ASP.NET Core - MVC - Bootstrap - Responsive Web Programming - Lecture 4: Partial Views, Components

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In Lecture 4:
* What are partial views in ASP.NET MVC
* How to add and call partial views with default conventional path or with full path
* How to pass data into partial views
* How to access parent view's Model or ViewData in the called partial view
* How to use "is" and "as" keywords to write conditional and intellisense supporting code
* How to access and set elements of ViewData
* What is ViewComponent and how to use it
* How to reference Jquery and do async ajax call with Jquery $.get method

Enhancing Web Development with Partial Views, View Components, and More in ASP.NET MVC

Introduction

ASP.NET MVC is a powerful and flexible web development framework designed to create modern web applications. One of its many strengths lies in the ability to create reusable and modular components that can be easily integrated into different parts of an application. In this article, we will explore several topics that will help you understand and effectively use ASP.NET MVC to build robust and maintainable applications. These topics include partial views, passing data to partial views, using "is" and "as" keywords, accessing and setting elements of ViewData, ViewComponents, and performing async AJAX calls with jQuery.

Partial Views in ASP.NET MVC
Partial views are a feature in ASP.NET MVC that allows developers to create reusable view components that can be embedded in multiple views. This helps maintain a clean and organized codebase, as well as promote reusability and maintainability. Partial views are like regular views but are designed to render a specific part of the page, such as a header, footer, or a reusable widget.

Adding and Calling Partial Views
To create a partial view, add a new view file with the desired name and prefix it with an underscore (e.g., _PartialViewName.cshtml). The underscore indicates that the view is a partial view and should not be treated as a standalone view.

You can render a partial view using the Html.Partial or Html.RenderPartial methods. To call a partial view with a default conventional path, use the following syntax:

@Html.Partial("_PartialViewName")
If you want to use a full path, provide the path relative to the application's Views folder:

@Html.Partial("~/Views/Shared/_PartialViewName.cshtml")
Passing Data into Partial Views
To pass data from the parent view to a partial view, you can use the second parameter of the Html.Partial or Html.RenderPartial method. You can pass a model, a ViewDataDictionary, or an anonymous object:

@Html.Partial("_PartialViewName", Model)
Accessing Parent View's Model or ViewData in the Called Partial View
Inside the partial view, you can access the parent view's Model or ViewData using the Model and ViewData properties, respectively. For example, to access a property from the parent view's model, use the following syntax:

@Model.PropertyName
Using "is" and "as" Keywords for Conditional and Intellisense-Supporting Code
The "is" and "as" keywords in C# can be used to perform type checking and typecasting, respectively. The "is" keyword checks if an object is of a specific type, while the "as" keyword attempts to cast an object to a specific type without throwing an exception if the cast is invalid. These keywords can be useful when writing conditional code and providing Intellisense support.

For example, you can use the "is" keyword to check if a given object is of a specific type:

if (Model is CustomModel)
{
// Do something with CustomModel
}
To cast an object to a specific type using the "as" keyword:

CustomModel customModel = Model as CustomModel;
if (customModel != null)
{
// Do something with customModel
}
Accessing and Setting Elements of ViewData
ViewData is a dictionary that allows you to store and retrieve data in your views. To set a value in ViewData, use the following syntax in your controller action:

ViewData["Key"] = "Value";

ViewComponent and Its Usage
ViewComponents are another way to create reusable components in ASP.NET MVC. They are more powerful than partial views as they can have their own logic, accept parameters, and execute asynchronously. ViewComponents are useful for rendering complex components that require more processing than a simple partial view can provide.