---
title: Reusable Razor UI in class libraries with ASP.NET Core
author: Rick-Anderson
description: Explains how to create reusable Razor UI using partial views in a class library in ASP.NET Core.
monikerRange: '>= aspnetcore-2.1'
ms.author: riande
ms.date: 06/28/2019
ms.custom: "mvc, seodec18"
uid: razor-pages/ui-class
---
# Create reusable UI using the Razor class library project in ASP.NET Core

By [Rick Anderson](https://twitter.com/RickAndMSFT)

Razor views, pages, controllers, page models, [Razor components](xref:blazor/class-libraries), [View components](xref:mvc/views/view-components), and data models can be built into a Razor class library (RCL). The RCL can be packaged and reused. Applications can include the RCL and override the views and pages it contains. When a view, partial view, or Razor Page is found in both the web app and the RCL, the Razor markup (*.cshtml* file) in the web app takes precedence.

This feature requires [!INCLUDE[](~/includes/2.1-SDK.md)]

[View or download sample code](https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/razor-pages/ui-class/samples) ([how to download](xref:index#how-to-download-a-sample))

## Create a class library containing Razor UI

# [Visual Studio](#tab/visual-studio)

* From the Visual Studio **File** menu, select **New** > **Project**.
* Select **ASP.NET Core Web Application**.
* Name the library (for example, "RazorClassLib") > **OK**. To avoid a file name collision with the generated view library, ensure the library name doesn't end in `.Views`.
* Verify **ASP.NET Core 2.1** or later is selected.
* Select **Razor Class Library** > **OK**.

An RCL has the following project file:

[!code-xml[Main](ui-class/samples/cli/RazorUIClassLib/RazorUIClassLib.csproj)]

# [.NET Core CLI](#tab/netcore-cli)

From the command line, run `dotnet new razorclasslib`. For example:

```console
dotnet new razorclasslib -o RazorUIClassLib
```

For more information, see [dotnet new](/dotnet/core/tools/dotnet-new). To avoid a file name collision with the generated view library, ensure the library name doesn't end in `.Views`.

---

Add Razor files to the RCL.

The ASP.NET Core templates assume the RCL content is in the *Areas* folder. See [RCL Pages layout](#afs) to create an RCL that exposes content in `~/Pages` rather than `~/Areas/Pages`.

## Referencing RCL content

The RCL can be referenced by:

* NuGet package. See [Creating NuGet packages](/nuget/create-packages/creating-a-package) and [dotnet add package](/dotnet/core/tools/dotnet-add-package) and [Create and publish a NuGet package](/nuget/quickstart/create-and-publish-a-package-using-visual-studio).
* *{ProjectName}.csproj*. See [dotnet-add reference](/dotnet/core/tools/dotnet-add-reference).

## Walkthrough: Create an RCL project and use from a Razor Pages project

You can download the [complete project](https://github.com/aspnet/AspNetCore.Docs/tree/master/aspnetcore/razor-pages/ui-class/samples) and test it rather than creating it. The sample download contains additional code and links that make the project easy to test. You can leave feedback in [this GitHub issue](https://github.com/aspnet/AspNetCore.Docs/issues/6098) with your comments on download samples versus step-by-step instructions.

### Test the download app

If you haven't downloaded the completed app and would rather create the walkthrough project, skip to the [next section](#create-an-rcl).

# [Visual Studio](#tab/visual-studio)

Open the *.sln* file in Visual Studio. Run the app.

# [.NET Core CLI](#tab/netcore-cli)

From a command prompt in the *cli* directory, build the RCL and web app.

```console
dotnet build
```

Move to the *WebApp1* directory and run the app:

```console
dotnet run
```

---

Follow the instructions in [Test WebApp1](#test)

## Create an RCL

In this section, an RCL is created. Razor files are added to the RCL.

# [Visual Studio](#tab/visual-studio)

Create the RCL project:

* From the Visual Studio **File** menu, select **New** > **Project**.
* Select **ASP.NET Core Web Application**.
* Name the app **RazorUIClassLib** > **OK**.
* Verify **ASP.NET Core 2.1** or later is selected.
* Select **Razor Class Library** > **OK**.
* Add a Razor partial view file named *RazorUIClassLib/Areas/MyFeature/Pages/Shared/_Message.cshtml*.

# [.NET Core CLI](#tab/netcore-cli)

From the command line, run the following:

```console
dotnet new razorclasslib -o RazorUIClassLib
dotnet new page -n _Message -np -o RazorUIClassLib/Areas/MyFeature/Pages/Shared
dotnet new viewstart -o RazorUIClassLib/Areas/MyFeature/Pages
```

The preceding commands:

* Creates the `RazorUIClassLib` RCL.
* Creates a Razor _Message page, and adds it to the RCL. The `-np` parameter creates the page without a `PageModel`.
* Creates a [_ViewStart.cshtml](xref:mvc/views/layout#running-code-before-each-view) file and adds it to the RCL.

The *_ViewStart.cshtml* file is required to use the layout of the Razor Pages project (which is added in the next section).

---

### Add Razor files and folders to the project

* Replace the markup in *RazorUIClassLib/Areas/MyFeature/Pages/Shared/_Message.cshtml* with the following code:

[!code-cshtml[Main](ui-class/samples/cli/RazorUIClassLib/Areas/MyFeature/Pages/Shared/_Message.cshtml)]

* Replace the markup in *RazorUIClassLib/Areas/MyFeature/Pages/Page1.cshtml* with the following code:

[!code-cshtml[Main](ui-class/samples/cli/RazorUIClassLib/Areas/MyFeature/Pages/Page1.cshtml)]

`@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers` is required to use the partial view (`<partial name="_Message" />`). Rather than including the `@addTagHelper` directive, you can add a *_ViewImports.cshtml* file. For example:

```console
dotnet new viewimports -o RazorUIClassLib/Areas/MyFeature/Pages
```

For more information on *_ViewImports.cshtml*, see [Importing Shared Directives](xref:mvc/views/layout#importing-shared-directives)

* Build the class library to verify there are no compiler errors:

```console
dotnet build RazorUIClassLib
```

The build output contains *RazorUIClassLib.dll* and *RazorUIClassLib.Views.dll*. *RazorUIClassLib.Views.dll* contains the compiled Razor content.

### Use the Razor UI library from a Razor Pages project

# [Visual Studio](#tab/visual-studio)

Create the Razor Pages web app:

* From **Solution Explorer**, right-click the solution > **Add** >  **New Project**.
* Select **ASP.NET Core Web Application**.
* Name the app **WebApp1**.
* Verify **ASP.NET Core 2.1** or later is selected.
* Select **Web Application** > **OK**.

* From **Solution Explorer**, right-click on **WebApp1** and select **Set as StartUp Project**.
* From **Solution Explorer**, right-click on **WebApp1** and select **Build Dependencies** > **Project Dependencies**.
* Check **RazorUIClassLib** as a dependency of **WebApp1**.
* From **Solution Explorer**, right-click on **WebApp1** and select **Add** > **Reference**.
* In the **Reference Manager** dialog, check **RazorUIClassLib** > **OK**.

Run the app.

# [.NET Core CLI](#tab/netcore-cli)

Create a Razor Pages web app and a solution file containing the Razor Pages app and the RCL:

```console
dotnet new webapp -o WebApp1
dotnet new sln
dotnet sln add WebApp1
dotnet sln add RazorUIClassLib
dotnet add WebApp1 reference RazorUIClassLib
```

Build and run the web app:

```console
cd WebApp1
dotnet run
```

---

<a name="test"></a>

### Test WebApp1

Verify the Razor UI class library is in use:

* Browse to `/MyFeature/Page1`.

## Override views, partial views, and pages

When a view, partial view, or Razor Page is found in both the web app and the RCL, the Razor markup (*.cshtml* file) in the web app takes precedence. For example, add *WebApp1/Areas/MyFeature/Pages/Page1.cshtml* to WebApp1, and Page1 in the WebApp1 will take precedence over Page1 in the RCL.

In the sample download, rename *WebApp1/Areas/MyFeature2* to *WebApp1/Areas/MyFeature* to test precedence.

Copy the *RazorUIClassLib/Areas/MyFeature/Pages/Shared/_Message.cshtml* partial view to *WebApp1/Areas/MyFeature/Pages/Shared/_Message.cshtml*. Update the markup to indicate the new location. Build and run the app to verify the app's version of the partial is being used.

<a name="afs"></a>

### RCL Pages layout

To reference RCL content as though it is part of the web app's *Pages* folder, create the RCL project with the following file structure:

* *RazorUIClassLib/Pages*
* *RazorUIClassLib/Pages/Shared*

Suppose *RazorUIClassLib/Pages/Shared* contains two partial files: *_Header.cshtml* and *_Footer.cshtml*. The `<partial>` tags could be added to *_Layout.cshtml* file:

```cshtml
<body>
  <partial name="_Header">
  @RenderBody()
  <partial name="_Footer">
</body>
```

::: moniker range=">= aspnetcore-3.0"

## Create an RCL with static assets

An RCL may require companion static assets that can be referenced by the consuming app of the RCL. ASP.NET Core allows creating RCLs that include static assets that are available to a consuming app.

To include companion assets as part of an RCL, create a *wwwroot* folder in the class library and include any required files in that folder.

When packing an RCL, all companion assets in the *wwwroot* folder are included in the package automatically and are made available to apps referencing the package.

### Consume content from a referenced RCL

The files included in the *wwwroot* folder of the RCL are exposed to the consuming app under the prefix `_content/{LIBRARY NAME}/`. For example, a library named *Razor.Class.Lib* results in a path to static content at `_content/Razor.Class.Lib/`.

The consuming app references static assets provided by the library with `<script>`, `<style>`, `<img>`, and other HTML tags. The consuming app must have [static file support](xref:fundamentals/static-files) enabled.

### Multi-project development flow

When the consuming app runs:

* The assets in the RCL stay in their original folders. The assets aren't moved to the consuming app.
* Any change within the RCL's *wwwroot* folder is reflected in the consuming app after the RCL is rebuilt and without rebuilding the consuming app.

When the RCL is built, a manifest is produced that describes the static web asset locations. The consuming app reads the manifest at runtime to consume the assets from referenced projects and packages. When a new asset is added to an RCL, the RCL must be rebuilt to update its manifest before a consuming app can access the new asset.

### Publish

When the app is published, the companion assets from all referenced projects and packages are copied into the *wwwroot* folder of the published app under `_content/{LIBRARY NAME}/`.

::: moniker-end