dotnet/wpf · error · XamlSchemaException

' '.' ' is a property without a getter and is not a valid…

Error message

'{0}'.'{1}' is a property without a getter and is not a valid XAML property.

What it means

ClrProperty wraps a CLR PropertyInfo for XAML schema use. It demands a getter: if pi.GetGetMethod(true) returns null the property is write-only, which is not a valid XAML property, so a XamlSchemaException (SR.SetOnlyProperty) is thrown naming declaringType and the property.

Solutions

Add a getter to the property (it can be less accessible, e.g. private, but must exist).
Replace the set-only property with a public field or a full property.
Point the XAML schema at a different member that is readable.

Example fix

// before
public string Secret { set { _secret = value; } }
// after
public string Secret { get; set; }
// or keep setter private getter:
public string Secret { private get; set; }

Defensive patterns

Strategy: type-guard

Validate before calling

// before using a property in XAML
if (propInfo.GetGetMethod(true) == null)
    throw new InvalidOperationException($"{propInfo.DeclaringType}.{propInfo.Name} is write-only; add a getter");

Type guard

bool IsReadable(PropertyInfo p) => p.GetGetMethod(true) != null;
bool IsXamlUsable(PropertyInfo p) => p.CanRead || p.CanWrite && p.GetGetMethod(true) != null;

Try / catch

try { member = new ClrProperty(name, propInfo, declaringType, schemaContext); }
catch (XamlSchemaException ex) { log($"Write-only property: {ex.Message}"); }

Prevention

Never declare set-only properties on XAML-exposed types.
If the getter must be hidden, make it private/internal rather than omitting it.
Scan assemblies for CanRead == false properties before XAML use.

When it happens

Trigger: Constructing ClrProperty from a PropertyInfo that has no get accessor at all (public or private), e.g. a property with only a set accessor.

Common situations: Write-only properties in view-models or custom markup-extension targets referenced from XAML; code-generation emitting set-only properties; languages/platforms where GetGetMethod(true) still returns null because no getter was declared.

Understand the failure class

Background: "not installed", "pip install", "required for": how missing-dependency errors surface across open-source libraries — this error's family across 34 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e8fd7e62a5afd99f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/Schema/ClrProperty.cs:80

        public ClrProperty(string name, PropertyInfo pi, XamlType declaringType)
            : this(name, pi, declaringType, false)
        {
        }

        private ClrProperty(string name, PropertyInfo pi, XamlType declaringType, bool isStatic)
        {
            Debug.Assert(pi != null);
            Debug.Assert(pi.Name == name);
#if DEBUG
            if (declaringType == null)
            {
                throw new XamlInternalException("Asserting that the declaringType should never be null");
            }
#endif
            MethodInfo mi = pi.GetGetMethod(true);
            if (mi == null)
            {
                throw new XamlSchemaException(SR.Format(SR.SetOnlyProperty, declaringType.Name, name));
            }

            _declaringType = declaringType;
            _name = pi.Name;
            _isPublic = mi.IsPublic;
            _isReadOnly = !pi.CanWrite;
            _isStatic = isStatic;
            ClrBindingPropertyInfo = pi;

            _isAttachable = false;
            _isEvent = false;

            OtherInitialization();
        }



        private void OtherInitialization()

View on GitHub (pinned to 81131a70a4)