dotnet/wpf · error · InvalidOperationException

SR.Format(SR.ValidationRule_UnknownStep, validationStep…

Error message

SR.Format(SR.ValidationRule_UnknownStep, validationStep, bindingGroup)

What it means

In BindingExpression.ValidateWithoutUpdate/Validate flow, the validationStep parameter selects which value object is handed to the rule (proposed values, the expression itself, etc.); the default branch throws this InvalidOperationException for any step outside the known set. Like error 2478, a closed-enum guard indicating corrupted or unsupported ValidationStep input.

Solutions

Pass only valid ValidationStep values when invoking validation
Fix enum deserialization/persistence so ValidationStep never exceeds the defined range
Update custom binding subclasses to map steps correctly before calling Validate

Example fix

// before
expr.ValidateWithoutUpdate((ValidationStep)42, bindingGroup); // throws
// after
expr.ValidateWithoutUpdate(ValidationStep.UpdatedValue, bindingGroup);

Defensive patterns

Strategy: validation

Validate before calling

if (!Enum.IsDefined(typeof(ValidationStep), validationStep)) throw new InvalidOperationException("Unknown ValidationStep");

Type guard

static bool IsSupportedStep(ValidationStep s) => Enum.IsDefined(typeof(ValidationStep), s);

Try / catch

try { Validate(value, validationStep); } catch (InvalidOperationException ex) when (ex.Message.Contains("ValidationStep")) { /* normalize step and retry */ }

Prevention

Pass only closed-set ValidationStep values in custom binding internals
Guard persisted/deserialized ValidationStep values
Map custom steps onto the four standard ValidationStep members before calling engine APIs

When it happens

Trigger: Calling the internal validation path with a validationStep value not in RawProposedValue/ConvertedProposedValue/UpdatedValue/CommittedValue — via invalid enum casts, corrupted deserialized values, or custom BindingExpressionBase subclasses passing wrong steps.

Common situations: Custom binding-group/expression extensions (e.g. bespoke BindingGroup implementations) passing unexpected steps; enum deserialized from bad persisted state; framework version drift between rule and engine.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f0292a8dbc1e4da7. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/BindingExpression.cs:2105

        {
            if (!NeedsValidation)
                return true;

            object value;
            switch (validationStep)
            {
                case ValidationStep.RawProposedValue:
                    value = GetRawProposedValue();
                    break;
                case ValidationStep.ConvertedProposedValue:
                    value = bindingGroup.GetValue(this);
                    break;
                case ValidationStep.UpdatedValue:
                case ValidationStep.CommittedValue:
                    value = this;
                    break;
                default:
                    throw new InvalidOperationException(SR.Format(SR.ValidationRule_UnknownStep, validationStep, bindingGroup));
            }

            return Validate(value, validationStep);
        }

        /// <summary>
        /// Get the proposed value(s) that would be written to the source(s), applying
        /// conversion and checking UI-side validation rules.
        /// </summary>
        internal override bool ValidateAndConvertProposedValue(out Collection<ProposedValue> values)
        {
            Debug.Assert(NeedsValidation, "check NeedsValidation before calling this");
            values = null;

            // validate raw proposed value
            object rawValue = GetRawProposedValue();

            bool isValid = Validate(rawValue, ValidationStep.RawProposedValue);

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