Change Attribute's parameter at runtime

Well you learn something new every day, apparently I lied:

What isn’t generally realised is that you can change attribute instance values fairly easily at runtime. The reason is, of course, that the instances of the attribute classes that are created are perfectly normal objects and can be used without restriction. For example, we can get the object:

ASCII[] attrs1=(ASCII[])
    typeof(MyClass).GetCustomAttributes(typeof(ASCII), false);

…change the value of its public variable and show that it has changed:

attrs1[0].MyData="A New String";
MessageBox.Show(attrs1[0].MyData);

…and finally create another instance and show that its value is unchanged:

ASCII[] attrs3=(ASCII[])
    typeof(MyClass).GetCustomAttributes(typeof(ASCII), false);
 MessageBox.Show(attrs3[0].MyData);

http://www.vsj.co.uk/articles/display.asp?id=713

In case anyone else walks down this avenue, the answer is you can do it, with reflection, except you can't because there's a bug in the framework. Here's how you would do it:

Dim prop As PropertyDescriptor = TypeDescriptor.GetProperties(GetType(UserInfo))("Age")
Dim att As CategoryAttribute = DirectCast(prop.Attributes(GetType(CategoryAttribute)), CategoryAttribute)
Dim cat As FieldInfo = att.GetType.GetField("categoryValue", BindingFlags.NonPublic Or BindingFlags.Instance)
cat.SetValue(att, "A better description")

All well and good, except that the category attribute is changed for all the properties, not just 'Age'.

Did you solve the problem?

Here are possible steps to achieve an acceptable solution.

1. Try to create a child class, redefine all of the properties that you need to change the [Category] attribute (mark them with new). Example:

public class UserInfo
{
 [Category("Must change")]
 public string Name { get; set; }
}

public class NewUserInfo : UserInfo
{
 public NewUserInfo(UserInfo user)
 {
 // transfer all the properties from user to current object
 }

 [Category("Changed")]
 public new string Name {
get {return base.Name; }
set { base.Name = value; }
 }

public static NewUserInfo GetNewUser(UserInfo user)
{
return NewUserInfo(user);
}
}

void YourProgram()
{
UserInfo user = new UserInfo();
...

// Bind propertygrid to object

grid.DataObject = NewUserInfo.GetNewUser(user);

...

}

Later Edit: This part of the solution is not workable if you have a large number of properties that you might need to rewrite the attributes. This is where part two comes into place:

2. Of course, this won't help if the class is not inheritable, or if you have a lot of objects (and properties). You would need to create a full automatic proxy class that gets your class and creates a dynamic class, applies attributes and of course makes a connection between the two classes.. This is a little more complicated, but also achievable. Just use reflection and you're on the right road.

I really don't think so, unless there's some funky reflection that can pull it off. The property decorations are set at compile time and to my knowledge are fixed

In the mean time I've come to a partial solution, derived from the following articles:

1. ICustomTypeDescriptor, Part 1
2. ICustomTypeDescriptor, Part 2
3. Add (Remove) Items to (from) PropertyGrid at Runtime

Basically you would create a generic class CustomTypeDescriptorWithResources<T>, that would get the properties through reflection and load Description and Category from a file (I suppose you need to display localized text so you could use a resources file (.resx))

You can change Attribute values at runtime at Class level (not object):

var attr = TypeDescriptor.GetProperties(typeof(UserContact))["UserName"].Attributes[typeof(ReadOnlyAttribute)] as ReadOnlyAttribute;
attr.GetType().GetField("isReadOnly", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(attr, username_readonly);