Tutorial: Create an item template

Članek
10/05/2023

With .NET, you can create and deploy templates that generate projects, files, and resources. This tutorial is part one of a series that teaches you how to create, install, and uninstall templates for use with the dotnet new command.

You can view the completed template in the .NET Samples GitHub repository.

Tip

Item templates aren't shown in the Add > New Item dialog of Visual Studio.

In this part of the series, you'll learn how to:

Create a class for an item template.
Create the template config folder and file.
Install a template from a file path.
Test an item template.
Uninstall an item template.

Prerequisites

.NET SDK 7.0.100 or a later version.

The reference article explains the basics about templates and how they're put together. Some of this information is reiterated here.
Open a terminal and navigate to a folder where you'll store and test the templates.

Important

This article is written for .NET 7. However, it also applies to .NET 6 and previous versions, with one difference: The dotnet new syntax is different. The list, search, install, and uninstall subcommands should be --list, --search, --install, and --uninstall options, respectively.

For example, the dotnet new install command in .NET 7 becomes dotnet new --install in .NET 6. Use the dotnet new --help command to see a list of all options and subcommands.

Create the required folders

This series uses a "working folder" where your template source is contained and a "testing folder" used to test your templates. The working folder and testing folder should be under the same parent folder.

First, create the parent folder, the name doesn't matter. Then, create two subfolders named working and test. Inside of the working folder, create a subfolder named content.

The folder structure should look like the following.

parent_folder
├───test
└───working
    └───content

Create an item template

An item template is a specific type of template that contains one or more files. These types of templates are useful when you already have a project and you want to generate another file, like a config file or code file. In this example, you'll create a class that adds an extension method to the string type.

In your terminal, navigate to the working\content folder and create a new subfolder named extensions.

working
└───content
    └───extensions

Navigate to the extensions folder and create a new file named StringExtensions.cs. Open the file in a text editor. This class will provide an extension method named Reverse that reverses the contents of a string. Paste in the following code and save the file:

namespace System;

public static class StringExtensions
{
    public static string Reverse(this string value)
    {
        char[] tempArray = value.ToCharArray();
        Array.Reverse(tempArray);
        return new string(tempArray);
    }
}

Now that the content of the template is finished, the next step is to create the template config.

Create the template config

In this part of the tutorial, your template folder is located at working\content\extensions.

Templates are recognized by .NET because they have a special folder and config file that exist at the root of your template folder.

First, create a new subfolder named .template.config, and enter it. Then, create a new file named template.json. Your folder structure should look like this:

working
└───content
    └───extensions
        └───.template.config
                template.json

Open the template.json with your favorite text editor and paste in the following JSON code and save it.

{
    "$schema": "http://json.schemastore.org/template",
    "author": "Me",
    "classifications": [ "Common", "Code" ],
    "identity": "ExampleTemplate.StringExtensions",
    "name": "Example templates: string extensions",
    "shortName": "stringext",
    "tags": {
      "language": "C#",
      "type": "item"
    },
    "symbols": {
      "ClassName":{
        "type": "parameter",
        "description": "The name of the code file and class.",
        "datatype": "text",
        "replaces": "StringExtensions",
        "fileRename": "StringExtensions",
        "defaultValue": "StringExtensions"
      }
    }
  }

This config file contains all the settings for your template. You can see the basic settings, such as name and shortName, but there's also a tags/type value that's set to item. This categorizes your template as an "item" template. There's no restriction on the type of template you create. The item and project values are common names that .NET recommends so that users can easily filter the type of template they're searching for.

The classifications item represents the tags column you see when you run dotnet new and get a list of templates. Users can also search based on classification tags. Don't confuse the tags property in the template.json file with the classifications tags list. They're two different concepts that are unfortunately named the same. The full schema for the template.json file is found at the JSON Schema Store and is described at Reference for template.json. For more information about the template.json file, see the dotnet templating wiki.

The symbols part of this JSON object is used to define the parameters that can be used in the template. In this case, there's one parameter defined, ClassName. The defined parameter contains the following settings:

type - This is a mandatory setting and must be set to parameter.
description - The description of the parameter, which is printed in the template help.
datatype - The type of data of the parameter value when the parameter is used.
replaces - Specifies a text value that should be replaced in all template files by the value of the parameter.
fileRename - Similar to replaces, this specifies a text value that is replaced in the names of all of the template files by the value of the parameter.
defaultValue - The default value of this parameter when the parameter isn't specified by the user.

When the template is used, the user can provide a value for the ClassName parameter, and this value replaces all occurrences of StringExtensions. If a value isn't provided, the defaultValue is used. For this template, there are two occurrences of StringExtensions: the file StringExtensions.cs and the class StringExtensions. Because the defaultValue of the parameter is StringExtensions, the file name and class name remain unchanged if the parameter isn't specified when using the template. When a value is specified, for example dotnet new stringext -ClassName MyExts, the file is renamed MyExts.cs and the class is renamed to MyExts.

To see what parameters are available for a template, use the -? parameter with the template name:

dotnet new stringext -?

Which produces the following output:

Example templates: string extensions (C#)
Author: Me

Usage:
  dotnet new stringext [options] [template options]

Options:
  -n, --name <name>       The name for the output being created. If no name is specified, the name of the output directory is used.
  -o, --output <output>   Location to place the generated output.
  --dry-run               Displays a summary of what would happen if the given command line were run if it would result in a template creation.
  --force                 Forces content to be generated even if it would change existing files.
  --no-update-check       Disables checking for the template package updates when instantiating a template.
  --project <project>     The project that should be used for context evaluation.
  -lang, --language <C#>  Specifies the template language to instantiate.
  --type <item>           Specifies the template type to instantiate.

Template options:
  -C, --ClassName <ClassName>  The name of the code file and class.
                               Type: text
                               Default: StringExtensions

Now that you have a valid .template.config/template.json file, your template is ready to be installed. In your terminal, navigate to the extensions folder and run the following command to install the template located at the current folder:

On Windows: dotnet new install .\
On Linux or macOS: dotnet new install ./

This command outputs the list of templates installed, which should include yours.

The following template packages will be installed:
   <root path>\working\content\extensions

Success: <root path>\working\content\extensions installed the following templates:
Templates                                         Short Name               Language          Tags
--------------------------------------------      -------------------      ------------      ----------------------
Example templates: string extensions              stringext                [C#]              Common/Code

Test the item template

Now that you have an item template installed, test it.

Navigate to the test folder.

Create a new console application with dotnet new console, which generates a working project you can easily test with the dotnet run command.

dotnet new console

You get output similar to the following.

The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on C:\test\test.csproj...
  Restore completed in 54.82 ms for C:\test\test.csproj.

Restore succeeded.

Run the project using the following command.
```
dotnet run
```
You get the following output.
```
Hello, World!
```
Run dotnet new stringext to generate the StringExtensions.cs file from the template.
```
dotnet new stringext
```
You get the following output.
```
The template "Example templates: string extensions" was created successfully.
```
Change the code in Program.cs to reverse the "Hello, World!" string with the extension method provided by the template.
```
Console.WriteLine("Hello, World!".Reverse());
```
Run the program again and see that the result is reversed.
```
dotnet run
```
You get the following output.
```
!dlroW ,olleH
```

Congratulations! You created and deployed an item template with .NET. In preparation for the next part of this tutorial series, uninstall the template you created. Make sure to delete all files and folders in the test folder too. This gets you back to a clean state ready for the next part of this tutorial series.

Uninstall the template

In your terminal, navigate to the extensions folder and run the following command to uninstall the templates located at the current folder:

On Windows: dotnet new uninstall .\
On Linux or macOS: dotnet new uninstall ./

This command outputs a list of the templates that were uninstalled, which should include yours.

Success: <root path>\working\content\extensions was uninstalled.

At any time, you can use dotnet new uninstall to see a list of installed template packages, including for each template package the command to uninstall it.

Next steps

In this tutorial, you created an item template. To learn how to create a project template, continue this tutorial series.

Create a project template

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