Causes of Unhandled Exception: FormatException: Unexpected end of input
- Incomplete Data Received: This exception often occurs when the parser encounters an unexpected end of the input, which generally means that the code is expecting more data than it received. If you are parsing JSON, a common situation is that the device or network fetches incomplete JSON data. For instance, a network request may be successfully initiated but truncated unexpectedly due to connectivity issues.
- Improper JSON Structure: If the JSON structure lacks closing brackets or commas, it will lead to an unexpected end of input. An incorrect structure is often the result of manually crafted JSON that doesn't adhere to the proper JSON format.
- Unanticipated Null Values: Assignments to objects or lists from an external source may sometimes result in null values within critical fields, which, in turn, creates an incomplete set of expected properties. JSON parsing, for example, can fail when trying to access data that was expected but not present.
- End of String Data: When parsing string data, the unhandled exception often signals that the parser has reached the end of the string before it successfully parsed all of the necessary input elements. For example, if certain parts of your code rely on substrings split by a specific delimiter, missing delimiters will result in an incomplete string parsing.
- Incorrect Charset Encoding: Parsing problems might arise from unexpected end of input caused by using an incorrect charset encoding or character set transformations. If character data is not encoded properly, you might see incomplete or malformed data being parsed into the application.
Example Scenario to Illustrate the Cause
void parseJson(String jsonString) {
var decodedData;
try {
decodedData = json.decode(jsonString);
} catch (e) {
print('Exception caught: $e');
}
if (decodedData != null) {
print(decodedData);
}
}
void main() {
// This JSON string is intentionally incomplete to trigger the exception
String incompleteJson = '{"name": "John", "age": 30, ';
parseJson(incompleteJson);
}
- In this example, the JSON string is incomplete because it is missing the final closing brace. This will throw a `FormatException` with the message `Unexpected end of input` because the JSON parser is expecting the string to be complete.
