从动态生成的类获取属性 [英] Get Attribute from Dynamically generated Class
问题描述
我遇到了一个问题,通常看起来像是相同问题的解决方案都无法解决.
I have run in to a little bit of a problem which is not solved by the generally available solutions to seemingly the same problem.
考虑:
我有一组动态生成的类,它们是从已知的基类继承的(我们称其为 BaseClass
).这些动态生成的类还具有动态生成的具有相关属性的 Properties
.
I have a set of dynamically generated classes, inheriting from a known base Class (lets call it BaseClass
).
These dynamically generated classes also have dynamically generated Properties
with associated attributes.
属性也属于自定义类,尽管不是动态生成的:
The attributes are also of a custom class, though not dynamically generated:
[AttributeUsage(AttributeTargets.Property)]
class TypeAttribute: Attribute
{
private Type _type;
public Type Type
{
get { return _type; }
}
public TypeAttribute(Type t)
{
_type = t;
}
}
然后,我当然想在运行时获取此已分配属性的值:
Then I want to, runtime of course, fetch the value of this assigned attribute:
List<PropertyInfo> result = target.GetType()
.GetProperties()
.Where(
p =>
p.GetCustomAttributes(typeof(TypeAttribute), true)
//.Where(ca => ((TypeAttribute)ca).)
.Any()
)
.ToList();
其中 target
是 BaseClass
的子类.但是,列表结果
为空,这使我感到困惑.
where target
is a subclass of BaseClass
. The List result
is however empty, and this baffles me.
我使用添加属性
PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName,
PropertyAttributes.HasDefault, propertyType, null);
ConstructorInfo classCtorInfo = typeof(TypeAttribute).
GetConstructor(new Type[] { typeof(Type) });
CustomAttributeBuilder myCABuilder = new CustomAttributeBuilder(
classCtorInfo, new object[] { getType(dataType) });
propertyBuilder.SetCustomAttribute(myCABuilder);
其中 dataType
是要存储在属性中的类型,而 tb
是该类的 TypeBuilder
.
where dataType
is the type to store in the attribute and tb
is the TypeBuilder
for the class.
如果我对该属性执行 getCustomAttributes()
,我将获得期望的属性,除了我要查找的属性.但是,如果我执行 getCustomAttributesData()
,我会得到所有的信息,但是我要查找的是类型为 CustomAttributeData
的类型,并且无法转换为 TypeAttribute 代码>(如果我在VS调试器中检查实例,则可以看到其中包含的信息用于
TypeAttribute
).我猜这是问题的征兆,但我找不到原因-更不用说解决了.
If I do getCustomAttributes()
on the property, I get the expected attributes except the one I'm looking for. But if I do getCustomAttributesData()
I get all of them, but the one I'm looking for is of type CustomAttributeData
and is not castable to TypeAttribute
(if i examine the instance in the VS debugger i can see that the contained information is for a TypeAttribute
).
I'm guessing that this is a symptom of the problem, but I cannot find the cause - much less the solution.
有人可以告诉我为什么 result
列表为空吗?
Can anybody point out to me why the result
list is empty?
推荐答案
对我来说很好;您确定您的属性和getter或setter方法存在的程度足以使其实际显示为属性吗?
Works fine for me; are you sure your property and getter or setter method(s) exist sufficiently that it actually shows as a property?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
[AttributeUsage(AttributeTargets.Property)]
public class TypeAttribute : Attribute
{
private Type _type;
public Type Type
{
get { return _type; }
}
public TypeAttribute(Type t)
{
_type = t;
}
}
public class BaseClass
{
}
static class Program
{
static void Main()
{
var aName = new AssemblyName("MyAssembly");
var ab = AppDomain.CurrentDomain.DefineDynamicAssembly(
aName, AssemblyBuilderAccess.RunAndSave);
var mb = ab.DefineDynamicModule(aName.Name, aName.Name + ".dll");
var tb = mb.DefineType("MyType", TypeAttributes.Public, typeof(BaseClass));
var propertyName = "MyProperty";
var propertyType = typeof(int);
var propertyBuilder = tb.DefineProperty(propertyName,
PropertyAttributes.HasDefault, propertyType, null);
var classCtorInfo = typeof(TypeAttribute).
GetConstructor(new Type[] { typeof(Type) });
Type tArg = typeof(float); // for no real reason
var myCABuilder = new CustomAttributeBuilder(
classCtorInfo, new object[] { tArg });
propertyBuilder.SetCustomAttribute(myCABuilder);
var field = tb.DefineField("myField", propertyType, FieldAttributes.Private);
var getter = tb.DefineMethod("get_" + propertyName,
MethodAttributes.HideBySig | MethodAttributes.SpecialName | MethodAttributes.Public,
propertyType, Type.EmptyTypes);
propertyBuilder.SetGetMethod(getter);
var il = getter.GetILGenerator();
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldfld, field);
il.Emit(OpCodes.Ret);
var setter = tb.DefineMethod("set_" + propertyName,
MethodAttributes.HideBySig | MethodAttributes.SpecialName | MethodAttributes.Public,
typeof(void), new[] { typeof(int) });
il = setter.GetILGenerator();
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldarg_1);
il.Emit(OpCodes.Stfld, field);
il.Emit(OpCodes.Ret);
propertyBuilder.SetSetMethod(setter);
var target = Activator.CreateInstance(tb.CreateType());
List<PropertyInfo> result = target.GetType()
.GetProperties()
.Where(
p =>
p.GetCustomAttributes(typeof(TypeAttribute), true)
//.Where(ca => ((TypeAttribute)ca).)
.Any()
).ToList();
}
}
此外,如果只关心它退出,使用 Attribute.IsDefined
会更有效.
Also, it is more efficient to use Attribute.IsDefined
if you just care that it exits.
List<PropertyInfo> result = target.GetType().GetProperties()
.Where(p => Attribute.IsDefined(p, typeof(TypeAttribute), true)).ToList();
还请注意,我不得不欺骗 getType(dataType)
东西-我看不到它在做什么,因为它不是问题所在.确保它返回 Type
.
Note also that I had to spoof the getType(dataType)
stuff - I couldn't see what that was doing as it wasn't in the question. Make sure it returns a Type
.
这篇关于从动态生成的类获取属性的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!