dotnet/aspnetcore · error · InvalidOperationException

Cannot notify about changes because the

Error message

Cannot notify about changes because the {GetType()} is configured as fixed.

What it means

CascadingValueSource created with isFixed=true is designed to never change. Calling NotifyChangedAsync on it is a programming error because fixed sources skip subscription tracking, so there is nothing to notify.

Solutions

Create the source with isFixed: false if you need change notifications.
Remove the NotifyChangedAsync call on the fixed source.
If the value must change, replace the source instance entirely instead of notifying.

Example fix

// before
var src = new CascadingValueSource<string>("v", isFixed: true);
await src.NotifyChangedAsync();
// after
var src = new CascadingValueSource<string>("v", isFixed: false);
src.Value = "v2";
await src.NotifyChangedAsync();

Defensive patterns

Strategy: validation

Validate before calling

// Track whether the source is fixed and skip notify calls accordingly.
if (!sourceIsFixed)
{
    await source.NotifyChangedAsync();
}

Prevention

Choose isFixed=false at construction if you ever intend to notify.
Encapsulate notify calls behind a helper that checks the fixed flag.
Unit-test fixed sources to ensure NotifyChangedAsync is never called on them.

When it happens

Trigger: new CascadingValueSource<T>(value, isFixed: true) followed by a call to .NotifyChangedAsync().

Common situations: Refactoring a non-fixed source to fixed without removing notify calls, copying code from a dynamic source, or misunderstanding the isFixed contract.

Related errors

AI-assisted analysis of dotnet/aspnetcore@3600ca084e (2026-08-11). Data as JSON: /api/errors/da48d3cee1cc3869. Report an issue: GitHub.

Appendix: source

Thrown at src/Components/Components/src/CascadingValueSource.cs:89

    private CascadingValueSource(bool isFixed)
    {
        _isFixed = isFixed;

        if (!_isFixed)
        {
            _subscribers = new();
        }
    }

    /// <summary>
    /// Notifies subscribers that the value has changed (for example, if it has been mutated).
    /// </summary>
    /// <returns>A <see cref="Task"/> that completes when the notifications have been issued.</returns>
    public Task NotifyChangedAsync()
    {
        if (_isFixed)
        {
            throw new InvalidOperationException($"Cannot notify about changes because the {GetType()} is configured as fixed.");
        }

        if (_subscribers?.Count > 0)
        {
            var tasks = new List<Task>();

            foreach (var (dispatcher, subscribers) in _subscribers)
            {
                tasks.Add(dispatcher.InvokeAsync(() =>
                {
                    var subscribersBuffer = new ComponentStateBuffer();
                    var subscribersCount = subscribers.Count;
                    var subscribersCopy = subscribersCount <= ComponentStateBuffer.Capacity
                        ? subscribersBuffer[..subscribersCount]
                        : new ComponentState[subscribersCount];
                    subscribers.CopyTo(subscribersCopy);

                    // We iterate over a copy of the list because new subscribers might get

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