dotnet/wpf · error · InvalidOperationException

SR.Format(SR.InvalidPropertyValue, _value, _property.Name)

Error message

SR.Format(SR.InvalidPropertyValue, _value, _property.Name)

What it means

During Trigger.Seal(), if Property is set, the framework validates that the condition Value is a valid value for that dependency property via IsValidValue. An out-of-domain value (wrong type or outside enum coercion) throws InvalidOperationException with SR.InvalidPropertyValue showing the value and property name.

Solutions

Set a Value whose type matches the property (e.g. 0.5 for Opacity, proper enum member for enums).
Use the property's type converter to convert strings first (e.g. TypeDescriptor.GetConverter(prop.PropertyType).ConvertFromString(s)) and verify IsValidValue yourself.
Validate before sealing: if (!prop.IsValidValue(value)) fix or reject the value.

Example fix

// before
trigger.Property = UIElement.OpacityProperty;
trigger.Value = "high"; // throws on Seal
// after
trigger.Property = UIElement.OpacityProperty;
trigger.Value = 0.5;

Defensive patterns

Strategy: validation

Validate before calling

if (trigger.Property != null && !trigger.Property.IsValidValue(value))
    throw new InvalidOperationException($"{value} is not valid for {trigger.Property.Name}");

Type guard

static bool IsValidFor(Trigger t) => t.Property == null || t.Property.IsValidValue(t.Value);

Try / catch

try { style.Seal(); /* or trigger seal via style use */ }
catch (InvalidOperationException ex) { log.Error($"Trigger condition invalid: {ex.Message}"); }

Prevention

Match value type to the dependency property's type exactly
Convert strings with the property's TypeConverter before assigning
Call DependencyProperty.IsValidValue as a pre-flight check

When it happens

Trigger: trigger.Property = UIElement.OpacityProperty; trigger.Value = "high"; then Seal()/style application — the string is not a valid double for Opacity. Also enum values of the wrong enum type.

Common situations: Assigning a value of the wrong type for the property (string where double/enum expected); copy-pasting values across properties; values typed from parsed config strings.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9df0164580fb2c29. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Trigger.cs:199

                throw new ArgumentException(SR.Format(SR.UnexpectedParameterType, o.GetType(), typeof(Setter)), nameof(o));
            }

            return setter;
        }

        internal sealed override void Seal()
        {
            if (IsSealed)
            {
                return;
            }

            if (_property != null)
            {
                // Ensure valid condition
                if (!_property.IsValidValue(_value))
                {
                    throw new InvalidOperationException(SR.Format(SR.InvalidPropertyValue, _value, _property.Name ));
                }
            }

            // Freeze the condition for the trigger
            StyleHelper.SealIfSealable(_value);

            // Process the _setters collection: Copy values into PropertyValueList and seal the Setter objects.
            ProcessSettersCollection(_setters);

            // Build conditions array from collection
            TriggerConditions = new TriggerCondition[] {
                new TriggerCondition(
                    _property,
                    LogicalOp.Equals,
                    _value,
                    _sourceName ?? StyleHelper.SelfName) };

            // Set Condition for all property triggers

View on GitHub (pinned to 81131a70a4)