dotnet/wpf · error · InvalidOperationException

SR.Format(SR.NameScopeNotFound, name, "unregister")

Error message

SR.Format(SR.NameScopeNotFound, name, "unregister")

What it means

FrameworkContentElement.UnregisterName mirrors RegisterName: it needs the element's FindNameScope to return a NameScope from which the name is removed. When no namescope exists, InvalidOperationException with NameScopeNotFound("unregister") is thrown.

Solutions

Guard with NameScope.GetNameScope(element) != null before unregistering.
Unregister names while the element is still attached to its namescope-bearing tree.
Skip the call when the whole tree/scope is being discarded, since the registrations die with it.

Example fix

// before
para.UnregisterName("p1"); // may throw when detached
// after
if (NameScope.GetNameScope(para)?.FindName("p1") != null)
    para.UnregisterName("p1");

Defensive patterns

Strategy: type-guard

Validate before calling

if (NameScope.GetNameScope(element) == null) return; // nothing to unregister
element.UnregisterName(name);

Type guard

static bool HasNameScope(FrameworkContentElement e) => NameScope.GetNameScope(e) != null;

Try / catch

try { element.UnregisterName(name); } catch (InvalidOperationException ex) when (ex.Message.Contains("unregister")) { /* element detached; skip */ }

Prevention

Unregister names while the element is still attached to its namescope-bearing tree.
Check the namescope exists before unregistering; silently skip when detached.
Centralize name registration/unregistration in one helper that manages scope lifecycle.

When it happens

Trigger: Calling UnregisterName(name) on a FrameworkContentElement that is detached from any XAML tree or was never given a namescope.

Common situations: Cleanup code unregistering names on elements already removed from the visual/logical tree (scope dropped); teardown paths running after the document/page unloaded.

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/e5528ed57405c165. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Generated/FrameworkContentElement.cs:89

                throw new InvalidOperationException(SR.Format(SR.NameScopeNotFound, name, "register"));
            }
        }

        /// <summary>
        /// Unregisters the name - element combination from the
        /// NameScope that the current element belongs to.
        /// </summary>
        /// <param name="name">Name of the element</param>
        public void UnregisterName(string name)
        {
            INameScope nameScope = FrameworkElement.FindScope(this);
            if (nameScope != null)
            {
                nameScope.UnregisterName(name);
            }
            else
            {
                throw new InvalidOperationException(SR.Format(SR.NameScopeNotFound, name, "unregister"));
            }
        }

        /// <summary>
        /// Find the object with given name in the
        /// NameScope that the current element belongs to.
        /// </summary>
        /// <param name="name">string name to index</param>
        /// <returns>context if found, else null</returns>
        public object FindName(string name)
        {
            DependencyObject scopeOwner;
            return FindName(name, out scopeOwner);
        }

        // internal version of FindName that returns the scope owner
        internal object FindName(string name, out DependencyObject scopeOwner)
        {

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