(n)) is still much faster then the O(n) of LINQ's searches/filters.
static partial class SortedList
{
// Return the index of the first element with the key greater then provided.
// If there's no such element within the provided range, it returns iAfterLast.
public static int sortedFirstGreaterIndex<tElt, tKey>( this IList<tElt> list, Func<tElt, tKey, int> comparer, tKey key, int iFirst, int iAfterLast )
{
if( iFirst < 0 || iAfterLast < 0 || iFirst > list.Count || iAfterLast > list.Count )
throw new IndexOutOfRangeException();
if( iFirst > iAfterLast )
throw new ArgumentException();
if( iFirst == iAfterLast )
return iAfterLast;
int low = iFirst, high = iAfterLast;
// The code below is inspired by the following article:
// http://en.wikipedia.org/wiki/Binary_search#Single_comparison_per_iteration
while( low < high )
{
int mid = ( high + low ) / 2;
// 'mid' might be 'iFirst' in case 'iFirst+1 == iAfterLast'.
// 'mid' will never be 'iAfterLast'.
if( comparer( list[ mid ], key ) <= 0 ) // "<=" since we gonna find the first "greater" element
low = mid + 1;
else
high = mid;
}
return low;
}
// Return the index of the first element with the key greater then the provided key.
// If there's no such element, returns list.Count.
public static int sortedFirstGreaterIndex<tElt, tKey>( this IList<tElt> list, Func<tElt, tKey, int> comparer, tKey key )
{
return list.sortedFirstGreaterIndex( comparer, key, 0, list.Count );
}
// Add an element to the sorted array.
// This could be an expensive operation if frequently adding elements that sort firstly.
// This is cheap operation when adding elements that sort near the tail of the list.
public static int sortedAdd<tElt>( this List<tElt> list, Func<tElt, tElt, int> comparer, tElt elt )
{
if( list.Count == 0 || comparer( list[ list.Count - 1 ], elt ) <= 0 )
{
// either the list is empty, or the item is greater then all elements already in the collection.
list.Add( elt );
return list.Count - 1;
}
int ind = list.sortedFirstGreaterIndex( comparer, elt );
list.Insert( ind, elt );
return ind;
}
// Find first exactly equal element, return -1 if not found.
public static int sortedFindFirstIndex<tElt, tKey>( this List<tElt> list, Func<tElt, tKey, int> comparer, tKey elt )
{
int low = 0, high = list.Count - 1;
while( low < high )
{
int mid = ( high + low ) / 2;
if( comparer( list[ mid ], elt ) < 0 )
low = mid + 1;
else
high = mid; // this includes the case when we've found an element exactly matching the key
}
if( high >= 0 && 0 == comparer( list[ high ], elt ) )
return high;
return -1;
}
// Return the IEnumerable that returns array elements in the reverse order.
public static IEnumerable<tElt> sortedReverse<tElt>( this List<tElt> list )
{
for( int i=list.Count - 1; i >= 0; i-- )
yield return list[ i ];
}
}
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;
}