I believe this method is not available in V8

I think you have to inject the INotificationService interface in your ctor. In Umbraco 8 everything can be 'injected', so where v7 contains some hard binded things, in v8 things are more seperated, so I think you can inject the notifications service when you would like to use it.

Try something like this:

public class ContentServiceHelper
{
    private readonly IContentService _contentService;
    private readonly IUmbracoContextAccessor _umbracoContextAccessor;
    private readonly INotificationService _notificationService;

    public ContentServiceHelper(IContentService contentService, IUmbracoContextAccessor umbracoContextAccessor, INotificationService notificationService)
    {
        _contentService = contentService;
        _umbracoContextAccessor = umbracoContextAccessor;
        _notificationService = notificationService;
    }

    public IContent CreateContent(string name)
    {
        var content = _contentService.CreateContent(name, -1, DocType.ModelTypeAlias);

        var result = _contentService.SaveAndPublish(content);
        if (result.Success)
        {
            IUser user = null;
            if (_umbracoContextAccessor.UmbracoContext != null)
            {
                user = _umbracoContextAccessor.UmbracoContext.Security.CurrentUser;
                if (user != null)
                {
                    _notificationService.SendNotifications(
                        user,
                        new[] { content },
                        "action",
                        "actionName",
                        new Uri("/"),
                        x => "subject",
                        x => "body"
                }
            }
        }

        return content;
    }
}

I don't have tried this code sample yet, but it maybe gives you a headstart. Also, have a look at the source code of Umbraco V8 at:

https://github.com/umbraco/Umbraco-CMS/blob/61cc22dccf65e3e0077f5fb93c4e0aa447abe581/src/Umbraco.Web/Compose/NotificationsComponent.cs

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