Upgrade an ASP.NET Core Application to Bootstrap 4

As part of the work, I did on the application referenced in the web.config transform post from last week I also upgraded the application from Bootstrap 3 to Bootstrap 4 and this post is going to walk through a process to get the new version of Bootstrap up and running in a site.

Create a Sample Application

In case you want a project with Bootstrap 3 installed to play around with before attempting a production site the following command, run in a command prompt, will create an ASP.NET Core 2.1 application that has Bootstrap 3.

dotnet new webapp -f netcoreapp2.1

Upgrade Bootstrap Files

The first step I took was to delete the existing Bootstrap related file which can be found in the wwwroot/lib directory and delete the whole bootstrap directory.

Now open the project in Visual Studio and right-click on the project file and select Add > Client-Side Library.

The dialog that shows will allow you to search for client-side libraries to include in your application. In this case, we are looking for twitter-bootstrap. Your version number may be higher than the one shown in the screenshot below. I change the target location to match where Bootstrap was installed by the template by default, but that isn’t required. Finally, click Install.

The dialog above and the installation of the file is part of LibMan, which provides a lot of functionality for managing client-side libraries. Check out the official LibMan docs for more information.

Dealing with the Bootstrap Changes

This section is going to be really light on details as Bootstrap 4 was a reboot of Bootstrap and a ton of things changed. I will give an example or two here, but really the official Bootstrap Migrating to v4 guide is where you will want to go for all the details.

Here are a couple of examples of the type of changes you will be making.

<label asp-for="User" class="control-label"></label>

<label asp-for="User" class="col-form-label"></label>

The look of buttons has changed so where we had used default before we changed to secondary.

<input type="submit" value="Load" class="btn btn-default" />

<input type="submit" value="Load" class="btn btn-secondary" />

Wrapping Up

Hopefully, this will help you get a jump start on upgrading sites from Bootstrap 3 to Bootstrap 4. Thankfully after you get the files in the right spot Bootstrap’s migration guide should get you the rest of the way.