随着实体的概念的流行,DataTable正在逐渐的淡出我们的视野,但是,有些时候,DataTable很容易做的一件事情,却让我们不得不头痛起来——按指定列排序
如果数据是来源于一个sql语句,那么,我们可以把这个问题转嫁给sql,让DB来解决这个问题。
但是,如果数据来源于某些不支持排序(例如webservice并且没有提供排序功能),或者其他复杂情况,这样就不得不依赖于.net的集合排序。可是,如果一个系统有10个这样的类,平均每个类有10个属性可能被选择,那么就意味着有100个排序方法需要被写(c#3.0的Lambda表达式当然可以为我们省下很多力气)。如果,有一个方法直接输入属性的名称,就返回一个按照对应属性的比较器,岂不是更容易?
基于这个想法,再加上效率的考量,用Emit写了简单的单一属性的使用默认比较器的排序:
![](https://www.cnblogs.com/Images/OutliningIndicators/ContractedBlock.gif)
Code
1
public static class Extensions
2![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
{
3
public static void SortByProperty<T>(this T[] array, string propName)
4![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
5
Array.Sort(array, Inner<T>.GetComparison(propName));
6
}
7![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
8
public static void SortByProperty<T>(this List<T> list, string propName)
9![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
10
list.Sort(Inner<T>.GetComparison(propName));
11
}
12![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
13
private static class Inner<T>
14![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
15
private static Dictionary<string, Comparison<T>> m_cache =
16
new Dictionary<string, Comparison<T>>();
17![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
18
internal static Comparison<T> GetComparison(string propName)
19![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
20
Comparison<T> comparison;
21
if (!m_cache.TryGetValue(propName, out comparison))
22
m_cache[propName] = comparison = GetComparisonNoCache(propName);
23
return comparison;
24
}
25![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
26
private static Comparison<T> GetComparisonNoCache(string propName)
27![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
28
bool isValueType = typeof(T).IsValueType;
29
var prop = typeof(T).GetProperty(propName);
30
var comparerType = typeof(Comparer<>).MakeGenericType(prop.PropertyType);
31
DynamicMethod dm = new DynamicMethod(string.Empty, typeof(int),
32![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
new Type[]
{ typeof(T), typeof(T) }, typeof(T));
33
var il = dm.GetILGenerator();
34
il.Emit(OpCodes.Call, comparerType.GetProperty("Default").GetGetMethod());
35
if (isValueType)
36![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
37
il.Emit(OpCodes.Ldarga_S, 0);
38
il.Emit(OpCodes.Call, prop.GetGetMethod());
39
il.Emit(OpCodes.Ldarga_S, 1);
40
il.Emit(OpCodes.Call, prop.GetGetMethod());
41
}
42
else
43![](https://www.cnblogs.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
{
44
il.Emit(OpCodes.Ldarg_0);
45
il.Emit(OpCodes.Callvirt, prop.GetGetMethod());
46
il.Emit(OpCodes.Ldarg_1);
47
il.Emit(OpCodes.Callvirt, prop.GetGetMethod());
48
}
49
il.Emit(OpCodes.Callvirt, comparerType.GetMethod("Compare"));
50
il.Emit(OpCodes.Ret);
51
return (Comparison<T>)dm.CreateDelegate(typeof(Comparison<T>));
52
}
53
}
54
}
55![](https://www.cnblogs.com/Images/OutliningIndicators/None.gif)
因为,考虑到经常需要排序可空类型(例如:int?),所以,使用Comparer<T>.Default的Compare方法,当然性能上略有损失,在属性是int的情况下,与直接用Lambda相比,性能大概是5:6,也就是说在数组相对比较大时,如果用Lambda需要5s,那么用这个方法可能就需要6s。功能上来说,由于无法传入比较器,排序功能上比较弱,只能应付用属性的默认比较器的排序的情况。