How to pass objects into an attribute constructor

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The values into attributes are limited to simple types; for example, basic constants (including strings) and typeof… you can’t use new or other more complex code. In short; you can’t do this. You can give it the type though:

[PropertyValidation(typeof(NullOrEmptyValidatorScheme)]

i.e. the PropertyValidation ctor takes a Type, and use Activator.CreateInstance inside the code to create the object. Note that you should ideally just store the string internally (AssemblyQualifiedName).

From ECMA 334v4:

§24.1.3 Attribute parameter types

The types of positional and named
parameters for an attribute class are
limited to the attribute parameter
types, which are:

  • One of the following types: bool, byte, char,
    double, float, int, long, short, string.
  • The type object.
  • The type System.Type.
  • An enum type, provided it has public accessibility and the
    types in which it is nested (if any)
    also have public accessibility.
  • Single-dimensional arrays of the above
    types.

and

§24.2 Attribute specification

…

An expression E is an
attribute-argument-expression if all
of the following statements are true:

  • The type of E is an attribute
    parameter type (§24.1.3).
  • At compile-time, the value of E can be
    resolved to one of the following:

    • A constant value.
    • A typeof-expression (§14.5.11) specifying a non-generic
      type, a closed constructed type
      (§25.5.2), or an unbound generic type
      (§25.5).
    • A one-dimensional array of
      attribute-argument-expressions.

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