CODEWITHSUNDEEP
c#reflectiondelegatesattributes
millejos
millejos

Reputation: 321

Can I get a method attribute from a generic delegate?

I'm sure there's an answer already on the forum somewhere, but I haven't been able to find it so far. As per this example I am using anonymous methods in conjunction with a delegate in order to have different methods with the different parameters but the same return type all work as function parameters:

public delegate TestCaseResult Action();
...

[TestDescription("Test whether the target computer has teaming configured")]
public TestCaseResult TargetHasOneTeam()
{
  // do some logic here and return
  // TestCaseResult
}

[TestDescription("Test whether the target computer has the named team configured")]
public TestCaseResult TargetHasNamedTeam(string teamName)
{
  // do some logic here and return
  // TestCaseResult
}
...

public static void TestThat(TestCaseBase.Action action)
{
  TestCaseResult result = action.Invoke();

  // I want to get the value of the TestDescription attribute here
}
...

// usage
TestThat(() => TargetHasOneTeam());

TestThat(() => TargetHasNamedTeam("Adapter5"));

As you can see from the example, I'd really like to be able to get the TestDescriptionAttribute attribute from within the TestThat() function. I've already poked through the Action parameter which contains my method but haven't been able to "find" my TargetHasOneTeam() method.

Upvotes: 4

Views: 2181

Answers (4)

Val Bakhtin
Val Bakhtin

Reputation: 1464

If you change TestThat(() => TargetHasOneTeam()) (you wrapping your delegate into another action) to TestThat(TargetHasOneTeam) and change TestThat like this:

public static void TestThat(TestCaseBase.Action action)
{
  TestCaseResult result = action.Invoke();
  var attrs = action.GetInvocationList()[0].Method.GetCustomAttributes(true);

  // I want to get the value of the TestDescription attribute here
}

will give you what you need.

With expressions:

public static void TestThat(Expression<Func<TestResult>> action)
{
    var attrs = ((MethodCallExpression)action.Body).Method.GetCustomAttributes(true);

    var result = action.Compile()();
}

Upvotes: 4

Emmie Lewis-Briggman
Emmie Lewis-Briggman

Reputation: 855

See this example on MSDN. 

class TestAuthorAttribute
{
  static void Test()
  {
    PrintAuthorInfo(typeof(FirstClass));
    PrintAuthorInfo(typeof(SecondClass));
    PrintAuthorInfo(typeof(ThirdClass));
  }

  private static void PrintAuthorInfo(System.Type t)
 {
    System.Console.WriteLine("Author information for {0}", t);

    // Using reflection.
    System.Attribute[] attrs = System.Attribute.GetCustomAttributes(t);  // Reflection.

    // Displaying output.
    foreach (System.Attribute attr in attrs)
    {
        if (attr is Author)
        {
            Author a = (Author)attr;
            System.Console.WriteLine("   {0}, version {1:f}", a.GetName(), a.version);
        }
      }
  }

Upvotes: 0

Peter Ritchie
Peter Ritchie

Reputation: 35869

You can get the attribute of any member with Attribute.GetCustomAttribute. First check that the attribute is defined. For example:

public static void TestThat(TestCaseBase.Action action)
{
    TestCaseResult result = action.Invoke();
    if(System.Attribute.IsDefined(action.Method, typeof(TestDescriptionAttribute)))
    {
        var attribute = (TestDescriptionAttribute)System.Attribute.GetCustomAttribute(action.Method,
            typeof(TestDescriptionAttribute));
        Console.WriteLine(attribute.TestDescription);
    }
}

Upvotes: 1

JaredPar
JaredPar

Reputation: 755347

In this particular case it's essentially inaccessible. You are creating a lambda which executes the method in question. That lambda eventually results in a new method being generated which is eventually the argument of the Action delegate. That method has no relation to TargetHasOneTeam and is only apparently if you dig through the IL instructions in the body.

You could skip the lambda and do a method group conversion here. 

TestThat(TargetHasOneTeam);

Now TargetHasOneTeam is being directly assigned to the delegate instance and would be visible in the Delegate::MethodInfo property.

Note: In general though this is a bad idea for precisely the problem you're encountering. The attributes on the method shouldn't affect it's ability to satisfy the delegate instantiation. I would avoid this type of inspection if possible.

Upvotes: 4

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