问题描述

//Get PropertyDescriptor object for the given property name
var propDesc = TypeDescriptor.GetProperties(typeof(T))[propName];

//Get FillAttributes methodinfo delegate
var methodInfo = propDesc.GetType().GetMethods(BindingFlags.Instance | BindingFlags.Public |
                                                      BindingFlags.NonPublic)
    .FirstOrDefault(m => m.IsFamily || m.IsPublic && m.Name == "FillAttributes");

//Create Validation attribute
var attribute = new RequiredAttribute();
var  attributes= new ValidationAttribute[]{attribute};

//Invoke FillAttribute method
methodInfo.Invoke(propDesc, new object[] { attributes });

您好，我正在尝试使用上述代码在运行时添加 Validation 属性.但是我得到以下异常:

Hi I am trying to add Validation attribute at runtime using the above code. However I am getting the below exception:

集合的大小是固定的

推荐答案

不要让别人告诉你你做不到.如果你愿意，你可以竞选总统:-)

Don't let someone tell you that you can't do it. You can run for president if you want :-)

为方便起见，这是一个完整的示例

For your convenience, this is a fully working example

public class SomeAttribute : Attribute
{
    public SomeAttribute(string value)
    {
        this.Value = value;
    }

    public string Value { get; set; }
}

public class SomeClass
{
    public string Value = "Test";
}

[TestMethod]
public void CanAddAttribute()
{
    var type = typeof(SomeClass);

    var aName = new System.Reflection.AssemblyName("SomeNamespace");
    var ab = AppDomain.CurrentDomain.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Run);
    var mb = ab.DefineDynamicModule(aName.Name);
    var tb = mb.DefineType(type.Name + "Proxy", System.Reflection.TypeAttributes.Public, type);

    var attrCtorParams = new Type[] { typeof(string) };
    var attrCtorInfo = typeof(SomeAttribute).GetConstructor(attrCtorParams);
    var attrBuilder = new CustomAttributeBuilder(attrCtorInfo, new object[] { "Some Value" });
    tb.SetCustomAttribute(attrBuilder);

    var newType = tb.CreateType();
    var instance = (SomeClass)Activator.CreateInstance(newType);

    Assert.AreEqual("Test", instance.Value);
    var attr = (SomeAttribute)instance.GetType()
        .GetCustomAttributes(typeof(SomeAttribute), false)
        .SingleOrDefault();
    Assert.IsNotNull(attr);
    Assert.AreEqual(attr.Value, "Some Value");
}

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