Several frequently used patterns in ASP.NET Core involve HttpContext, configuration access, session handling, and custom action filters. This section outliens practical implementations.

Encapsulate a Global Static HttpContext Helper

A wrapper class provides convenient access to the current HttpContext:

// HttpContextAccessor is registered via services.AddHttpContextAccessor()
public static class AppHttpContext
{
    private static IHttpContextAccessor _accessor;
    
    public static void Configure(IHttpContextAccessor accessor)
    {
        _accessor = accessor;
    }

    public static string GetSessionString(string key) =>
        _accessor.HttpContext?.Session.GetString(key);
}

Reading JSON Configuration

Access nested settings using colon-separated keys:

// Assume IConfiguration is injected
string connectionString = _config.GetSection("Database:ConnectionString").Value;

Working with Session

Add the session middleware and install Microsoft.AspNetCore.Http package:

// In ConfigureServices:
services.AddSession();

// In Configure:
app.UseSession();

// Retrieve a value
string qrCode = AppHttpContext.GetSessionString("qrcode_key");

Custom Action Filter

Implement a filter by inheriting from Attribute and IActionFilter:

public class AuthorizationFilter : Attribute, IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        // Pre-execution logic
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        // Post-execution logic
    }
}

1. Getting the Current Controller Name

// Old MVC5 approach
// string controllerName = filterContext.ActionDescriptor.ActionName;

// .NET Core approach using ControllerType
string controllerName = context.Controller.GetType().Name;

2. Returning a View with Custom Data

var resultData = new ReturnMsg { Code = 500, Message = "Error" };
var viewData = new ViewDataDictionary<ReturnMsg>(
    ((Controller)context.Controller).ViewData, resultData);
context.Result = new ViewResult { ViewName = "error", ViewData = viewData };

3. Accessing Controller ViewBag

// Old style: filterContext.Controller.ViewBag.RightBtnView
if (context.Controller is Controller controller)
{
    controller.ViewBag.RightBtnView = btnView;
}

4. Retrieving Action Praameters

// Using ActionArguments dictionary (key-value pairs)
if (context.ActionArguments.TryGetValue("zbid", out object zbidObj))
{
    int zbid = Convert.ToInt32(zbidObj);
}

// Iterate parameter descriptors if only names are needed
foreach (var param in context.ActionDescriptor.Parameters)
{
    string paramName = param.Name;
}

5. Accessing Request Parameters List

// Form data keys
List<string> formKeys = context.HttpContext.Request.Form.Keys.ToList();

// Query string as array of key-value pairs
KeyValuePair<string, StringValues>[] queryPairs = context.HttpContext.Request.Query.ToArray();

5.1 Getting a Specific Parameter by Key

// From form collection
int zbid = Convert.ToInt32(
    context.HttpContext.Request.Form.FirstOrDefault(f => f.Key == "zbid").Value);

6. Retrieving the Referrer URL

string referer = context.HttpContext.Request.Headers["Referer"].FirstOrDefault();
// For MVC5: filterContext.HttpContext.Request.UrlReferrer.OriginalString;

7. Detecting an AJAX Request

public static bool IsAjaxRequest(this HttpRequest request)
{
    return request.Headers.TryGetValue("X-Requested-With", out var value) 
           && value == "XMLHttpRequest";
}

8. Resolving a Service from the Request Container

protected virtual T Resolve<T>() where T : class
{
    return this.HttpContext.RequestServices.GetService(typeof(T)) as T;
}