dotnet/wpf · error · ArgumentException

SR.NameScopeNameNotFound

Error message

SR.NameScopeNameNotFound

What it means

NameScope.UnregisterName removes a name-to-object mapping from a XAML namescope. If the name does not exist in the namescope's name map, this ArgumentException is thrown. The library treats unregistering an unknown name as a programming error rather than silently ignoring it.

Solutions

  1. Call NameScope.ContainsName(nameScope, name) (or check FindName != null) before calling UnregisterName.
  2. Wrap UnregisterName in try/catch for ArgumentException if double-unregister is expected in your cleanup logic.
  3. Verify you are operating on the correct namescope instance — names registered on an ancestor namescope are not visible here.
  4. Check that the name string exactly matches the one passed to RegisterName (case-sensitive).

Example fix

// before
nameScope.UnregisterName("okButton"); // throws if never registered

// after
if (NameScope.ContainsName(nameScope, "okButton"))
{
    nameScope.UnregisterName("okButton");
}
Defensive patterns

Strategy: validation

Validate before calling

if (NameScope.ContainsName(nameScope, name))
{
    nameScope.UnregisterName(name);
}

Try / catch

try
{
    nameScope.UnregisterName(name);
}
catch (ArgumentException ex) when (ex.Message.Contains("NameScopeNameNotFound"))
{
    // name was not registered; safe to ignore during cleanup
}

Prevention

When it happens

Trigger: Calling UnregisterName(name) on a NameScope (or element via NameScope.SetNameScope/FindName-related helpers) where `name` was never registered with RegisterName, or was already unregistered, or the namescope is empty.

Common situations: Unregistering a XAML element name twice; unregistering a name that was defined in a different namescope (e.g. templates vs page); trying to remove a name registered programmatically with a different casing; cleanup code running before registrations occurred.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/74734bb9b9724c3d. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/NameScope.cs:94

        /// <summary>
        /// Unregister Name-Object Map 
        /// </summary>
        /// <param name="name">name to be registered</param>
        public void UnregisterName(string name)
        {
            ArgumentNullException.ThrowIfNull(name);

            if (name.Length == 0)
                throw new ArgumentException(SR.NameScopeNameNotEmptyString);

            if (_nameMap != null && _nameMap[name] != null)
            {
                _nameMap.Remove(name);
            }
            else
            {
                throw new ArgumentException(SR.Format(SR.NameScopeNameNotFound, name));
            }

            if (TraceNameScope.IsEnabled)
            {
                TraceNameScope.TraceActivityItem( TraceNameScope.UnregisterName,
                                                  this, name );
            }
        }

        /// <summary>
        /// Find - Find the corresponding object given a Name
        /// </summary>
        /// <param name="name">Name for which context needs to be retrieved</param>
        /// <returns>corresponding Context if found, else null</returns>
        public object FindName(string name)
        {
            if (_nameMap == null || string.IsNullOrEmpty(name))
                return null;

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