这个概念用于MVC http://en.wikipedia.org/wiki/ASP.NET_MVC_Framework网络应用程序。
The .NET框架4.x提供了几个触发操作的属性，例如：ExceptionFilterAttribute（处理异常），AuthorizeAttribute（处理授权）。两者都定义在System.Web.Http.Filters.
例如，您可以定义自己的授权属性，如下所示：
public class myAuthorizationAttribute : AuthorizeAttribute
{
protected override bool IsAuthorized(HttpActionContext actionContext)
{
// do any stuff here
// it will be invoked when the decorated method is called
if (CheckAuthorization(actionContext))
return true; // authorized
else
return false; // not authorized
}
}
然后，在你的控制器类，您装饰应该使用您的授权的方法，如下所示：
[myAuthorization]
public HttpResponseMessage Post(string id)
{
// ... your code goes here
response = new HttpResponseMessage(HttpStatusCode.OK); // return OK status
return response;
}
每当Post方法被调用时，它会调用IsAuthorized里面的方法myAuthorization属性before里面的代码Post方法被执行。
如果你回来false in the IsAuthorized方法，您发出信号表示未授予授权并且该方法的执行Post aborts.
为了理解它是如何工作的，让我们看一个不同的例子：ExceptionFilter，它允许使用属性过滤异常，其用法与上面所示的类似AuthorizeAttribute（您可以找到有关其用法的更详细说明here https://learn.microsoft.com/en-us/aspnet/web-api/overview/error-handling/exception-handling).
要使用它，请导出DivideByZeroExceptionFilter类来自ExceptionFilterAttribute如图所示here http://blog.karbyn.com/articles/handling-errors-in-web-api-using-exception-filters-and-exception-handlers/，并重写该方法OnException:
public class DivideByZeroExceptionFilter : ExceptionFilterAttribute
{
public override void OnException(HttpActionExecutedContext actionExecutedContext)
{
if (actionExecutedContext.Exception is DivideByZeroException)
{
actionExecutedContext.Response = new HttpResponseMessage() {
Content = new StringContent("A DIV error occured within the application.",
System.Text.Encoding.UTF8, "text/plain"),
StatusCode = System.Net.HttpStatusCode.InternalServerError
};
}
}
}
然后使用以下演示代码来触发它：
[DivideByZeroExceptionFilter]
public void Delete(int id)
{
// Just for demonstration purpose, it
// causes the DivideByZeroExceptionFilter attribute to be triggered:
throw new DivideByZeroException();
// (normally, you would have some code here that might throw
// this exception if something goes wrong, and you want to make
// sure it aborts properly in this case)
}
现在我们知道了它是如何使用的，我们主要对实现感兴趣。以下代码来自 .NET Framework。它使用接口IExceptionFilter内部作为合同：
namespace System.Web.Http.Filters
{
public interface IExceptionFilter : IFilter
{
// Executes an asynchronous exception filter.
// Returns: An asynchronous exception filter.
Task ExecuteExceptionFilterAsync(
HttpActionExecutedContext actionExecutedContext,
CancellationToken cancellationToken);
}
}
The ExceptionFilterAttribute其本身定义如下：
namespace System.Web.Http.Filters
{
// Represents the attributes for the exception filter.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method,
Inherited = true, AllowMultiple = true)]
public abstract class ExceptionFilterAttribute : FilterAttribute,
IExceptionFilter, IFilter
{
// Raises the exception event.
// actionExecutedContext: The context for the action.
public virtual void OnException(
HttpActionExecutedContext actionExecutedContext)
{
}
// Asynchronously executes the exception filter.
// Returns: The result of the execution.
Task IExceptionFilter.ExecuteExceptionFilterAsync(
HttpActionExecutedContext actionExecutedContext,
CancellationToken cancellationToken)
{
if (actionExecutedContext == null)
{
throw Error.ArgumentNull("actionExecutedContext");
}
this.OnException(actionExecutedContext);
return TaskHelpers.Completed();
}
}
}
Inside ExecuteExceptionFilterAsync， 方法OnException叫做。由于您已如之前所示覆盖了它，因此现在可以通过您自己的代码来处理该错误。
正如 OwenP 的回答中提到的，还有一种商业产品可用，后锐利 http://www.postsharp.net/，这可以让您轻松做到这一点。Here http://doc.postsharp.net/method-interception#intercepting-method是一个如何使用 PostSharp 做到这一点的示例。请注意，有一个 Express 版本可供您免费使用，甚至可以用于商业项目。
PostSharp 示例（请参阅上面的链接以获取完整说明）：
public class CustomerService
{
[RetryOnException(MaxRetries = 5)]
public void Save(Customer customer)
{
// Database or web-service call.
}
}
这里该属性指定Save如果发生异常，该方法最多被调用 5 次。以下代码定义了此自定义属性：
[PSerializable]
public class RetryOnExceptionAttribute : MethodInterceptionAspect
{
public RetryOnExceptionAttribute()
{
this.MaxRetries = 3;
}
public int MaxRetries { get; set; }
public override void OnInvoke(MethodInterceptionArgs args)
{
int retriesCounter = 0;
while (true)
{
try
{
args.Proceed();
return;
}
catch (Exception e)
{
retriesCounter++;
if (retriesCounter > this.MaxRetries) throw;
Console.WriteLine(
"Exception during attempt {0} of calling method {1}.{2}: {3}",
retriesCounter, args.Method.DeclaringType, args.Method.Name, e.Message);
}
}
}
}
