dotnet/wpf · error · SystemException

SR.Format(SR.CustomContentStateMustBeSerializable, type)

Error message

SR.Format(SR.CustomContentStateMustBeSerializable, type)

What it means

When saving a journal entry that carries a CustomContentState, the service verifies the state object's type is serializable. Non-serializable CustomContentState objects cannot survive journal serialization (e.g. saving to disk for Remember navigation), so a SystemException is thrown naming the offending type.

Solutions

Mark the CustomContentState class [Serializable] and implement ISerializable correctly.
Ensure all fields of the CustomContentState are serializable types.
Store non-serializable data by reference/key and rebuild it in Reapply().
Test journal save/load early in development of custom state.

Example fix

// before
class MyState : CustomContentState { public MyControl C; }
// after
[Serializable]
class MyState : CustomContentState {
    public string ControlId; // serializable data instead of live control
    public override void Reapply(object navigationContent, NavigationMode mode) { ... }
}

Defensive patterns

Strategy: validation

Validate before calling

bool stateIsSerializable(CustomContentState ccs) => ccs == null || ccs.GetType().IsSerializable;

Type guard

bool IsSerializableState<T>(T state) where T : CustomContentState => state.GetType().IsSerializable;

Try / catch

try { navService.AddBackEntry(myState); }
catch (SystemException ex) when (ex.Message.Contains("serializable"))
{ /* log type and fix [Serializable] */ }

Prevention

Always mark CustomContentState subclasses [Serializable].
Keep state fields to serializable primitives.
Add a unit test that round-trips state via a BinaryFormatter/MemoryStream.
Store live controls by identifier, rebuild in Reapply.

When it happens

Trigger: Calling NavigationService.AddBackEntry / creating journal entries with a CustomContentState subclass not marked [Serializable] (and not implementing ISerializable), especially with NavigationMode.Remember navigation.

Common situations: Custom view-state class missing [Serializable] attribute; CustomContentState added in IProvideCustomContentState implementations; journal persistence paths that require serialization.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/8259d84cc6400adf. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Navigation/NavigationService.cs:3231

            // _customContentStateToSave can be preset by AddBackEntry() or FireNavigating().
            // If not, try the IProvideCustomContentState callback.
            CustomContentState ccs = _customContentStateToSave;
            if (ccs == null)
            {
                IProvideCustomContentState pccs = _bp as IProvideCustomContentState;
                if (pccs != null)
                {
                    ccs = pccs.GetContentState();
                }
            }
            if (ccs != null)
            {
                // Make sure the object is serializable
                Type type = ccs.GetType();
                if (!type.IsSerializable)
                {
                    throw new SystemException(SR.Format(SR.CustomContentStateMustBeSerializable, type));
                }
                journalEntry.CustomContentState = ccs;
            }
            // Info: CustomContentState for the current page in child frames is saved in
            // DataStreams.SaveState(). (This requires the IProvideCustomContentState to be implemented.)

            // Root Viewer journaling
            if (_rootViewerStateToSave != null) // state saved in advance?
            {
                journalEntry.RootViewerState = _rootViewerStateToSave;
                _rootViewerStateToSave = null;
            }
            else
            {
                journalEntry.RootViewerState = GetRootViewerState(journalReason);
            }

            // Set the friendly Name of this JournalEntry, it will be used to display

View on GitHub (pinned to 81131a70a4)