CODEWITHSUNDEEP
c#attributes
RCPT
RCPT

Reputation: 323

Access to the value of a Custom Attribute

I've got this custom attribute:

[AttributeUsage(AttributeTargets.Method, AllowMultiple=false, Inherited = true)]
class MethodTestingAttibute : Attribute
{   
    public string Value{ get; private set; }
    public MethodTestingAttibute (string value)
    {
        this.Value= value;

    }
}

To be used like this:

[MethodTestingAttibute("2")]
public int m1() {return 3; }

And my difficulty is to take the value of "2" of MethodTestingAttibute

object result = method.Invoke(obj, new Type[] {}); // here i get the return

Now I want to compare this result to the value of MethodTestingAttibute. How can I do that? I'm trying to go up to this road but without success: 

method.GetCustomAttributes(typeof(MethodTestAttibute), true)[0]...

What is the proper way to get access to the field of the custom attribute?

Upvotes: 30

Views: 58608

Answers (6)

Joaquinglezsantos
Joaquinglezsantos

Reputation: 1630

With my custom attribute:

[AttributeUsage(AttributeTargets.Method)]
public class AttributeCustom : Attribute
{
    public string MyPropertyAttribute { get; private set; }

    public AttributeCustom(string myproperty)
    {
        this.MyPropertyAttribute = myproperty;
    }
}

I create a method for to get attribute with his values:

public static AttributeCustom GetAttributeCustom<T>(string method) where T : class
{
    try
    {
        return ((AttributeCustom)typeof(T).GetMethod(method).GetCustomAttributes(typeof(AttributeCustom), false).FirstOrDefault());
    }
    catch(SystemException)
    {
        return null;
    }
}

With a example class (must be not static because T is generic)

public class MyClass
{
    [AttributeCustom("value test attribute")])
    public void MyMethod() 
    {
        //...
    }
}

Usage:

var customAttribute = GetAttributeCustom<MyClass>("MyMethod");
if (customAttribute != null)
{
    Console.WriteLine(customAttribute.MyPropertyAttribute);
}

Upvotes: 5

Stefan Steiger
Stefan Steiger

Reputation: 82326

Necromancing.
For those that still have to maintain .NET 2.0, or those that want to do it without LINQ:

public static object GetAttribute(System.Reflection.MemberInfo mi, System.Type t)
{
    object[] objs = mi.GetCustomAttributes(t, true);

    if (objs == null || objs.Length < 1)
        return null;

    return objs[0];
}



public static T GetAttribute<T>(System.Reflection.MemberInfo mi)
{
    return (T)GetAttribute(mi, typeof(T));
}


public delegate TResult GetValue_t<in T, out TResult>(T arg1);

public static TValue GetAttributValue<TAttribute, TValue>(System.Reflection.MemberInfo mi, GetValue_t<TAttribute, TValue> value) where TAttribute : System.Attribute
{
    TAttribute[] objAtts = (TAttribute[])mi.GetCustomAttributes(typeof(TAttribute), true);
    TAttribute att = (objAtts == null || objAtts.Length < 1) ? default(TAttribute) : objAtts[0];
    // TAttribute att = (TAttribute)GetAttribute(mi, typeof(TAttribute));

    if (att != null)
    {
        return value(att);
    }
    return default(TValue);
}

Example usage:

System.Reflection.FieldInfo fi = t.GetField("PrintBackground");
wkHtmlOptionNameAttribute att = GetAttribute<wkHtmlOptionNameAttribute>(fi);
string name = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, delegate(wkHtmlOptionNameAttribute a){ return a.Name;});

or in your case simply 

MethodInfo mi = typeof(Vehicles).GetMethod("m1");
string aValue = GetAttributValue<MethodTestingAttibute, string>(mi, a => a.Value);

Upvotes: 1

Igby Largeman
Igby Largeman

Reputation: 16747

To get the value of an attribute property, just cast the object returned by GetCustomAttributes():

{
    string val;
    object[] atts = method.GetCustomAttributes(typeof(MethodTestAttibute), true);
    if (atts.Length > 0)
       val = (atts[0] as MethodTestingAttibute).Value;
}

Upvotes: 1

agent-j
agent-j

Reputation: 27943

var attribute =
   (MethodTestingAttibute)
   typeof (Vehicles)
      .GetMethod("m1")
      .GetCustomAttributes(typeof (MethodTestingAttibute), false).First();
Console.WriteLine(attribute.Value);

Upvotes: 35

Leonard Br&#252;nings
Leonard Br&#252;nings

Reputation: 13272

Check the code here http://msdn.microsoft.com/en-us/library/bfwhbey7.aspx

Excerpt:

        // Get the AClass type to access its metadata.
        Type clsType = typeof(AClass);
        // Get the type information for Win32CallMethod.
        MethodInfo mInfo = clsType.GetMethod("Win32CallMethod");
        if (mInfo != null)
        {
            // Iterate through all the attributes of the method.
            foreach(Attribute attr in
                Attribute.GetCustomAttributes(mInfo)) {
                // Check for the Obsolete attribute.
                if (attr.GetType() == typeof(ObsoleteAttribute))
                {
                    Console.WriteLine("Method {0} is obsolete. " +
                        "The message is:",
                        mInfo.Name);
                    Console.WriteLine("  \"{0}\"",
                        ((ObsoleteAttribute)attr).Message);
                }

                // Check for the Unmanaged attribute.
                else if (attr.GetType() == typeof(UnmanagedAttribute))
                {
                    Console.WriteLine(
                        "This method calls unmanaged code.");
                    Console.WriteLine(
                        String.Format("The Unmanaged attribute type is {0}.",
                                      ((UnmanagedAttribute)attr).Win32Type));
                    AClass myCls = new AClass();
                    myCls.Win32CallMethod();
                }
            }
        }

Upvotes: 0

dtb
dtb

Reputation: 217391

Cast the object to MethodTestingAttibute:

object actual = method.Invoke(obj, null);

MethodTestingAttibute attribute = (MethodTestingAttibute)method.GetCustomAttributes(typeof(MethodTestAttribute), true)[0];
string expected = attribute.Value;

bool areEqual = string.Equals(expected, actual != null ? actual.ToString() : null, StringComparison.Ordinal);

Upvotes: 1

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