Directories:
- App_Data/: contain app related data files like .mdf files, LocalDB, XML file. IIS won't serve files from this directory
- App_Start/: contain files (classes) needed to be executed at app start time (mostly configuration files). e.g. of classes: BundleConfig, FilterConfig, RouteConfig, etc.
- Content/: store static files. e.g. imgs, CSS, icons
- Controllers/: contain all controllers classes
- fonts/: custom font files
- Models/: store class files of domain data. e.g. business logic
- Scripts/: contain JS files. e.g. jQuery, bootstrap
- Views/: store .cshtml files used to render HTML.
  - Each subdir in Views correspond to a controller
  - Also has a Shared folder for shared views. e.g. error, layout, etc.
Config files created by framework when creating project:
- Global.asax/ store code to run at app level (explained later)
- Packages.config: NuGet packages
- Web.config/: store application-level configurations

Controllers in ASP.NET MVC App

Summary of Controllers:

Parent class of Controller: A controller in MVC is a class that's inherited from System.Web.Mvc.Controller
Function of Controller: interact with Models and Views
Location of Controller classes: must be located in /Controller folder
What it has: A controller class contains a set of public methods which are called action methods. These action methods are used to handle incoming URL.
Naming pattern of Controller .cs files: In ASP.NET MVC, every controller class name must end with word "Controller". e.g. controller for the home page must be HomeController, controller for a student must be StudentController

What's a Controller in ASP.NET MVC?

A Controller = a class with public methods (aka action methods or simple actions). These public methods are used by MVC to handle incoming HTTP requests.

How to Create a Controller in MVC?

IDE provides GUI shortcut to create controller following Adding Controller to the Project

Location of Controllers:
- in ASP.NET MVC, controller classes are in /Controllers folder and inherit System.Web.Mvc.Controller, named as xxxController
URL mapping in ASP.NET MVC:
- http://localhost:xxxx/Home/Index map to class HomeController -> Index() method
- This mapping is defined in RegisterRouters() method of RouteConfig class in App_Start folder (for app initialization)
- Default route for HomeController (i.e. Home/Index page) shown below

routes.MapRoute(
    name: "Default", // Default Route
    url: "{controller}/{action}/{id}", // URL Pattern
    defaults: new {
      controller = "Home",  // Contoller for the mapped page
      action = "Index", // Action method within controller
      id = UrlParameter.Optional // id within page, currently it's optional
      }
);

Default Controller class is shown as below

namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        // GET: Home
        public ActionResult Index()
        {
            return View();
        }
    }
}

Which will create problem when running, as View() is not defined. So to fix the problem, we can just the public method to return string

e.g.

        public string Index()
        {
            return "Hello MVC5 Application";
        }

Also we can parse args to controller:

URL can parse args by /10?name=James from URL into controller method
method can use Request.QueryString to retrieve string parameter

Parse string parameter method 1:

public string Index(string id, string name)
{
    return "The value of  Id = " + id + " and Name = " + name;
}

Parse string paramter method 2:

public string Index(string id, string name)
{
    return "Id = " + id + " ,Name = " + Request.QueryString["name"];
}

To see them, enter URL http://localhost:xxxx/Home/Index/10?name=James

Views in ASP.NET MVC

What are Views in ASP.NET MVC?

Views in ASP.NET MVC = HTML templates embedded with Razor syntax. It generate/render HTML content to send to client

Where ASP.NET MVC View Files are Stored?

Views files in ASP.NET MVC have .cshtml extention. (Only when we use C#)
Within /Views folder, each controller has a controller-specific subdirectory to store controller-specific .cshtml views.
View file name and controller action name should be the same

e.g. Views Folder Structure

ASP.NET MVC app has HomeController & StudentController classes, where

HomeController has action methods AboutUs(),ContactUs() and Index()
StudentController has action methods Index(), Details(), Edit() and Delete()

Views are created in following structure

Understanding Views (Error)

If View is not created (correctly), following message will show

Understanding the error message: When Home Controller return a view from the index action method, MVC Framework perform following search:

Look for a file with name Index.aspx or Index.ascx in /Views//Home or /Views/Share directory
If not found, it search a view file Index.cshtml or Index.vbhtml (for VisualBasic) within /Views/Home or /Views/Shared directory

How to create/add Views in ASP.NET MVC Application?

In VS2019

right click method (e.g. Index()) -> Add View
Modify views by changing html content

Models in ASP.NET MVC

Summary of topic:

What are the Models in ASP.NET MVC?
How to create and user Models in MVC

What are the Models in ASP.NET MVC?

Models is used to manage domain data

contain classes that represent business data
contain classes with logic to manage business data

Location model:

(Good practice) within Models folder of MVC

How to create & user Models in MVC

Create Employee.cs in /Models, which has data structure that represent Employee
Create EmployeeBusinessLayer.cs in /Models, which contains business logic to manage employee data (e.g. CRUD operation)
Modify HomeController.cs to use these

e.g. Employee.cs

namespace FirstMVCDemo.Models
{
    public class Employee
    {
        public int EmployeeId { get; set; }
        public string Name { get; set; }
        public string Address { get; set; }
        public string City { get; set; }
        public string Gender { get; set; }
        public decimal Salary { get; set; }
    }
}

e.g. EmployeeBusinessLayer.cs

namespace FirstMVCDemo.Models
{
    public class EmployeeBusinessLayer
    {
        public Employee GetEmployeeDetails(int EmployeeId)
        {
            //Here we hardcoded the data
            //later we will discuss how to retrieve
            //the data from a database
            Employee employee = new Employee()
            {
                EmployeeId = EmployeeId,
                Name = "Pranaya",
                Gender = "Male",
                City = "Mumbai",
                Salary = 1000,
                Address = "Andheri"
            };
            return employee;
        }
    }
}

Next: learn how to pass data from controller (after extract data from Model) to view using ViewData

ViewData in ASP.NET MVC

Summary of topic:

What is ViewData in ASP.NET MVC?
How to Pass and Retrieve data From ViewData in ASP.NET MVC?
Example of ViewData in ASP.NET MVC.

In ASP.NET MVC app, we can pass model data from a controller to a view in many ways:

ViewBag (introduced here)
ViewData
TempData
Session or Application State varaible from traditional Web Forms

What is ViewData in ASP.NET MVC?

ViewData = a mechanism to pass data from a controller action method to a view (Uni-directional).

Internally It's a dictionary preoperty of ControllerBase class (it's the base class of Controller class)
ViewData is a Dictionary type (ViewDataDictionary actually), whereas ViewBag is of dynamic type
As a dictionary type, it contains key-value pairs where each key must be a string. e.g. ViewData["Name"]

using System.Web.Routing;

namespace System.Web.Mvc
{
    //
    // Summary:
    //     Represents the base class for all MVC controllers.
    public abstract class ControllerBase : IController
    {
        //
        // Summary:
        //     Initializes a new instance of the System.Web.Mvc.ControllerBase class.
        protected ControllerBase();

        public ControllerContext ControllerContext { get; set; }
        public TempDataDictionary TempData { get; set; }
        public bool ValidateRequest { get; set; }
        public IValueProvider ValueProvider { get; set; }
        //
        // Summary:
        //     Gets the dynamic view data dictionary.
        //
        // Returns:
        //     The dynamic view data dictionary.
        public dynamic ViewBag { get; }
        //
        // Summary:
        //     Gets or sets the dictionary for view data.
        //
        // Returns:
        //     The dictionary for the view data.
        public ViewDataDictionary ViewData { get; set; }
        protected virtual void Execute(RequestContext requestContext);
        protected abstract void ExecuteCore();
        protected virtual void Initialize(RequestContext requestContext);
    }
}

How to Pass and Retrieve data From ViewData in ASP.NET MVC?

i.e. "How to transfer data from controller to view using ViewData"

As data are stored as an object (like JSON object) in ViewData, so retrieving data from ViewData require type casting.

ViewData in MVC with String Type:
- Pass/Store data in Controller: ViewData["Header"] = "Employee Details
- Retreive data in View: @ViewData["Header"] (No type casting is required for string object)
ViewData in MVC with Complex Type:
- Pass/Store data in Controller: ViewData["Employee"] = employee
- Retreive data in View:

@{
    var employee = ViewData["Employee"] as FirstMVCDemo.Models.Employee;
}

Some Note about ViewData:

ViewData in MVC is resolved dynamically at runtime. Hence, no compileer-time error checking (e.g. miss-spell key names)

e.g. from tutorialsteacher

ViewData in Action method

public ActionResult Index()
{
    IList<Student> studentList = new List<Student>();
    studentList.Add(new Student(){ StudentName = "Bill" });
    studentList.Add(new Student(){ StudentName = "Steve" });
    studentList.Add(new Student(){ StudentName = "Ram" });

    ViewData["students"] = studentList;
  
    return View();
}

Access ViewData in Razor View

<ul>
@foreach (var std in ViewData["students"] as IList<Student>)
{
    <li>
        @std.StudentName
    </li>
}
</ul>

ViewBag in ASP.NET MVC

Topics:

What is ViewBag in ASP.NET MVC?
How to Pass and Retreive data from ViewBag in ASP.NET MVC?
Example of ViewBag in MVC
What are Difference and Similarities btw ViewData and ViewBag in ASP.NET MVC?

What is ViewBag in ASP.NET MVC?

As shown before, ViewBag is a dynamic property of Controller base class. It can transfer data from a controller action method to view

[Dynamic]
public dynamic ViewBag { get; }

How to Pass and Retrieve data From ViewBag in ASP.NET MVC?

ViewData in MVC with String Type:
- Pass/Store data in Controller: ViewData.Header = "Employee Details
- Retreive data in View: @ViewData.Header (No type casting is required for string object)
ViewData in MVC with Complex Type:
- Pass/Store data in Controller: ViewBag.Employee = employee;
- Retreive data in View
  - Advantage: No need to require typecasting while accessing data from a ViewBag

@{
    var employee = ViewData.Employee as FirstMVCDemo.Models.Employee;
}

Note: ViewBag is a dynamic property that also resolved at runtime, so no compile-time error checking.

Difference and Similarities

Similarity:

Both ViewData, ViewBag can be used to pass data from a Controller to a View.
Both are used to create loosely typed views
Both are resolved at runtime, no compiler-time error generated if mis-spell keynames or property name

Differences:

ViewData is a dictionary object, while ViewBag is a dynamic property
ViewData store data using key string, while ViewBag use dynamic properties
ViewData require typecasting for complex data, and also need check for null values to avoid exception, while ViewBag does not need

Best & Preferred way to pass data from Controller to View is Strongly Typed model, introduced next topic

Strongly Typed View in ASP.NET MVC

In MVC if pass data from a Controller to a View using ViewBag, TempData, or ViewData, the view becomes a loosely typed view.

Advantage of using strongly typed views:

Intellisense
Compile-time error checking

Creating Stronly Typed View in MVC

Q: How To create a strongly typed view in ASP.NET MVC app?
A: pass the model object as a parameter to View() extension method.

Controller base class provide 4 overloaded versions of View() extension method

protected internal ViewResult View(object model);
protected internal virtual ViewResult View (IView view, object model);
protected internal ViewResult View(string viewName, object model);
protected internal virtual ViewResult View(string viewName, string masterName, object model);

In Controller

Step 1. Pass object as parameter to View extension method

using FirstMVCDemo.Models;
using System.Web.Mvc;
namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            EmployeeBusinessLayer employeeBL = new EmployeeBusinessLayer();
            Employee employee = employeeBL.GetEmployeeDetails(101);
            ViewBag.Header = "Employee Details";
            
            return View(employee); // pass object as parameter
        }
    }
}

In View

Step 1. specify model type within the view by inserting @model FirstMVCDDemo.Models.Employee (lowercase m) before <!DOCTYPE html>

Step 2. Access model properties by using @Model (uppercase M), like <td>@Model.EmployeeId</td>

Advantages of using Strongly Typed View in ASP.NET MVC Application:

Advantage of strongly typed view in ASP.NET MVC app:

Strongly Typed View in ASP.NET MVC provides compile-time error checking as well as intelligence support.
Mis-spell property name will be spotted at compile time

ViewModel in ASP.NET MVC

A view may require multiple models, hence ViewModel is utilized.
A ViewModel in ASP.NET MVC app = a model which contains more than one model data required for a particular view.
This model is specific to a view only, hence called ViewModel

Understanding ViewModel in ASP.NET MVC

e.g. ViewModel design

Steps to create ASP.NET MVC:

Create models within /Models directory. e.g. Address.cs & Employee.cs
Create a viewmodel for containing models. e.g. EmployeeDetailsViewModel.cs that used to contain Employee and their address
Create a employee controller for using model & viewmodel, and pass ViewModel to view
Use ViewModel like strongly typed view in the view.

TempData in ASP.NET MVC

Why do we need TempData in ASP.NET MVC App?

Limits of ViewData, ViewBag, ViewModel:

ViewData & ViewBag: limited to onnly one HTTP request (e.g. if redirection occur, their value become null and lose data)
ViewModel: cannot used to pass data from one controller to another.

Where to use TempData:

Need to pass data from one HTTP Request to another.
Need to pass data from one controller to another

What is TempData in MVC?

TempData in ASP.NET MVC is the one of mechanism used to pass small amount of temporary data:

From 1 controller to its view (from A->controller to A->view)
From 1 action method to another action method within same controller (from A->controller->method1 to A->controller->method2)
From 1 controller action method to a action method in another controller (from A->controller->method to B->controller->method)

Find declaration of TempData from metadata

namespace System.Web.Mvc
{
    //
    // Summary:
    //     Represents the base class for all MVC controllers.
    public abstract class ControllerBase : IController
    {
        //
        // Summary:
        //     Initializes a new instance of the System.Web.Mvc.ControllerBase class.
        protected ControllerBase();
        
        // ...
        
        //
        // Summary:
        //     Gets or sets the dictionary for temporary data.
        //
        // Returns:
        //     The dictionary for temporary data.
        public TempDataDictionary TempData { get; set; }
        
        //...
    }
}

Find declaration of class TempDataDictionary in System.Web.Mvc.TempDataDictionary

public class TempDataDictionary : 
    IDictionary<string, object>,
    ICollection<KeyValuePair<string, object>>,
    IEnumerable<KeyValuePair<string, object>>,
    IEnumerable

As TempDataDictionary implement IDictionary interface, in MVC TempData is a dictionary object

It store data in key-value pairs:

Each key is a string
Each value is stored as object type

How to Pass and Retrieve data From TempData in ASP.NET MVC:

As value are stored as object, it must be casted when retreive

To Store data in TempData: TempData["YourDataKey"] = "SomeDataValue";
To retreive data from TempData: string strData = TempData["YourDataKey"].ToString(); type cast using string

e.g. pass and retreive data using TempData across action methods. However, data are not persistent

namespace FirstMVCDemo.Controllers
{
    public class EmployeeController : Controller
    {
        public ActionResult Method1()
        {
            TempData["Name"] = "Pranaya";
            TempData["Age"] = 30;
            return View();
        }

        public ActionResult Method2()
        {
            string Name;
            int Age;

            if (TempData.ContainsKey("Name"))
                Name = TempData["Name"].ToString();

            if (TempData.ContainsKey("Age"))
                Age = int.Parse(TempData["Age"].ToString());

            // do something with userName or userAge here 
            return View();
        }

        public ActionResult Method3()
        {
            string Name;
            int Age;

            if (TempData.ContainsKey("Name"))
                Name = TempData["Name"].ToString();

            if (TempData.ContainsKey("Age"))
                Age = int.Parse(TempData["Age"].ToString());

            // do something with userName or userAge here 
            return View();
        }
    }
}

Activate all action methods 1 by 1 via visiting URLs one after another:

1st Request: http://localhost:xxxxx/Employee/Method1
2nd Request: http://localhost:xxxxx/Employee/Method2
3rd Request: http://localhost:xxxxx/Employee/Method3

We cannot access TempData in method3, as TempData will be cleared out after 2nd request.

How to retain TempData values in the consecutive request?

Call TempData.Keep() after retreive data

namespace FirstMVCDemo.Controllers
{
    public class EmployeeController : Controller
    {
        public ActionResult Method1()
        {
            TempData["Name"] = "Pranaya";
            TempData["Age"] = 30;
            return View();
        }

        public ActionResult Method2()
        {
            string Name;
            int Age;

            if (TempData.ContainsKey("Name"))
                Name = TempData["Name"].ToString();

            if (TempData.ContainsKey("Age"))
                Age = int.Parse(TempData["Age"].ToString());

            TempData.Keep();

            // do something with userName or userAge here 
            return View();
        }

        public ActionResult Method3()
        {
            string Name;
            int Age;

            if (TempData.ContainsKey("Name"))
                Name = TempData["Name"].ToString();

            if (TempData.ContainsKey("Age"))
                Age = int.Parse(TempData["Age"].ToString());

            // do something with userName or userAge here 
            return View();
        }
    }
}