dotnet/wpf · error · KeyNotFoundException

SR.Format(SR.DirectiveNotFound, name, this.TargetNamespace)

Error message

SR.Format(SR.DirectiveNotFound, name, this.TargetNamespace)

What it means

XaslNamespace.GetDirectiveType looks up a directive name in its DirectiveTypes dictionary and throws KeyNotFoundException(SR.Format(SR.DirectiveNotFound, name, TargetNamespace)) when the directive is not registered. The code comment notes this is an early-version behavior and the error path is expected to improve.

Solutions

  1. Fix the directive name in the XAML or call site to match a registered directive for this TargetNamespace.
  2. Verify the XaslNamespace instance you are querying actually owns the directive (check TargetNamespace in the message).
  3. Use GetAllDirectiveTypes() first to enumerate valid names before lookup.
  4. Wrap the lookup in try/catch for KeyNotFoundException if unknown directives are expected.

Example fix

// before
var t = xamlNamespace.GetDirectiveType("x:Shareable");
// after
var t = xamlNamespace.GetAllDirectiveTypes().Any(d => /* name matches */)
    ? xamlNamespace.GetDirectiveType("x:Shared")
    : null;
Defensive patterns

Strategy: validation

Validate before calling

bool exists = xamlNamespace.GetAllDirectiveTypes()
    .Any(d => /* d matches requested name */);
if (!exists) throw new ArgumentException($"Unknown directive '{name}' in {xamlNamespace.TargetNamespace}");

Try / catch

try { var t = ns.GetDirectiveType(name); } catch (KeyNotFoundException ex) { /* handle unknown directive for ns.TargetNamespace */ }

Prevention

When it happens

Trigger: Requesting a directive XamlType via GetDirectiveType(name) where name is not present in the namespace's DirectiveTypes, e.g. a typo'd directive like 'x:Ky' or a directive from a different xaml namespace.

Common situations: Hand-written XAML with misspelled x: directives; parsing documents referencing directives from a namespace whose XaslNamespace was built without that directive registered; version drift where a directive was added in a newer schema.

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/7964f5a0795985a1. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Schema/XaslNamespace.cs:114

                {
                    return null;
                }
            }
            return xaslType;
        }

        public override IEnumerable<XamlType> GetAllXamlTypes()
        {
            return this.Types as IEnumerable<XamlType>;
        }

        public override XamlType GetDirectiveType(string name)
        {
            XaslType dirType = null;
            if (!DirectiveTypes.TryGetValue(name, out dirType))
            {
                // throw in the early versions, do something better for error path.
                throw new KeyNotFoundException(SR.Format(SR.DirectiveNotFound, name, this.TargetNamespace));
            }
            return dirType;
        }

        public override IEnumerable<XamlType> GetAllDirectiveTypes()
        {
            return DirectiveTypes as IEnumerable<XamlType>;
        }

        public override XamlProperty GetDirectiveProperty(string name)
        {
            XaslMember dirProperty = null;
            if (!DirectiveProperties.TryGetValue(name, out dirProperty))
            {
                // throw in the early versions, do something better for error path.
                throw new KeyNotFoundException(SR.Format(SR.DirectiveNotFound, name, this.TargetNamespace));
            }
            return dirProperty;

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