Sections in Layout View in ASP.NET Core MVC

Sections in Layout View in ASP.NET Core MVC

In this article, I am going to discuss the Sections in Layout View in ASP.NET Core MVC Application. Please read our previous article, where we discussed the Layout View in ASP.NET Core MVC Application. We will also work with the example we created in our previous article. As part of this article, we are going to discuss the following pointers.

  1. What are Sections in Layout View?
  2. Why Do We Need Sections in a Layout View?
  3. Understanding RenderSection and RenderSectionAsync Methods.
  4. How Do We Use the RenderSection Method in ASP.NET Core MVC?
  5. How to Provide Section Content in a Child View?
  6. Optional and Required Sections in ASP.NET Core MVC.
  7. How Do We Make the Layout Section Optional in ASP.NET Core MVC?
  8. RenderSection vs RenderSectionAsync Methods in ASP.NET Core MVC.
  9. Use Cases of Sections in Layout View in ASP.NET Core MVC.
  10. Need for Sections in a Layout View in ASP.NET Core MVC.
What are Sections in Layout View?

In ASP.NET Core MVC, the layout view is a shared template that can be used by multiple views to provide a consistent look and feel across the application. It helps in reducing the redundancy of common content like headers, footers, navigation menus, and so on. The layout view contains placeholders for the content that changes from one view to another, usually defined as sections. 

So, Sections in ASP.NET Core MVC layout views provide a way to define content blocks that child views can fill. They allow you to define placeholders in the layout view for specific content that varies from page to page. This mechanism is helpful for creating flexible and customizable layouts where different views can inject their own content into specific sections of the layout.

In ASP.NET Core MVC, the layout view contains one or more sections. The Sections in a layout view are used to organize where certain page elements should be placed. The sections in a layout view can be optional or mandatory. If this is unclear now, don’t worry; we will understand this with examples and see when it is mandatory and optional.

Why Do We Need Sections in a Layout View?

In order to understand the Need for Sections in a Layout View, let us first create a custom javascript file. First, create a folder at the root level of the application with the name wwwroot if not already there. As we are creating the project using Model-View-Controller, the wwwroot folder should be there.

In general, all the static files of our ASP.NET Core MVC Application need to be placed within this wwwroot folder. Once you have created the “wwwroot” folder, within wwwroot folder, create a subfolder within this with the name “js” if not already there, and then add a javascript file with the name “CustomJavascript.js” within the js folder.

To do so, right-click on the js folder and select Add => New Item from the context menu, which will open the New Item window. Here, search javascript, select Javascript File, give the file name CustomJavascript.js, and finally click the Add button, as shown in the image below.

Adding JavaScript File in ASP.NET Core MVC Application

Once you add the CustomJavascript.js file, your wwwroot folder should look as shown in the image below.

Sections in Layout View in ASP.NET Core MVC

Situation 1:

If we have a custom javascript file (i.e., CustomJavascript.js) and all the views of our application require that file, then we need to place that file in the Layout View of our application. Let us add that CustomJavascript.js file within our _Layout.cshtml file. So, modify the _Layout.cshtml file as follows.

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
</head>
<body>
    <table border="1" style="width:800px; font-family:Arial">

        <tr>
            <td colspan="2" style="text-align:center">
                <h3>Website Header</h3>
            </td>
        </tr>
        <tr>
            <td style="width:200px">
                <h3>Left Navigation Menus</h3>
            </td>
            <td style="width:600px">
                @RenderBody()
            </td>
        </tr>
        <tr>
            <td colspan="2" style="text-align:center; font-size:x-small">
                <h3>Website Footer</h3>
            </td>
        </tr>

    </table>
    <script src="~/js/CustomJavascript.js"></script>
</body>
</html>

Note: Putting all the script files before the closing body tag is always a good programming practice.

Situation 2:

Suppose you have a custom javascript file (i.e., CustomJavascript.js), and you want this file to be used in some specific views. Let’s assume you want this file in the Index view but not in the Details view of the Home Controller. In such scenarios, you can make use of the Section in ASP.NET Core MVC Application.

Understanding the RenderSection and RenderSectionAsync Method:

To use Section in ASP.NET Core MVC, we are provided with the RenderSection and RenderSectionAsync methods. Let us look at the signatures of the RenderSection and RenderSectionAsync methods, shown below.

Understanding the RenderSection Method in ASP.NET Core MVC

As you can see, two overloaded versions of the RenderSection Method exist. The same is the case for the RenderSectionAsync method. The first version of the Render section method takes a single parameter (i.e., name) that specifies the name of the section. The second overloaded version takes two parameters. The first parameter (name) specifies the name of the section, while the second parameter (required) specifies whether the section is required or optional.

  • name: The name of the section that you want to render.
  • required: A boolean value indicating whether the section is mandatory. If set to true, an exception is thrown if the section is not defined on the content page. If set to false, the layout will render without the section if it’s not present on the content page.

Note: The RenderSection method in ASP.NET Core MVC is utilized within layout pages to render sections from a content page. Sections provide a way to organize content in different blocks or areas on a web page, allowing for more flexible and maintainable page layouts. This method is especially useful in scenarios where you need to include optional or mandatory sections of content across various views, such as custom JavaScript, stylesheets, or other unique blocks of HTML.

How Do We Use the RenderSection Method in ASP.NET Core MVC?

From your layout view, you need to call the RenderSection() method at the location where you want the section content to be rendered. For example, we want the script file to be included before the closing </body> tag. So, here, we are calling the @RenderSection() method just before the closing </body> tag, as shown below.

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
</head>
<body>
    <table border="1" style="width:800px; font-family:Arial">

        <tr>
            <td colspan="2" style="text-align:center">
                <h3>Website Header</h3>
            </td>
        </tr>
        <tr>
            <td style="width:200px">
                <h3>Left Navigation Menus</h3>
            </td>
            <td style="width:600px">
                @RenderBody()
            </td>
        </tr>
        <tr>
            <td colspan="2" style="text-align:center; font-size:x-small">
                <h3>Website Footer</h3>
            </td>
        </tr>

    </table>
    @RenderSection("Scripts")
</body>
</html>

In the above code, we use the first overloaded version of the RenderSection method, which only takes the name parameter. In this case, the second parameter value will be true by default. That means mandatory.

How to Provide Section Content in a Child View?

In our layout view, we have created a section. Now, let us understand how to provide section content from the Child Views. Each and every view that wants to provide section content must include a section within the view. To do this, we need to use the @section directive to include the section and provide the content.

In our example, we want to provide the section content from the Index view. So, we need to modify the Index view as shown below. Here, you can see we are using @section Scripts {<script src=”~/js/CustomJavascript.js”></script>} as we are trying to include a javascript file. Here, we need to provide the section name as Scripts, and this is because, in the _Layout view, we have specified the section name as Scripts, i.e., @RenderSection(“Scripts”)

@{
    ViewBag.Title = "Home Page";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h1>Home Page</h1>
@section Scripts {
    <script src="~/js/CustomJavascript.js"></script>
}

Now run the application and navigate to the Home/Index URL, and you will see the out as expected, as shown in the below image.

How to Provide Section Content in a Child View?

But, when you navigate the Home/Details URL, you will get the following error page.

How to make the layout section optional in ASP.NET Core MVC

The reason for getting the above exception is the section is mandatory, and we have not specified the section content in the Details view. To verify this, go to the definition of the RenderSection(“Scripts”) method, which takes the string file name as a parameter, and you will see the following. As you can see, this method takes only the name parameter, and internally, it sets the required parameter value to true, making it mandatory to include the section in the child view. And in the Details view, we have not included any section.

RenderSection Method Signature in ASP.NET Core MVC

Optional and Required Sections in ASP.NET Core MVC

As mentioned, sections can be marked as required or optional in the layout:

  • Required Sections: If a section is marked as required in the layout and a view does not provide that section, an exception will be thrown. This is useful for parts of the layout that must always be customized by the view.
  • Optional Sections: If a section is marked as optional (required: false), the layout will render without the section content if the view does not define it. This is useful for parts of the page that are only occasionally customized.
How Do We Make the Layout Section Optional in ASP.NET Core MVC?

We can make a layout section optional in ASP.NET Core MVC in two ways. They are as follows:

Option 1: Use the RenderSection method, which takes two parameters. Set the second parameter (i.e., the required) to false.
@RenderSection(“Scripts”, required: false)
So, modify the _Layout.cshtml file as shown below to make the section optional.

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
</head>
<body>
    <table border="1" style="width:800px; font-family:Arial">

        <tr>
            <td colspan="2" style="text-align:center">
                <h3>Website Header</h3>
            </td>
        </tr>
        <tr>
            <td style="width:200px">
                <h3>Left Navigation Menus</h3>
            </td>
            <td style="width:600px">
                @RenderBody()
            </td>
        </tr>
        <tr>
            <td colspan="2" style="text-align:center; font-size:x-small">
                <h3>Website Footer</h3>
            </td>
        </tr>

    </table>
    @RenderSection("Scripts", false)
</body>
</html>

With the above changes in place, run the application and navigate to both URLs, and you should get the output as expected.

Option 2: Using the IsSectionDefined() method.

This method returns a value indicating whether the specified section is defined on the child view. If the section is defined in the child view, then the IsSectionDefined() method returns true, and in that case, the RenderSection method loads the content from the child view. If the method returns false, then the RenderSection method is not going to be executed and be ignored. So, modify the _Layout.cshtml file as shown below.

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>@ViewBag.Title</title>
</head>
<body>
    <table border="1" style="width:800px; font-family:Arial">

        <tr>
            <td colspan="2" style="text-align:center">
                <h3>Website Header</h3>
            </td>
        </tr>
        <tr>
            <td style="width:200px">
                <h3>Left Navigation Menus</h3>
            </td>
            <td style="width:600px">
                @RenderBody()
            </td>
        </tr>
        <tr>
            <td colspan="2" style="text-align:center; font-size:x-small">
                <h3>Website Footer</h3>
            </td>
        </tr>

    </table>
    @if (IsSectionDefined("Scripts"))
    {
        @RenderSection("Scripts")
    }
</body>
</html>

With the above changes in place, run the application and navigate to both URLs, and you should get the output as expected.

RenderSection vs RenderSectionAsync Methods in ASP.NET Core MVC

In ASP.NET Core MVC, RenderSection and RenderSectionAsync methods are used within layout pages to render sections from a view. These sections allow for a more modular and organized structure in your views, enabling the reuse of different parts of the HTML content across different views. The primary difference between the two methods lies in their mode of operation—synchronous versus asynchronous.

RenderSection

RenderSection is a synchronous method used in layout views to render a section defined in a view. A section is defined using the @section directive in the Razor view. The RenderSection method takes the name of the section as its first argument and an optional boolean parameter that indicates whether the section is required or not. Here’s a basic example of how RenderSection might be used in a layout view:

<!DOCTYPE html>
<html>
<head>
    <title>@ViewBag.Title</title>
</head>
<body>
    @RenderBody()

    @RenderSection("Scripts", required: false)
</body>
</html>

In this example, @RenderBody() renders the main content of the view, while @RenderSection(“Scripts”, required: false) attempts to render a section named “Scripts”. The required: false parameter indicates that the section is optional; if the section isn’t defined in a view using this layout, the layout will still be rendered without throwing an error.

RenderSectionAsync

RenderSectionAsync is the asynchronous counterpart to RenderSection. It operates similarly in that it is used to render sections defined in views, but it does so asynchronously. This can be useful when the content of the section involves I/O operations, such as database calls or reading from files, which can be performed asynchronously to improve the performance of your application. The use of RenderSectionAsync looks similar to RenderSection, but it requires the await keyword because it is an asynchronous method:

<!DOCTYPE html>
<html>
<head>
    <title>@ViewBag.Title</title>
</head>
<body>
    @RenderBody()

    @await RenderSectionAsync("Scripts", required: false)
</body>
</html>
Key Differences Between RenderSection and RenderSectionAsync Methods
  • Execution: RenderSection executes synchronously, while RenderSectionAsync executes asynchronously.
  • Use Case: RenderSectionAsync is preferred when the section content involves asynchronous operations. Using RenderSectionAsync can help in not blocking the web server thread, potentially improving the overall performance of the application.
Best Practices
  • Use RenderSectionAsync when the content of the section involves asynchronous operations.
  • Use RenderSection for sections that only contain static content or operations that are inherently synchronous.
  • Always handle the case where a section may not be defined, particularly if you’ve marked a section as not required, to avoid runtime errors.
Use Cases of Sections in Layout View in ASP.NET Core MVC

Sections in ASP.NET Core MVC layout views are powerful tools for creating flexible and customizable layouts. They allow you to inject dynamic content into specific sections of your layout from individual views. Here are some common use cases for using sections:

  1. Page-Specific Title and Meta Tags: You can use sections to inject page-specific titles, meta tags, and other SEO-related content into the <head> section of your layout. This is especially useful for improving search engine optimization.
  2. Custom Styles and Scripts: Sections are ideal for injecting page-specific CSS stylesheets and JavaScript files. This allows you to include only the necessary resources for each view, enhancing performance.
  3. Page-Level Scripts: If a particular view requires specific JavaScript code, you can use a section to inject the scripts directly into the layout’s <body> section.
  4. Additional Head Content: Apart from title and meta tags, you might have other <head> content unique to certain views. Sections enable you to add that content dynamically.
  5. Custom Sidebar Widgets: If you have a sidebar that contains dynamic widgets, you can use a section to insert those widgets into the layout.
  6. Custom Headers and Footers: You might want to customize headers and footers on a per-page basis. Sections allow you to inject page-specific content while keeping the overall structure consistent.
  7. Conditional Elements: If you need to display different elements on different pages (e.g., banners, call-to-action buttons), you can use sections to inject those elements conditionally.
  8. Mobile/Desktop Versions: For responsive designs, sections can help you provide different content or layouts for mobile and desktop versions of your site.
  9. Content Blocks: In cases where you want to provide flexible content blocks that can be inserted in different places of the layout, sections can be useful.
Need for Sections in a Layout View in ASP.NET Core MVC

In ASP.NET Core MVC, the use of sections in a layout view is a powerful feature for organizing and managing the content of web pages in a flexible and modular way. Sections allow developers to define specific areas within a layout that can be dynamically filled with different content across various views. Here are several reasons why sections are essential in a layout view:

  • Content Organization: Sections help in organizing content logically across different parts of the layout. For example, you might have sections for headers, footers, sidebars, and main content areas, which can be independently populated in different views.
  • Reusability: A single layout can be used across multiple views, with sections allowing for customization of content in those views. This means that while the overall page structure remains consistent, the content of specific sections can change, promoting code reusability and consistency across the application.
  • Maintainability: By separating the layout into sections, it becomes easier to maintain and update the website’s structure. Changes to a layout section are automatically reflected across all views that use that layout, reducing the need for repetitive updates and ensuring a uniform appearance.
  • Dynamic Content Loading: Sections can dynamically load content into different parts of the page. For example, you might have a section for a news feed that needs to be updated regularly or a section that displays user-specific information.
  • Flexibility: Sections provide the flexibility to include or exclude content as needed on a per-view basis. This is particularly useful for pages that might need to display additional information or functionality not present on other pages.

In the next article, I am going to discuss the _ViewStart.cshtml in ASP.NET Core MVC Application. In this article, I try to explain the Sections in the layout page in the ASP.NET Core MVC Application.

5 thoughts on “Sections in Layout View in ASP.NET Core MVC”

  1. Not for publish :
    “CustomJavascript.js” within the js folder as shown in the below image.
    instead of
    “CustomJavascript.cs” within the js folder as shown in the below image.

  2. As you can see there are two overloaded versions of the RenderSection Method.
    instead of
    As you can there are two overloaded versions of the RenderSection Method.

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