dotnet/maui · error · NotImplementedException

Cannot convert " " into

Error message

Cannot convert "{value}" into {destinationType}

What it means

DateTimeTypeConverter.ConvertTo throws NotImplementedException when ConvertToDestinationType cannot handle the request for a string-sourced value. It only succeeds when the string parses as DateTime/DateOnly AND the destinationType is one ConvertToDestinationType supports. If the string fails both TryParse calls, or parses but destinationType is unsupported, it throws.

Solutions

1. Ensure the source string is invariant-culture ISO 8601 parseable.
2. Ensure destinationType is string, DateTime, or DateOnly.
3. Pass a DateTime/DateOnly instance instead of a string so the typed ConvertToDestinationType overload handles it.

Example fix

// before
converter.ConvertTo(null, CultureInfo.InvariantCulture, "tomorrow", typeof(DateTime)); // unparseable -> throws

// after
converter.ConvertTo(null, CultureInfo.InvariantCulture, DateTime.Today.AddDays(1), typeof(string));

static readonly HashSet<Type> _ok = new() { typeof(string), typeof(DateTime), typeof(DateOnly) };
bool CanConvertTo(Type dest) => _ok.Contains(dest);

When it happens

Trigger: Calling ConvertTo with a string value that is not a parseable date, or a parseable date whose destinationType is neither string, DateTime, nor DateOnly (via the string branch).

Common situations: Serialization/designer code requesting conversion to an InstanceDescriptor or other Type; passing an unparseable date string through the ConvertTo path.

Related errors

• Cannot convert " " into
• Cannot convert " " into
• Cannot convert " " into
• XC0040
• Cannot convert " " into

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/747a83bbea6830b2. Report an issue: GitHub.

Appendix: source

Thrown at src/Controls/src/Core/DateTimeTypeConverter.cs:64

            return ConvertToDestinationType(dateOnly, destinationType, culture);
        }
        else if (value is DateTime dateTime)
        {
            return ConvertToDestinationType(dateTime, destinationType, culture);
        }
        else if (value is string stringValue)
        {
            if (DateTime.TryParse(stringValue, CultureInfo.InvariantCulture, DateTimeStyles.None, out dateTime))
            {
                return ConvertToDestinationType(dateTime, destinationType, culture);
            }
            else if (DateOnly.TryParse(stringValue, CultureInfo.InvariantCulture, out dateOnly))
            {
                return ConvertToDestinationType(dateOnly, destinationType, culture);
            }
        }

        throw new NotImplementedException($"Cannot convert \"{value}\" into {destinationType}");
    }

    static object ConvertToDestinationType(DateOnly dateOnly, Type? destinationType, CultureInfo? culture)
    {
        if (destinationType == typeof(string))
        {
            return dateOnly.ToString( CultureInfo.InvariantCulture);
        }
        else if (destinationType == typeof(DateTime))
        {
            return dateOnly.ToDateTime(TimeOnly.MinValue);
        }
        else if (destinationType == typeof(DateOnly))
        {
            return dateOnly;
        }

        throw new NotImplementedException($"Cannot convert \"{dateOnly}\" into {destinationType}");

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