从MVC中的Controller方法获取Attribute标签？

Question

I'm trying to get the Attribute tag from an API Controller so that I can see what HTTP verb it allows at runtime. From the sample code below, I want to be able to get the [HttpGet] tag.

[HttpGet]
public void MyResource()
{
    // Controller logic
}

I am currently using System.Reflection to gather other information about my API while it is running, but so far I have been unable to retrieve the [HttpGet tag and other Http verb tags. I've tried each of the solutions below with no luck:

public void GetControllerMethodHttpAttribute()
{
    MethodInfo controllerMethod = typeof(TestController).GetMethods().First();

    // Solution 1
    var attrs = controllerMethod.Attributes;

    // Solution 2
    var httpAttr = Attribute.GetCustomAttributes(typeof(HttpGetAttribute));

    // Solution 3
    var httpAttr2 = Attribute.GetCustomAttribute(controllerMethod, typeof(HttpGetAttribute));

    // Solution 4
    var httpAttr3 = Attribute.IsDefined(controllerMethod, typeof(HttpGetAttribute));
}

All of the previous questions that I've researched about this topic only related to Custom Attribute tags and pulling values out of those, but I couldn't find any information about getting the framework-included Attribute tags .

Does anyone know how I can get the [HttpGet] Attribute tag?

Thanks!

Answer 1

The proposed solutions 3 and 4 work.

You must look out that you are referencing the correct HttpGetAttribute . There is one in System.Web.Http.HttpGetAttribute and there is one in System.Web.Mvc.HttpGetAttribute .

The following code lists the public methods of the ValuesController API controller with the information on whether they have HttpGet or HttpPost attributes.

var methods = typeof(ValuesController).GetMethods();
string infoString = "";

foreach(var method in methods)
{
    // Only public methods that are not constructors
    if(!method.IsConstructor && method.IsPublic)
    {
        // Don't include inherited methods
        if(method.DeclaringType == typeof(ValuesController))
        {

            infoString += method.Name;

            if(Attribute.IsDefined(method, typeof(System.Web.Http.HttpGetAttribute)))
            {
                infoString += " GET ";
            }
            if(Attribute.IsDefined(method, typeof(System.Web.Http.HttpPostAttribute)))
            {
                infoString += " POST ";
            }


            infoString += Environment.NewLine;
        }
    }
}

You need to exchange System.Web.Http. with System.Web.Mvc. when the controller is an MVC controller instead of an API controller.

Answer 2

This is how I ended up doing it:

public static IEnumerable<Attribute> GetSupportedVerbsForAction<T>(
    Expression<Func<T, IActionResult>> expression)
    where T : Controller
{
    //only consider a list of attributes
    var typesToCheck = new[] { typeof(HttpGetAttribute), typeof(HttpPostAttribute),
        typeof(HttpPutAttribute), typeof(HttpDeleteAttribute), typeof(HttpPatchAttribute)};

    var method = ((MethodCallExpression)expression.Body).Method;

    var matchingAttributes = typesToCheck
        .Where(x => method.IsDefined(x))
        .ToList();

    //if the method doesn't have any of the attributes we're looking for,
    //assume that it does all verbs
    if (!matchingAttributes.Any())
        foreach(var verb in typesToCheck)
            yield return verb;

    //else, return all the attributes we did find
    foreach (var foundAttr in matchingAttributes)
    {
        yield return method.GetCustomAttribute(foundAttr);
    }
}

Say you have the following Controller and Actions:

public class HomeController : Controller
{
    // implicit get
    public IActionResult Index() => View();

    // explicit get
    [HttpGet]
    public IActionResult GetAction() => View();

    // extra info
    [HttpPost(Name = "some name", Order = 5)]
    public IActionResult PostAction() => View();

    [HttpPut]
    [HttpDelete]
    [HttpPatch("my template", Name = "patch name", Order = 333)]
    public IActionResult MultiAction() => View();
}

You can call them like this:

var indexVerbs = GetSupportedVerbsForAction<HomeController>(x => x.Index()).ToList();
var getVerbs = GetSupportedVerbsForAction<HomeController>(x => x.GetAction()).ToList();
var postVerbs = GetSupportedVerbsForAction<HomeController>(x => x.PostAction()).ToList();
var multiVerbs = GetSupportedVerbsForAction<HomeController>(x => x.MultiAction()).ToList();

This will return the full attribute that you've set in case you've added any custom data.

Two things to note:

1. You'll need to supply parameters to the function call. They don't need to be valid as the method itself won't be called, but I couldn't figure out how to allow you to do GetSupportedVerbsForAction<HomeController>(x => x.Index) .
2. The method will pass back a list of Attribute , so use the is keyword to figure out if it's the type you want.