How can I pass an attribute parameter type with List<string> in C#?

Question

How can I pass a List to a construtor?

It shows a message:

Error 14 An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

public class CustomAuthorize : AuthorizeAttribute {
    private List<string> multipleProgramID;

    //constructor
    public CustomAuthorize(List<string> _multipleProgramID) {
        multipleProgramID = _multipleProgramID;
    }
}

[CustomAuthorize(new List<string>(new string[] { ProgramList.SURVEY_INPUT, ProgramList.SURVEY_OUTPUT } ))]
[HttpPost]
public ActionResult DeleteWaterQualityItems(string sourceID, string wqID) {
    // ..other code...
}

public class ProgramList {
    public const string SURVEY_INPUT = "A001";
    public const string SURVEY_INPUT = "A002";
}

Answer 1

The problem isn't passing a List<string> to a constructor in general - the problem is that you're trying to use it for an attribute . You basically can't do that, because it's not a compile-time constant.

It looks like ProgramList is effectively an enum - so you might want to make it an enum instead:

 [Flags]
 public enum ProgramLists
 {
     SurveyInput,
     SurveyOutput,
     ...
 }

Then make your CustomAuthorizeAttribute (which should be named like that, with a suffix of Attribute ) accept a ProgramLists in the constructor. You'd specify it as:

[CustomAuthorize(ProgramLists.SurveyInput | ProgramLists.SurveyOutput)]

You can then have a separate way of mapping each ProgramLists element to a string such as "A001" . This could be done by applying an attribute to each element, or maybe having a Dictionary<ProgramLists, string> somewhere.

If you really want to keep using strings like this, you could make CustomAuthorizeAttribute accept a single comma-separated list, or make it an array instead of a list and use a parameter array:

[AttributeUsage(AttributeTargets.Method)]
public class FooAttribute : Attribute
{
    public FooAttribute(params string[] values)
    {
        ...
    }
}

[Foo("a", "b")]
static void SomeMethod()
{
}

Answer 2

You can't use List<T>.

Attributes have restrictions on parameters and property types, because they have to be available at compile-time. Using attributes in C#

Use an array instead:

//constructor
public CustomAuthorize(string[] _multipleProgramID) 
{
    ...
}

// usage
[CustomAuthorize(new string[] { ProgramList.SURVEY_INPUT, ProgramList.SURVEY_OUTPUT })]

Answer 3

我试图做类似的事情，最终传递了一个逗号分隔的string并在属性构造函数中使用string.Spilt(',')将其转换为数组。

Answer 4

You just need to use "params" keyword in your custom attribute constructor and make your programList "enum"

[CustomAttribute(ProgramList.SURVEY_INPUT, ProgramList.SURVEY_OUTPUT)]
[HttpPost]
public ActionResult DeleteWaterQualityItems(string sourceID, string wqID) {
    // ..other code...
}

in you custom attribute class use this

public class CustomAuthorize : AuthorizeAttribute {

//Constructor
public CustomAuthorize (params ProgramList[] programListTypes) {

            multipleProgramID= programListTypes;
        }

private ProgramList[] multipleProgramID;

}

and you enum class

public enum ProgramList : int
{
SURVEY_INPUT = 001;
SURVEY_OUTPUT =002;

}

Answer 5

One possible option:

   public class ConstraintExpectedValues : ConstraintAttribute
    {

        public ConstraintExpectedValues(object[] expectedValues)
        {
            this.ExpectedValues = expectedValues;
        }

        public object[] ExpectedValues { get; set; }
    }

Usage:

[ConstraintExpectedValues(new object[] {5,7,9})]