Razor Components

Since the release candidate for .NET Core 3.0 is getting closer it seemed like a good time to take a closer look at Blazor, as you can tell from the string of Blazor posts lately. For this post, I’m taking my first look at Razor Components in a Blazor server-side application.

This post is working off the same sample project used in the following posts. The first one contains the creation of the project if you want to follow along.

ASP.NET Core Server-Side Blazor with Authentication
Blazor Authentication: Hide a Nav Menu Item

What are Razor Components?

To quote the docs:

A component is a self-contained chunk of user interface (UI), such as a page, dialog, or form. A component includes HTML markup and the processing logic required to inject data or respond to UI events. Components are flexible and lightweight. They can be nested, reused, and shared among projects.

Basically, Razor Components gives us a way to create smart reusable chunks of UI.

Create a new Razor Component

To start I created a new Components directory in my project. This isn’t required, but it was how one of the Blazor sample projects were set up. Caution, if you do follow this path make sure and add the new namespace to _Imports.razor or your components will fail to render. Please don’t ask how long it took for me to figure that out.

@using System.Net.Http
@using Microsoft.AspNetCore.Components.Forms
@using Microsoft.AspNetCore.Components.Layouts
@using Microsoft.AspNetCore.Components.Routing
@using Microsoft.JSInterop
@using BlazorAuth
@using BlazorAuth.Shared
@using BlazorAuth.Components

Right-click on the directory you want to create the component in and select Add > New Item.

In the Add New Item dialog select Razor Component, give the component a name and click Add.

The resulting file will look like the following.

<h3>HelloWorld</h3>

@code {

}

For this component, I don’t have any code so I deleted that section and added space between Hello and World. To use this component you can add <HelloWorld /> to any of your existing components or pages. For example, in the sample application, I changed the Index.razor to include the new component.

@page "/"

Welcome to your new app.

<HelloWorld />

The above will render as the following.

A Component with a Parameter

The above is great, but we all know that a component that only contains static HTML isn’t going to be super useful without the ability to make parts of the component more dynamic. The following example is only one of the ways to get data into a component.

The following bit of code is a new component that has a private name property that is marked with the Parameter attribute. This property can then be used in the non-code section of the component in the standard Razor syntax way.

<h3>Hello @Name!</h3>

@code {
    [Parameter]
    private string Name {get; set;}
}

The following is the usage of the HelloName component back in the Index.razor and is passing in a name via the name parameter.

@page "/"

Welcome to your new app.

<HelloWorld />
<HelloName Name="Eric" />

And the resulting output when the application is run.

Wrapping Up

Components provide a great unit of reusability. I highly recommend you take some time to play around with them. Also, make sure and check out the Create and use ASP.NET Core Razor components doc from Microsoft as it covers the full range of options when developing components.