RoslynCodeActionPreviewCheck.cs

using System.Composition;
using System.Threading;
using System.Threading.Tasks;
using EnvDTE;
using EnvDTE80;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.CodeRefactorings;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.VisualStudio.Shell;
using Document = Microsoft.CodeAnalysis.Document;
using Solution = Microsoft.CodeAnalysis.Solution;
using Task = System.Threading.Tasks.Task;

namespace TestsCreatorCommands
{
    [ExportCodeRefactoringProvider(RefactoringId, LanguageNames.CSharp)]
    [Shared]
    internal class TestsCreatorCommands : CodeRefactoringProvider
    {
        public const string RefactoringId = "MyAction";

        public static readonly DTE2 DTE;

        static TestsCreatorCommands()
        {
            DTE = Package.GetGlobalService(typeof(DTE)) as DTE2;
        }

        public sealed override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
        {
            var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(continueOnCapturedContext: false);
            var node = root.FindNode(context.Span);

            var dec = node as MethodDeclarationSyntax;
            if (dec == null)
                return;

            context.RegisterRefactoring(CodeAction.Create("MyAction", c => DoMyAction(context.Document, dec, c)));
        }

        private static async Task<Solution> DoMyAction(Document document, MethodDeclarationSyntax method, CancellationToken cancellationToken)
        {
            var syntaxTree = await document.GetSyntaxTreeAsync(cancellationToken);
            var root = await syntaxTree.GetRootAsync(cancellationToken);

            // some - for the question irrelevant changes, like:
            document = document.WithSyntaxRoot(root.ReplaceNode(method, method.WithIdentifier(SyntaxFactory.ParseToken(method.Identifier.Text + "Suffix"))));

            // now the DTE magic
            var preview = false; // TODO: How to check if I am in preview here?
            if (!preview)
            {
                var requestedItem = DTE.Solution.FindProjectItem(document.FilePath);
                var window = requestedItem.Open(Constants.vsViewKindCode);
                window.Activate();

                var position = method.Identifier.GetLocation().GetLineSpan().EndLinePosition;
                var textSelection = (TextSelection) window.Document.Selection;
                textSelection.MoveTo(position.Line, position.Character);
            }

            return document.Project.Solution;
        }
    }
}