我想出了一種方法,但它基本上需要一些反思魔術來解決它。
/// <summary>
/// Converts the delegate to <see cref="TDelegate"/>, provided the types are compatible. Can use
/// variance of delegate typing in .NET 4 for a speedy conversion. Otherwise, uses Delegate.CreateDelegate
/// to create a new delegate with the appropriate signature.
/// </summary>
/// <typeparam name="TDelegate">The target delegate type.</typeparam>
/// <param name="delegate">The @delegate.</param>
/// <returns></returns>
public static TDelegate ConvertDelegate<TDelegate>(Delegate @delegate) where TDelegate : class
{
ArgumentValidator.AssertIsNotNull(() => @delegate);
var targetType = typeof(TDelegate);
ArgumentValidator.AssertIsDelegateType(() => targetType);
var currentType = @delegate.GetType();
if (targetType.IsAssignableFrom(currentType))
{
return @delegate as TDelegate; // let's skip as much of this as we can.
}
var currentMethod = currentType.GetMethod("Invoke");
var targetMethod = targetType.GetMethod("Invoke");
if (!AreDelegateInvokeMethodsCompatible(currentMethod, targetMethod, true))
{
throw new ArgumentException(string.Format("{0} is incompatible with {1}.", currentType, targetType), ExpressionHelper.GetMemberName(() => @delegate));
}
var invocationList = @delegate.GetInvocationList();
return DelegateHelper.Combine(@delegate.GetInvocationList()
.Select(d => IsMethodRunTimeGenerated(d.Method) ?
GetDynamicMethodFromMethodInfo(d.Method).CreateDelegate<TDelegate>(d.Target) :
DelegateHelper.CreateDelegate<TDelegate>(d.Target, d.Method)).ToArray());
}
#region Private Static Variables
private static Type s_RTDynamicMethodType = Type.GetType("System.Reflection.Emit.DynamicMethod+RTDynamicMethod",false,true);
private static Func<MethodInfo, DynamicMethod> s_GetDynamicMethodDelegate = CreateGetDynamicMethodDelegate();
#endregion Private Static Variables
private static Func<MethodInfo, DynamicMethod> CreateGetDynamicMethodDelegate()
{
var param = Expression.Parameter(
typeof(MethodInfo),
typeof(MethodInfo).Name
);
var expression = Expression.Lambda<Func<MethodInfo, DynamicMethod>>(
Expression.Field(
Expression.Convert(
param,
s_RTDynamicMethodType
),
s_RTDynamicMethodType.GetField("m_owner", BindingFlags.NonPublic | BindingFlags.Instance)
),
param
);
return expression.Compile();
}
我不會離開我的委託幫助類,除非別人真的需要它。但重要的是它是可能的,而且非常快。轉換時間通常小於1毫秒,幾乎不像瞬時方法組轉換那麼快,但您知道這是一些東西。
您確定'var'代碼在.net 3.5中不起作用,但它在.net 4中工作?任何錯誤消息? – 2010-10-13 04:15:38
@Danny:委託類型不支持C#3.0中的協變和反變換。 – 2010-10-13 05:00:55
如果有一種方法可以在C#3.0中進行委託方差,那麼我們不需要在C#4.0中添加*特性;它已經實施了。我認爲你運氣不好。 – 2010-10-13 05:02:06