dotnet/wpf · error · ArgumentException

SR.Format(SR.ConditionValueOfMarkupExtensionNotSupported…

Error message

SR.Format(SR.ConditionValueOfMarkupExtensionNotSupported, value.GetType().Name)

What it means

The DataTrigger.Value setter rejects MarkupExtension instances with ArgumentException. Markup extensions (like Binding or StaticResource) are deferred values that the condition system cannot evaluate as a literal comparison value. Use Binding on the trigger for dynamic conditions and keep Value a literal.

Solutions

1. Put the dynamic part in DataTrigger.Binding and compare against a literal Value
2. Use a plain CLR value (string, number, enum) for Value
3. If deferred lookup is needed, resolve the resource to a concrete value before assignment

Example fix

// before
trigger.Value = new Binding("Threshold"); // throws
// after
trigger.Binding = new Binding("Amount");
trigger.Value = 100;

if (value is MarkupExtension) throw new ArgumentException("DataTrigger.Value cannot be a MarkupExtension; use Binding instead", nameof(value));

bool IsValidTriggerValue(object v) => v is not MarkupExtension;

try { trigger.Value = candidate; } catch (ArgumentException) { /* move dynamic logic to trigger.Binding */ }

When it happens

Trigger: Assigning e.g. trigger.Value = new Binding(...) or another MarkupExtension-derived object to DataTrigger.Value.

Common situations: Copy-pasting XAML semantics into code (thinking Value can be a binding); attempting dynamic condition values instead of using the trigger's Binding.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• SR.ConditionValueOfExpressionNotSupported
• ' ' is not a valid value for ' '.
• ArgumentException(message, name)
• ArgumentNullException(name)
• ArgumentOutOfRangeException(authentication)

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/354be89c75737766. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/DataTrigger.cs:77

            {
                // Verify Context Access
                VerifyAccess();

                return _value;
            }
            set
            {
                // Verify Context Access
                VerifyAccess();

                if (IsSealed)
                {
                    throw new InvalidOperationException(SR.Format(SR.CannotChangeAfterSealed, "DataTrigger"));
                }

                if (value is MarkupExtension)
                {
                    throw new ArgumentException(SR.Format(SR.ConditionValueOfMarkupExtensionNotSupported,
                                                       value.GetType().Name));
                }

                if( value is Expression )
                {
                    throw new ArgumentException(SR.ConditionValueOfExpressionNotSupported);
                }

                _value = value;
            }
        }

        /// <summary>
        ///     Collection of Setter objects, which describes what to apply
        /// when this trigger is active.
        /// </summary>
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
        public SetterBaseCollection Setters

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