Wahr are Result Filters and How to use Result Filters in .Net?

 Result Filters are a type of filter in the .NET framework that can be applied to controller actions or globally to all controller actions in an ASP.NET MVC application. Result Filters provide a way to execute code before or after the execution of a result, or to modify the result of an action method.

Result Filters are implemented as attributes that can be applied to an action method, or to the entire controller class to apply to all action methods in that controller. Result Filters can be used to perform a wide range of tasks, including:

• Caching: Cache the result of a view or action.
• Content negotiation: Modify the result based on the client's Accept header.
• Response compression: Compress the response content to reduce bandwidth.
• Response formatting: Modify the format of the response content, such as JSON or XML.

Result Filters can be created by implementing the IResultFilter interface, which provides two methods: OnResultExecuting and OnResultExecuted. These methods are called before and after the execution of the result, respectively.

Here's an example of a Result Filter that compresses the response content using gzip:

csharp
public class GZipResultFilter : ActionFilterAttribute, IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext filterContext)
    {
        var request = filterContext.HttpContext.Request;
        var acceptEncoding = request.Headers["Accept-Encoding"];
        if (!string.IsNullOrEmpty(acceptEncoding) && acceptEncoding.Contains("gzip"))
        {
            var response = filterContext.HttpContext.Response;
            response.AppendHeader("Content-Encoding", "gzip");
            response.Filter = new GZipStream(response.Filter, CompressionMode.Compress);
        }
    }

    public void OnResultExecuted(ResultExecutedContext filterContext)
    {
        // Nothing to do here
    }
}

In this example, the GZipResultFilter class inherits from ActionFilterAttribute and implements the IResultFilter interface. The OnResultExecuting method checks if the client supports gzip encoding, and if so, it modifies the response headers and creates a new GZipStream that will compress the response content. The OnResultExecuted method is empty, as there is no additional processing needed after the result has been executed.

To use this Result Filter, you can apply the GZipResultFilter attribute to an action method or to the entire controller class, like this:

csharp
[GZipResultFilter]
public ActionResult MyAction()
{
    // Do some work...
    return View();
}

When this action method is executed, the GZipResultFilter will be applied and the response content will be compressed using gzip if the client supports it.