stride3d/stride · error · InvalidOperationException

A session is already open in this instance.

Error message

A session is already open in this instance.

What it means

EditorViewModel.NewSession creates a new SessionViewModel, but only one session may be open per editor instance. If the Session property is already non-null, it throws InvalidOperationException before creating the new session.

Solutions

1. Close the current session (set Session to null via CloseSession) before calling NewSession
2. Check EditorViewModel.Session for null before invoking NewSession
3. Disable New-session UI commands while a session is open

Example fix

// before
await editor.NewSession(parameters);
// after
if (editor.Session == null) await editor.NewSession(parameters);

if (editor.Session != null) throw new InvalidOperationException("Close the current session first");

bool CanOpenNewSession(EditorViewModel e) => e.Session == null;

try { await editor.NewSession(p); } catch (InvalidOperationException) { /* session already open */ }

When it happens

Trigger: Calling NewSession (e.g. File > New) while a session is already loaded — Session != null.

Common situations: Automation/scripts invoking new-session commands without closing the current session; UI code not disabling 'New' when a session is open.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

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AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/55eb3895d9ac6c1f. Report an issue: GitHub.

Appendix: source

Thrown at sources/editor/Stride.Core.Assets.Editor/ViewModel/EditorViewModel.cs:113

#if DEBUG
        public ICommandBase DebugCommand { get; }
#endif

        // Temporary, until we integrate a proper text editor in the studio
        protected internal virtual IEnumerable<string> TextAssetTypes => Enumerable.Empty<string>();

#if DEBUG
        public void DebugFunction()
        {
            Console.WriteLine(@"DebugFunction invoked");
        }
#endif

        public async Task<bool> NewSession(NewSessionParameters newSessionParameters)
        {
            if (Session != null)
                throw new InvalidOperationException("A session is already open in this instance.");

            var newSession = await SessionViewModel.CreateNewSession(this, ServiceProvider, newSessionParameters);
            if (newSession != null)
            {
                Session = newSession;
                MRU.AddFile(Session.SolutionPath, EditorVersionMajor);
            }

            return Session != null;
        }

        public async Task<bool?> OpenInitialSession(string initialSessionPath)
        {
            if (string.IsNullOrWhiteSpace(initialSessionPath))
                return false;

            // The LoadingStartupSession settings is true, which means that the editor crashed while loading the startup project last time.
            // Lets give the user a chance to fix the startup session.

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