dotnet/wpf · error · ArgumentException

SR.InvalidParameterValuePair

Error message

SR.InvalidParameterValuePair

What it means

Each parameter must be of the form name=value. ParseParameterAndValue locates '=' and throws ArgumentException(SR.InvalidParameterValuePair) if there is no '=', the '=' is the first character (empty name), or it is the last character (empty value).

Solutions

  1. Ensure every parameter has both a non-empty name and value: name=value.
  2. Validate each parameter with: int i = p.IndexOf('='); if (i <= 0 || i == p.Length-1) reject.
  3. Quote values containing special characters, e.g. charset="utf-8" where grammar requires.

Example fix

// before
var ct = new ContentType("text/plain; charset");
// after
var ct = new ContentType("text/plain; charset=utf-8");
Defensive patterns

Strategy: validation

Validate before calling

public static bool ParametersWellFormed(string s)
{
    foreach (var p in s.Split(';', StringSplitOptions.RemoveEmptyEntries).Skip(1))
    {
        var t = p.Trim();
        int i = t.IndexOf('=');
        if (i <= 0 || i == t.Length - 1) return false;
    }
    return true;
}

Try / catch

try { var ct = new ContentType(value); }
catch (ArgumentException ex) when (ex.Message.Contains("parameter"))
{ /* reject input or repair the name=value pair */ }

Prevention

When it happens

Trigger: new ContentType("text/plain; charset") (no '='), "text/plain; =utf8" (empty name), "text/plain; charset=" (empty value).

Common situations: Truncated strings from logs/config, key-only parameters copied from other formats, accidental deletion of a value during editing.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9e79a869cf85c101. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/ContentType.cs:452

                    throw new ArgumentException(SR.ExpectingSemicolon);

                //At this point if we have just one semicolon, then its an error.
                //Also, there can be no trailing LWS characters, as we already checked for that
                //in the constructor.
                if (parameterAndValue.Length == 1)
                    throw new ArgumentException(SR.ExpectingParameterValuePairs);

                //Removing the leading ; from the string
                parameterAndValue = parameterAndValue.Slice(1);

                //okay to trim start as there can be spaces before the begining
                //of the parameter name.
                parameterAndValue = parameterAndValue.TrimStart(_linearWhiteSpaceChars);

                int equalSignIndex = parameterAndValue.IndexOf(_equalSeparator);

                if (equalSignIndex <= 0 || equalSignIndex == (parameterAndValue.Length - 1))
                    throw new ArgumentException(SR.InvalidParameterValuePair);

                int parameterStartIndex = equalSignIndex + 1;

                //Get length of the parameter value
                int parameterValueLength = GetLengthOfParameterValue(parameterAndValue, parameterStartIndex);

                EnsureParameterDictionary();

                _parameterDictionary.Add(
                    ValidateToken(parameterAndValue.Slice(0, equalSignIndex).ToString()),
                    ValidateQuotedStringOrToken(parameterAndValue.Slice(parameterStartIndex, parameterValueLength).ToString()));

                parameterAndValue = parameterAndValue.Slice(parameterStartIndex + parameterValueLength).TrimStart(_linearWhiteSpaceChars);
            }
        }

        /// <summary>
        /// This method returns the length of the first parameter value in the input string.

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