Asp.net MVC 应用程序中经常使用ajax操作，一般都是一些action。我们来实现个特性标记当前某个action只支持处理ajax的http请求。 下面直接看代码 

/// <summary>
/// AjaxOnlyAttribute
/// </summary>
public class AjaxOnlyAttribute : ActionFilterAttribute
{
    /// <summary>
    /// Called by the ASP.NET MVC framework before the action method executes.
    /// </summary>
    /// <param name="filterContext">The filter context.</param>
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (!filterContext.HttpContext.Request.IsAjaxRequest())
        {
            filterContext.Result = new HttpNotFoundResult();
        }
        base.OnActionExecuting(filterContext);
    }
}

这里让它返回一个特别的HttpNotFoundResult, 以确保代码可读性:

/// <summary>
/// HttpNotFoundResult
/// </summary>
public class HttpNotFoundResult : ActionResult
{
    /// <summary>
    /// Enables processing of the result of an action method by a custom type that inherits from the <see cref="T:System.Web.Mvc.ActionResult"/> class.
    /// </summary>
    /// <param name="context">The context in which the result is executed. The context information includes the controller, HTTP content, request context, and route data.</param>
    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("Context");
        }
        context.HttpContext.Response.StatusCode = 401;
    }
}

在Action标记像这样:

[AjaxOnly]
public ActionResult LogOff()
{
    FormsAuthentication.SignOut();

    return RedirectToAction("Index", "Home");
}

如何工作的看Unit Test，分别包括了Ajax请求与非Ajax请求的场景.

[TestMethod]
public void Test_AjaxOnlyAttributeWithAjaxRequest()
{
    //arrange
    var header = new System.Collections.Specialized.NameValueCollection();
    header.Add("X-Requested-With", "XMLHttpRequest");

    var mockRequest = new Mock<HttpRequestBase>();
    mockRequest.SetupGet(http => http.Headers).Returns(header);

    var mockFiltercontext = new Mock<ActionExecutingContext>();
    mockFiltercontext.SetupGet(fc => fc.HttpContext.Request).Returns(mockRequest.Object);

    //act
    var ajaxAttribute = new AjaxOnlyAttribute();
    var filterContext = mockFiltercontext.Object;
    ajaxAttribute.OnActionExecuting(filterContext);

    //verify
    mockRequest.VerifyAll();

    //assert
    Assert.IsTrue(filterContext.HttpContext.Request.IsAjaxRequest());
    var httpNotFoundResult = filterContext.Result as Mvc3App.Extention.Attribute.HttpNotFoundResult;
    Assert.IsNull(httpNotFoundResult);
}


[TestMethod]
public void Test_AjaxOnlyAttributeWithNonAjaxRequest()
{
    //arrange
    var header = new System.Collections.Specialized.NameValueCollection();

    var mockRequest = new Mock<HttpRequestBase>();
    mockRequest.SetupGet(http => http.Headers).Returns(header);

    var mockFiltercontext = new Mock<ActionExecutingContext>();
    mockFiltercontext.SetupGet(fc => fc.HttpContext.Request).Returns(mockRequest.Object);

    var controllerContext = new ControllerContext
    {
        RequestContext = new RequestContext(new MockHttpContext(), new RouteData()),
        HttpContext = new MockHttpContext()
    };

    //act
    var ajaxAttribute = new AjaxOnlyAttribute();
    var filterContext = mockFiltercontext.Object;
    ajaxAttribute.OnActionExecuting(filterContext);

    //verify
    mockRequest.VerifyAll();

    //assert
    Assert.IsFalse(filterContext.HttpContext.Request.IsAjaxRequest());
    var httpNotFoundResult = filterContext.Result as Mvc3App.Extention.Attribute.HttpNotFoundResult;
    Assert.IsNotNull(httpNotFoundResult);
    httpNotFoundResult.ExecuteResult(controllerContext);
    Assert.AreEqual(controllerContext.HttpContext.Response.StatusCode, 401);
} 

MockHttpContext是一个用于Unit Test的类型，由于篇幅有限，这里不讲了。

希望对您Web开发有帮助。

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作者：Petter Liu
出处：http://www.cnblogs.com/wintersun/
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该文章也同时发布在我的独立博客中-Petter Liu Blog。