您不能在运行时更改属性。它们被嵌入到程序集的元数据。你的方法是改变一个特定实例的内部状态;但是当你再次加载属性，你得到一个不同的实例。

I need change attribute’s paramater during runtime. I simplified my problem to simple example.

Attribute class:

    [AttributeUsage(AttributeTargets.Property)]
    public class MyAttribute : Attribute
    {
        public string Name { get; set; }
    }

Simple entity wich has decorated properties with attributes:

    public class MyEntity
    {
        [MyAttribute(Name="OldValue1")]
        public string Data1{ get; set; }

        [MyAttribute(Name = "OldValue2")]
        public string Data2 { get; set; }
    }

I created instace of class MyEntity. I can change value of object’s properties, but I can’t change value of attribute’s property Name on object entity. Is it possible?

Value of property on object entity I can change with this part of code:

                entityProp.SetValue(entity,"NewData",null);

but I don’t how change value of attribute’s property Name on object entity

This not work:

attProp.SetValue(attribute,"NewData",null);

Value of propery Name is still original.

Here is all test code. Thank you for hellp.

    [TestMethod]
    public  void Test()
    {
        var entity = new MyEntity
                         {
                             Data1 = "OldData",
                             Data2 = "OldData"
                         };

        PropertyInfo[] entityProps = entity.GetType().GetProperties();

        foreach (var entityProp in entityProps)
        {
            var attribute = Attribute.GetCustomAttribute(entityProp, typeof (MyAttribute)) as MyAttribute;

            if (attribute != null)
            {
                //get attribute’s property NAME
                PropertyInfo attProp= attribute.GetType().GetProperty("Name");

                //get entity property value
                var propertyValue = entityProp.GetValue(entity, null);

                //get attribute’s property NAME value
                var atributeNameValue = attProp.GetValue(entity, null);

                TestContext.WriteLine(string.Format("property name:{0} property value: {1} : atribute name value: {2}\n", 
                    entityProp.Name, propertyValue, atributeNameValue)); 

                //change values
                entityProp.SetValue(entity,"NewData",null);

                //how can I change value of property Name on object entity ?
                attProp.SetValue(attribute,"NewData",null);

            }

        }

        TestContext.WriteLine(string.Format("After change\n"));

        foreach (var entityProp in entityProps)
        {
            var attribute = Attribute.GetCustomAttribute(entityProp, typeof(MyAttribute)) as MyAttribute;

            if (attribute != null)
            {

                PropertyInfo attProp = attribute.GetType().GetProperty("Name");

                var propertyValue = entityProp.GetValue(entity, null);
                var atributeNameValue = attProp.GetValue(entity, null);

                TestContext.WriteLine(string.Format("property name:{0} property value: {1} : atribute name value: {2}\n",
                    entityProp.Name, propertyValue, atributeNameValue));
            }
        }



    }

EDITED: I delete original post and added very simple clear sample. Sorry

You cannot change attributes at runtime. They are embedded into the metadata of the assembly. Your method is changing the internal state of a particular instance; but when you load the attribute again, you are getting a different instance.