C# 0 The Complete Reference

RemarkAttribute

. The 

Remark

 property 

cannot

 be 

used as a named parameter because it is read-only. Remember that only public, read-write 

fields and properties can be used as named parameters.

A public, read-write property can be used as a named parameter in the same way as 

a field. For example, here an auto-implemented 

int

 property called 

Priority

 is added to 

RemarkAttribute

:

// Use a property as a named attribute parameter.

using System;

using System.Reflection;

[AttributeUsage(AttributeTargets.All)]

public class RemarkAttribute : Attribute {

  string pri_remark; // underlies Remark property

  public string Supplement; // this is a named parameter

  public RemarkAttribute(string comment) {

    pri_remark = comment;

    Supplement = "None";

    Priority = 1;

  }

  public string Remark {

    get {

      return pri_remark;

    }

  }

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  // Use a property as a named parameter.

  public int Priority { get; set; }

}

[RemarkAttribute("This class uses an attribute.",

                 Supplement = "This is additional info.",

                 Priority = 10)]

class UseAttrib {

  // ...

}

class NamedParamDemo {

  static void Main() {

    Type t = typeof(UseAttrib);

    Console.Write("Attributes in " + t.Name + ": ");

    object[] attribs = t.GetCustomAttributes(false);

    foreach(object o in attribs) {

      Console.WriteLine(o);

    }

    // Retrieve the RemarkAttribute.

    Type tRemAtt = typeof(RemarkAttribute);

    RemarkAttribute ra = (RemarkAttribute)

          Attribute.GetCustomAttribute(t, tRemAtt);

    Console.Write("Remark: ");

    Console.WriteLine(ra.Remark);

    Console.Write("Supplement: ");

    Console.WriteLine(ra.Supplement);

    Console.WriteLine("Priority: " + ra.Priority);

  }

}

The output is shown here:

Attributes in UseAttrib: RemarkAttribute

Remark: This class uses an attribute.

Supplement: This is additional info.

Priority: 10

There is one point of interest in the program. Notice the attribute specified before 

UseAttrib

 that is shown here:

[RemarkAttribute("This class uses an attribute.",

                 Supplement = "This is additional info.",

                 Priority = 10)]

The named attributes 

Supplement

 and 

Priority

 are 

not

 in any special order. These two 

assignments can be reversed without any change to the attribute.

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