unoplatform/uno · error · NotImplementedException

NotImplemented_GetFormattedString

Error message

NotImplemented_GetFormattedString

What it means

Thrown by System.Json.JsonPrimitive.GetFormattedString when JsonType is String but the stored _value is neither a string, null, nor char — an internal invariant violation of the JsonPrimitive. This is a vendored copy of the .NET corefx System.Json library shipped inside Uno.UI.Lottie. It indicates a JsonPrimitive was constructed in an inconsistent state (a non-string/cl type stored under JsonType.String).

Source

Thrown at src/AddIns/Uno.UI.Lottie/System.Json/JsonPrimitive.cs:160

					stream.Write(bytes, 0, bytes.Length);
					break;
			}
		}

		internal string GetFormattedString()
		{
			switch (JsonType)
			{
				case JsonType.String:
					if (_value is string || _value == null)
					{
						return (string)_value;
					}
					if (_value is char)
					{
						return _value.ToString();
					}
					throw new NotImplementedException("NotImplemented_GetFormattedString");

				case JsonType.Number:
					string s = _value is float || _value is double ?
						((IFormattable)_value).ToString("R", CultureInfo.InvariantCulture) : // Use "round-trip" format
						((IFormattable)_value).ToString("G", CultureInfo.InvariantCulture);
					return s == "NaN" || s == "Infinity" || s == "-Infinity" ?
						"\"" + s + "\"" :
						s;

				default:
					throw new InvalidOperationException();
			}
		}
	}
}

View on GitHub (pinned to 0418340488)

Solutions

1. Do not construct JsonPrimitive with a type that conflicts with JsonType; use the typed constructors (JsonPrimitive(string), JsonPrimitive(char)).
2. If consuming third-party JSON, parse with JsonValue.Parse which sets JsonType consistently rather than hand-building primitives.
3. If you hit this in the Lottie pipeline, capture the JSON string being parsed and validate it externally — the exception implies an internal state bug, so file it against Uno.UI.Lottie with a repro.
4. Avoid mutating JsonPrimitive._value via reflection/serialization binders.

Example fix

// before — inconsistent state
var p = new JsonPrimitive(42);
typeof(JsonPrimitive).GetProperty("JsonType")!.SetValue(p, JsonType.String);
p.GetFormattedString(); // throws NotImplemented_GetFormattedString

// after — keep type and value consistent
var p = new JsonPrimitive("42"); // JsonType.String with string value
p.GetFormattedString();

bool JsonPrimitiveStringConsistent(JsonPrimitive p)
    => p.JsonType == JsonType.String && (p.Value is string or char || p.Value is null);

When it happens

Trigger: A JsonPrimitive instance whose JsonType was set to String but _value holds an incompatible CLR type (e.g. via reflection or a deserialization edge case), then GetFormattedString() is invoked during JSON serialization of a Lottie payload.

Common situations: Manipulating System.Json primitives through reflection or interop; a corrupted/hand-built Lottie JSON object tree where a node's type and value disagree; extremely rare in normal Lottie playback. Almost always a sign of programmatic misuse rather than a bad input file.

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AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/67732a7c472e18b8. Report an issue: GitHub.