How to add an attribute to a property at runtime

Question

//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 }); 

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

Collection was of a fixed size

Answer 1

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

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"); } 

Answer 2

Use FastDeepCloner which I developed.

public class test{     public string Name{ get; set; } }  var prop = DeepCloner.GetFastDeepClonerProperties(typeof(test)).First(); prop.Attributes.Add(new JsonIgnoreAttribute()); // now test and se if exist  prop = DeepCloner.GetFastDeepClonerProperties(typeof(test)).First(); bool containAttr = prop.ContainAttribute<JsonIgnoreAttribute>() // or  JsonIgnoreAttribute myAttr = prop.GetCustomAttribute<JsonIgnoreAttribute>();