[英]Creating an performant open delegate for an property setter or getter
open delegate是沒有目標的實例方法的委托。 要調用它,您需要提供目標作為其第一個參數。 它們是優化代碼的一種聰明方法,否則會使用反射並且性能較差。 有關開放代表的介紹,請參閱此內容 。 你在實踐中使用它的方法是使用昂貴的反射代碼來構建這些開放的委托,但是你可以像一個簡單的委托調用一樣非常便宜地調用它們。
我正在嘗試編寫將任意PropertyInfo轉換為其setter的委托的代碼。 到目前為止,我想出了這個:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
namespace Test
{
class TestClass
{
static Action<T, object> MakeSetterDelegate<T>(PropertyInfo property)
{
MethodInfo setMethod = property.GetSetMethod();
if (setMethod != null && setMethod.GetParameters().Length == 1) //skips over nasty index properties
{
//To be able to bind to the delegate we have to create a delegate
//type like: Action<T,actualType> rather than Action<T,object>.
//We use reflection to do that
Type setterGenericType = typeof(Action<,>);
Type delegateType = setterGenericType.MakeGenericType(new Type[] { typeof(T), property.PropertyType });
var untypedDelegate = Delegate.CreateDelegate(delegateType, setMethod);
//we wrap the Action<T,actualType> delegate into an Action<T,object>
Action<T, object> setter = (instance, value) =>
{
untypedDelegate.DynamicInvoke(new object[] { instance, value });
};
return setter;
}
else
{
return null;
}
}
int TestProp
{
set
{
System.Diagnostics.Debug.WriteLine("Called set_TestProp");
}
}
static void Test()
{
PropertyInfo property = typeof(TestClass).GetProperty("TestProp");
Action<TestClass, object> setter = MakeSetterDelegate<TestClass>(property);
TestClass instance = new TestClass();
setter(instance, 5);
}
}
}
將為getter編寫類似的代碼。 它可以工作,但是setter委托使用DynamicInvoke從Action <derivedType
>轉換為Action <object
>,我懷疑它正在吃掉我所追求的優化的很大一部分。 所以問題是:
DynamicInvoke
不會創建高性能的setter。 反對泛型內部類型的反射在這里是更好的選擇,因為這將允許您使用類型化的委托。 另一個選項是DynamicMethod
,但是你需要擔心一些IL細節。
您可能希望查看HyperDescriptor
,它將IL工作包裝到PropertyDescriptor
實現中。 另一個選項是Expression
API(如果您使用的是.NET 3.5或更高版本):
static Action<T, object> MakeSetterDelegate<T>(PropertyInfo property)
{
MethodInfo setMethod = property.GetSetMethod();
if (setMethod != null && setMethod.GetParameters().Length == 1)
{
var target = Expression.Parameter(typeof(T));
var value = Expression.Parameter(typeof(object));
var body = Expression.Call(target, setMethod,
Expression.Convert(value, property.PropertyType));
return Expression.Lambda<Action<T, object>>(body, target, value)
.Compile();
}
else
{
return null;
}
}
或者使用通用類型:
abstract class Setter<T>
{
public abstract void Set(T obj, object value);
}
class Setter<TTarget, TValue> : Setter<TTarget>
{
private readonly Action<TTarget, TValue> del;
public Setter(MethodInfo method)
{
del = (Action<TTarget, TValue>)
Delegate.CreateDelegate(typeof(Action<TTarget, TValue>), method);
}
public override void Set(TTarget obj, object value)
{
del(obj, (TValue)value);
}
}
static Action<T, object> MakeSetterDelegate<T>(PropertyInfo property)
{
MethodInfo setMethod = property.GetSetMethod();
if (setMethod != null && setMethod.GetParameters().Length == 1)
{
Setter<T> untyped = (Setter<T>) Activator.CreateInstance(
typeof(Setter<,>).MakeGenericType(typeof(T),
property.PropertyType), setMethod);
return untyped.Set;
}
else
{
return null;
}
}
我曾經上過這堂課。 也許它有幫助:
public class GetterSetter<EntityType,propType>
{
private readonly Func<EntityType, propType> getter;
private readonly Action<EntityType, propType> setter;
private readonly string propertyName;
private readonly Expression<Func<EntityType, propType>> propertyNameExpression;
public EntityType Entity { get; set; }
public GetterSetter(EntityType entity, Expression<Func<EntityType, propType>> property_NameExpression)
{
Entity = entity;
propertyName = GetPropertyName(property_NameExpression);
propertyNameExpression = property_NameExpression;
//Create Getter
getter = propertyNameExpression.Compile();
// Create Setter()
MethodInfo method = typeof (EntityType).GetProperty(propertyName).GetSetMethod();
setter = (Action<EntityType, propType>)
Delegate.CreateDelegate(typeof(Action<EntityType, propType>), method);
}
public propType Value
{
get
{
return getter(Entity);
}
set
{
setter(Entity, value);
}
}
protected string GetPropertyName(LambdaExpression _propertyNameExpression)
{
var lambda = _propertyNameExpression as LambdaExpression;
MemberExpression memberExpression;
if (lambda.Body is UnaryExpression)
{
var unaryExpression = lambda.Body as UnaryExpression;
memberExpression = unaryExpression.Operand as MemberExpression;
}
else
{
memberExpression = lambda.Body as MemberExpression;
}
var propertyInfo = memberExpression.Member as PropertyInfo;
return propertyInfo.Name;
}
測試:
var gs = new GetterSetter<OnOffElement,bool>(new OnOffElement(), item => item.IsOn);
gs.Value = true;
var result = gs.Value;
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