我有一个关于C#泛型和委托的问题:
首先我描述一般问题—我想要一个委托集合,这些委托应该有一个类似的形式,例如,我的所有委托都应该有这样的形式:取两个相同类型的参数,然后返回int.我想建模这些委托的最好方法是使用泛型委托:
public delegate int MyFunctionDel <T> (T a, T b);
但是如何创建具有不同类型的MyFunctionDel集合?我无法宣布:
List<MyFunctionDel <T>> mylist; //Compile error: cannot find type T
其次,这就是我实际上要做的事情.我想做的事可以通过上述问题解决.但是你可以提供其他解决方案.
我写了一个类似集合的结构:它可以保存任何类型的数据.但是结构中的所有数据都应该是相同的类型.不幸的是,由于某些历史原因,这种结构并不通用.该结构具有Compare方法.
但现在我需要为某些特定类型提供定制的比较器.我想要的行为是:如果有一个数据类型,struture使用自定义比较器,否则使用原始的Compare方法.这是我的演示代码:
/*
*This piece of code demonstates my idea, but never works
*/
static class Program
{
[STAThread]
static void Main()
{
MyStructure s = new MyStructure ();
//create a customized comparer using Comparison<T> generic delegate
Comparison <string> myStirngComparer = (x , y)=> {
return -x.CompareTo(y);
};
s.CustomizedComparers[typeof(string)] = myStirngComparer;
System.Console.WriteLine (s.Compare("a" , "b")); //I am expecting the result to be 1
}
}
class MyStructure
{
//For simplicity, I won't put storage related code here
public int Compare (object o1, object o2)
{
//let's suppose o1 and o2 are always of same type
switch (o1.GetType())
{
case TypeCode.Single: return Compare<Single> ((Single)o1 , (Single)o2);
case TypeCode.Double: return Compare<Double> ((Double)o1 , (Double)o2);
case TypeCode.String: return Compare<String> ((String)o1 , (String)o2);
//and so on.....
}
return 0;
}
//NOTE: code below won't work
//But my logic is: use a Dictionary to store a map from "Type" to "Comparison<T>"
//When doing the comparison, we first examine if there exists one Comparison<T> for
//Type T in the Dictionary
//Compile failed here
public Dictionary <Type , Comparison<T> > CustomizedComparers = new Dictionary <Type , Comparison<T> > ();
private int Compare<T> (T a , T b)
{
if (CustomizedComparers.ContainsKey(typeof(T)))
{
Comparison<T> comp = CustomizedComparers[typeof(T)];
return comp (a , b);
}
else return Comparer<T>.Default.Compare(a, b);
}
}
欢迎任何评论,建议和见解!感谢你们.
最佳答案 您可以创建Dictionary< Type,Delegate>并在请求时将委托转换为正确的类型.考虑使用helper类而不是普通的Dictionary< Type,Delegate>:
public class ComparersCollection
{
private readonly Dictionary<Type, Delegate> _comparers =
new Dictionary<Type,Delegate>();
public void OverrideComparison<T>(Comparison<T> comparison)
{
if(comparison == null)
{
_comparers.Remove(typeof(T));
}
else
{
_comparers[typeof(T)] = comparison;
}
}
public Comparison<T> GetComparison<T>()
{
Delegate comparison;
if(_comparers.TryGetValue(typeof(T), out comparison))
{
return (Comparison<T>)comparison;
}
else
{
return Comparer<T>.Default.Compare;
}
}
}
现在你可以使用:
Comparison <string> myStringComparer = (x, y) => -x.CompareTo(y);
s.CustomizedComparers.OverrideComparison(myStringComparer);
和
var comparison = CustomizedComparers.GetComparison<T>();
return comparison(a, b);