dotnet/wpf · error · InvalidOperationException

SR.ValidationRule_UnexpectedValue

Error message

SR.ValidationRule_UnexpectedValue

What it means

DataErrorValidationRule.Validate expects the value being validated to be a BindingGroup (it validates the whole item via IDataErrorInfo). If the value is anything else, it throws InvalidOperationException(SR.Format(SR.ValidationRule_UnexpectedValue, this, value)) because the rule cannot interpret it.

Solutions

1. Add the DataErrorValidationRule to the BindingGroup's ValidationRules (or use ItemLevel validation via ValidatesOnDataErrors on the binding's data item context).
2. For per-property IDataErrorInfo validation, rely on ValidatesOnDataErrors=true on the Binding rather than manually adding the rule.
3. If calling Validate programmatically, pass the BindingGroup value the rule expects.
4. Verify the validation pipeline stage: this rule runs at UpdateSource/commit level, not per-keypress property conversion.

Example fix

// before
binding.ValidationRules.Add(DataErrorValidationRule.Instance); // wrong place
// after
binding.ValidatesOnDataErrors = true; // or add rule to BindingGroup.ValidationRules

// pass a BindingGroup to Validate, or attach the rule at the right level
bool isBindingGroupValue = value is BindingGroup;

static bool CanRunDataErrorRule(object value) => value is System.Windows.Data.BindingGroup;

try
{
    var result = DataErrorValidationRule.Instance.Validate(value, culture);
}
catch (InvalidOperationException)
{
    // rule got a per-property value; use ValidatesOnDataErrors on the Binding instead
}

When it happens

Trigger: Using DataErrorValidationRule (or ValidatesOnDataErrors) in a Binding whose ValidationRules run on an individual property value instead of a BindingGroup context — i.e., attaching the rule to a plain binding rather than a BindingGroup, or calling Validate directly with a non-BindingGroup value.

Common situations: Adding DataErrorValidationRule to a per-property Binding.ValidationRules instead of BindingGroup.ValidationRules, calling rule.Validate manually with a raw property value, or custom validation pipelines reusing the rule incorrectly.

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

• Bracket characters cannot be alpha-numeric or whitespace.
• Bracket characters cannot be one of the following: '=' …
• Cannot have empty collection of DocumentPageView objects.
• index
• InvalidDrawingAttributesWidth

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/78cc750fcc124ac8. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/DataErrorValidationRule.cs:105

                        {
                            TraceData.TraceAndNotify(TraceEventType.Error,
                                            TraceData.DataErrorInfoFailed(
                                                name,
                                                idei.GetType().FullName,
                                                ex.GetType().FullName,
                                                ex.Message),
                                            bindingExpr);
                        }
                    }

                    if (!String.IsNullOrEmpty(error))
                    {
                        return new ValidationResult(false, error);
                    }
                }
            }
            else
                throw new InvalidOperationException(SR.Format(SR.ValidationRule_UnexpectedValue, this, value));

            return ValidationResult.ValidResult;
        }

        internal static readonly DataErrorValidationRule Instance = new DataErrorValidationRule();
    }
}

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