Today I am here to explain cookies in ASP.Net. You have seen “Remember Me” in every login portal or website. I will tell you how it works in this demo.

Cookies
It is a small text file stored in a client local machine or in the memory of a client browser session. It is used to state management. We can store a small piece of information in this file. It stores information in a plain text file.

How It Works

When the client sends a request to the server then the server sends response cookies with a session Id. If the cookies are saved the first time then the cookies are used for subsequent requests.

I am giving you a small demonstration. In this demonstration I will show you how to use use cookies and what “Remember Me” is.

When the user logs in with “Remember Me” selected then cookies play an important role. If Remember Me is selected then cookies will be created with the userid and an encrypted word. Cookies are easily readable for every user in the local machine. That’s why I use md5 to encryt my word for cookies.

Check cookies on Page_Load:
    HttpCookie _objCookie = Request.Cookies["Test"]; 
     
            if (_objCookie != null) 
            { 
                bool bCheck = IsValidAuthCookie(_objCookie, "encrypt"); 
                if (bCheck) 
                { 
                    Response.Redirect("WelcomePage.aspx?User=" + Convert.ToString(_objCookie.Value.ToString().Split('|')[0]) + ""); 
                } 
            } 

I check cookies on the login page load every time. If cookies exist then I redirect the welcome.aspx directly.
LoginButton_Click
    bool IsLogin = IsValidLogin(txtUserId.Text.Trim(), txtword.Text.Trim());   
    if (IsLogin)   
    {   
        if (chkRememberMe.Checked)   
        {   
            CreateAuthCookie(txtUserId.Text.Trim(), txtword.Text.Trim(), "encrypt");   
         }   
         Response.Redirect("WelcomePage.aspx?User=" + txtUserId.Text.Trim() + "");   
    }

If “Remember me” is checked then I create cookies with User Id and encrypted word.
Suppose you login with “Remember me” checked and close the application without LogOut. Now when you open again your login page it will redirect you to the welcome.aspx page automatically. And if you logout the application then your cookies will be removed. You will see this scenario on Gmail.com, Facebook.com and so on.

Create Hash word with Md5 encryption as in the following:
    public string CreateHash(string word, string salt) 
    { 
        // Get a byte array containing the combined word + salt. 
        string authDetails = word + salt; 
        byte[] authBytes = System.Text.Encoding.ASCII.GetBytes(authDetails); 
     
        // Use MD5 to compute the hash of the byte array, and return the hash as 
        // a Base64-encoded string. 
        var md5 = new System.Security.Cryptography.MD5CryptoServiceProvider(); 
        byte[] hashedBytes = md5.ComputeHash(authBytes); 
        string hash = Convert.ToBase64String(hashedBytes); 
     
        return hash; 
    } 

Advantages
Cookies do not require any server resources since they are stored on the client.
Cookies are easy to implement.

Disadvantages
Cookies can be disabled on user browsers
Cookies are transmitted for each HTTP request/response causing overhead on bandwidth
No security for sensitive data.

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I have listed down some of the assembly attributes.

    [assembly: AssemblyKeyFile(@"key.snk")] 
    [assembly: InternalsVisibleTo("System.Numerics, PublicKey=00000000000000000400000000000000", AllInternalsVisible=false)] 
    [assembly: Debuggable(DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints)] 
    [assembly: AssemblyDelaySign(true)] 
    [assembly: InternalsVisibleTo("System, PublicKey=00000000000000000400000000000000", AllInternalsVisible=false)] 
    [assembly: InternalsVisibleTo("System.Core, PublicKey=00000000000000000400000000000000", AllInternalsVisible=false)] 
    [assembly: AllowPartiallyTrustedCallers] 
    [assembly: NeutralResourcesLanguage("en-US")] 
    [assembly: RuntimeCompatibility(WrapNonExceptionThrows=true)] 
    [assembly: Guid("BED7F4EA-1A96-11d2-8F08-00A0C9A6186D")] 
    [assembly: ComCompatibleVersion(1, 0, 0xce4, 0)] 
    [assembly: TypeLibVersion(2, 4)] 
    [assembly: DefaultDependency(LoadHint.Always)] 
    [assembly: StringFreezing] 
    [assembly: ComVisible(false)] 
    [assembly: CLSCompliant(true)] 
    [assembly: CompilationRelaxations(8)] 
    [assembly: SecurityRules(SecurityRuleSet.Level2, SkipVerificationInFullTrust=true)] 
    [assembly: AssemblyTitle("sample.dll")] 
    [assembly: AssemblyDescription("sample.dll")] 
    [assembly: AssemblyDefaultAlias("sample.dll")] 
    [assembly: AssemblyCompany("Microsoft Corporation")] 
    [assembly: AssemblyProduct("Microsoft\x00ae .NET Framework")] 
    [assembly: AssemblyCopyright("\x00a9 Microsoft Corporation.  All rights reserved.")] 
    [assembly: AssemblyFileVersion("4.0.30319.225")] 
    [assembly: AssemblyInformationalVersion("4.0.30319.225")] 
    [assembly: SatelliteContractVersion("4.0.0.0")] 
    [assembly: AssemblyTargetedPatchBand("1.0.21-102")] 
    [assembly: SecurityPermission(SecurityAction.RequestMinimum, SkipVerification=true)] 

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In developing mobile web backends you might need users to broadcast messages such as push notifications to single or all  mobile subscribers from the cloud using services like Firebase Cloud Messaging (FCM).
 
In this article we will focus on sending push notifications from a .Net application using Firebase.Notification library. This library makes it very easy to send push notifications from Firebase using C#
 
To begin, download the library from Nuget:
    Install-Package Firebase.Notification -Version 1.0.0 

Using the library:
    using (var firebase = new Firebase()) 
    { 
        firebase.ServerKey = "{Your Server Key}"; 
        var id = "{Your Device Id}"; 
        firebase.PushNotifyAsync(id,"Hello","World").Wait(); 
        Console.ReadLine(); 
    }        

Error Handling and Debugging
Trace errors in your output window, all errors from this library will be captured under the category Firebase.Notification for easy debugging,

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An application is said to be multilingual if it can be deployed in many different languages. With .NET, all of the languages including Visual Basic, .NET, C#, and J# compile to a common Intermediate language (IL). This makes all languages interoperable. Microsoft has created Java bytecode, which is a low-level language with a simple syntax, which can be very quickly translated into native machine code.

CLR
.NET Framework is a multilingual application because of CLR.CLR is the key of .NET Framework. The code running under the control of the CLR is often termed as managed code.The main task of CLR is to convert compiled code into the native code. .NET Framework has one or more compilers; for e.g., VB .NET, C#, C++, JScript or any third party compiler such as COBOL.

Anyone of these compilers will convert your source code into Microsoft Intermediate Language (MSIL). The main reason for .NET to be multilingual is that you can compile your code from IL and this compiled code will be interoperable with the code that has been compiled to IL from another language.

It simply means that you can create pages in different languages (like C#, VB .NET, J# etc.) and once all of these pages are compiled they all can be used in a single application. Let us understand this point clearly with an example.

Let us consider a situation where a customer needs an application to be ready in 20 days. For completing the application in 20 days we want 30 developers who all know the specific language but we have 15 developers who know C# and 15 developers who know VB .NET. In this situation, if we don’t use .NET then we need to hire 15 more developers of C# or VB .NET which is a difficult and costly solution. Now, if we use .NET then we can use C# and VB .NET language in the same application. This is possible because once C# code is compiled from IL it becomes interoperable with VB .NET code which is compiled from IL.

Then JIT (Just In Time) of CLR converts this MSIL code into native code using metadata which is then executed by OS.

CLR stands for common language runtime. Common language runtime provides other services like memory management, thread management, remoting, and other security such as CTS and CLS. CLR is a layer between an operating system and .NET language, which uses CTS and CLS to create code.

CTS
CTS stands for the common type system. CTS defines rules that common language runtime follows when we are declaring, using and managing type. CTS deals with the data type. .NET supports many languages and every language has its own data type. One language cannot understand data types of another language. For example: When we are creating an application in C#, we have int and when we are creating an application in VB .NET, we have an integer. Here CTS comes into play --  after the compilation, CTS converts int and integer into the int32 structure.

CLS
CLS stands for common language specification. CLS is a subset of CTS and it declares all the rules and restrictions that all languages under .NET Framework must follow. The language which follows these rules is known as CLS compliant. For example, we can use multiple inheritances in c++ but when we use the same code in C# it creates a problem because C# does not support multiple inheritances. Therefore, CLS restricts multiple inheritances for all language. One other rule is that you cannot have a member with the same name and a different case.

In C# add() and Add() are different because it is case sensitive but a problem arises when we use this code in VB .NET because it is not case-sensitive and it considers add() and Add() as the same.

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Recently, I was working with a library which helps to generate barcode within images, the open source library is called ZXing (http://zxingnet.codeplex.com/). Its a free library with lots of great features and even supports QRCode generation. The only missing feature I came across was of writing a Barcode Text below the generated image. I reached out ZXing support team, here they replied to my thread.
http://zxingnet.codeplex.com/discussions/452290

Implementing such functionality in an html page was not that a big task.

Anyway here I came up with a solution. Hope this helps you..
<div style="border: 1px double black;width:50%;text-align:center;" id="PrintBarcode"> 
<div><asp:Image ID="imgBarcode" runat="server" /></div> 
<div style="margin-top:-10px;"><asp:Label ID="lblTexttoDisplay" runat="server"></asp:Label></div> 
</div><br /> 
<a ID="PrintMe" runat="server" Text="Print" onclick=""></a> 
<script type="text/javascript"> 
function PrintMe() 
{    
var popupWin = window.open('', '_blank', 'width=0,height=0,directories=0,fullscreen=0,location=0,menubar=0, 
 
                     resizable=0,scrollbars=0,status=0,titlebar=0,toolbar=0'); 
popupWin.document.open(); 
var divToPrint = document.getElementById('PrintBarcode'); 
popupWin.document.write('<html><body onload="window.print();this.close();"> 
 
          <div style="border: 0px double black;width:50%;text-align:center;">' + divToPrint.innerHTML + '</div></html>'); 
} 
</script> 

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In this article, I will be explaining how to create a simple Web Calculator using .NET Core.

What is ASP.NET Core and why do we use it?

• Easy to develop Web Pages as well as Web APIs.
• Integration of modern frameworks and development workflows.
• Easy to integrate with Azure.
• Natural dependency injection support.
• Large hosting variety, like on IIS, Apache, Docker, or self-host in your own process.
• A wide range of tools that simplifies web development.
• Multi-platform, so you may build and run on Windows, macOS, and Linux.
• Open-source and with a powerful community.

We are using a single controller with two Action Results - one for the first HttpGet and another to calculate the operation on the server side. Here is the code.
public class HomeController : Controller 
{ 
    [HttpGet] 
    public IActionResult Index() 
    { 
        return View(); 
    } 
 
    [HttpPost] 
    public IActionResult Index( Operation model ) 
    { 
        if ( model.OperationType == OperationType.Addition ) 
            model.Result = model.NumberA + model.NumberB; 
        return View( model ); 
    } 
} 

This is the View,
@model Operation 
<form asp-controller="Home" asp-action="Index" method="post" > 
    <div class="form-group"> 
        <div class="row"> 
            <label asp-for="NumberA" class="col-lg-2"></label> 
            <input type="number" asp-for="NumberA" class="col-lg-2" /> 
        </div> 
        <div class="row"> 
            <label asp-for="NumberB" class="col-lg-2"></label> 
            <input type="number" asp-for="NumberB" class="col-lg-2" /> 
        </div> 
        <div class="row"> 
            <label asp-for="OperationType" class="col-lg-2"></label> 
            <select asp-for="OperationType" class="col-lg-2" asp-items="Html.GetEnumSelectList<OperationType>()"> 
                <option selected="selected" value="">Select</option> 
            </select> 
        </div> 
        <div class="row"> 
            <label asp-for="Result" class="col-lg-2"></label> 
            <input type="number" disabled="disabled" class="col-lg-2" asp-for="Result" /> 
        </div> 
        <div class="row"> 
            <input type="submit" value="Submit" asp-action="Index" /> 
        </div> 
    </div> 
</form> 

View Result in the browser.

This is the model used in here.

public class Operation 
{ 
    [Display( Name = "First Number" )] 
    public double NumberA { get; set; } 
 
    [Display( Name = "Second Number" )] 
    public double NumberB { get; set; } 
 
    [Display( Name = "Result" )] 
    public double Result { get; set; } 
 
    [Display( Name = "Operation" )] 
    public OperationType OperationType { get; set; } 
} 

public enum OperationType 
{ 
    Addition, 
    Multiplication, 
    Division, 
    Subtraction 
} 

Right now, only addition is implemented.

You can implement multiplication, division, and subtraction as well. I will publish these methods in my next article.

Congratulations, you have successfully created your Web Calculator using .NET Core.

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In order to include an Area in an ASP.NET Core app, first we need to include a conventional route in the Startup.cs file (It's best to place it before any non-area route).

In Startup.cs, configure the method.
    app.UseMvc(routes =>  
    {  
        routes.MapRoute("areaRoute", "{area:exists}/{controller=Admin}/{action=Index}/{id?}");  
        routes.MapRoute(name: "default", template: "{controller=Home}/{action=Index}/{id?}");  
    });   

Then, make a folder named Areas in the app root and make another directory named Admin inside the former. Inside the admin folder, create the following folders (ViewComponent is optional).

Now, we will create a Controller inside the Controllers folder named AdminController.
Now, in order for that to work, you'll need to create Views for all actions that return one. The hierarchy for Views is just like what you have in a non-area Views folder.

Now, you should be good to go!

Question - What if I want to have another Controller inside my Area?

Answer -
Just add another Controller beside AdminController and make sure the routes are like the following,
    [Area("Admin")]  
    [Route("admin/[controller]")]  
    public class ProductsController: Controller {  
        publicProductsController() {  
                //  
            }  
            [Route("{page:int?}")]  
        publicIActionResult Index() {  
            returnView();  
        }  
    }   

The important part is [Route("admin/[controller]")]. With that, you can keep the style of routing to admin /controller/ action/.

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