Introduction
In developing a self-practice eCommerce app with Flutter and Laravel, you might encounter issues while deserializing API responses into your model classes. One such error is the infamous Unhandled Exception: type 'List. This can happen due to mismatches between your Dart models and the structure of the JSON API response.
Understanding the Issue
The error you are experiencing usually arises from improper casting or expectations about the data types returned by the API. In your case, the OrderItem class expects a List for the pid property, but your API response can sometimes return a string representation of the list instead of an actual list of numbers, especially when data validation is lacking on the server side.
The API Response
Your API response should ideally return a list of integers. However, one of your objects contains an issue:
{
"id": 2,
"uid": "1",
"pid": "[2,3]",
"created_at": "2022-07-16T12:19:15.000000Z",
"updated_at": "2022-07-16T12:19:15.000000Z"
}
As you can see, the value of pid is wrapped in quotes, making it a string rather than a list. This discrepancy in data type can lead to the error you encountered.
Step-by-Step Solution
To solve this problem, we can enhance the OrderItem.fromMap constructor to safely handle the pid property. Here’s how:
Adjusting the OrderItem Class
Modify the fromMap method within your OrderItem class to check if pid is of type String. If it is, we can parse it into a list of numbers. Here's the modified code:
factory OrderItem.fromMap(Map map) {
List parsedPid;
if (map['pid'] is String) {
// Parse json string to List
parsedPid = (json.decode(map['pid']) as List).map((e) => e as num).toList();
} else {
parsedPid = List.from(map['pid'] as List);
}
return OrderItem(
map['id'] as num,
parsedPid,
);
}
Adjusting the Orders Class
Similarly, you will need to ensure your Orders.fromMap method handles the incoming data correctly:
factory Orders.fromMap(Map map) {
return Orders(
List.from(
(map['orders'] as List).map((x) => OrderItem.fromMap(x as Map)),
),
);
}
Conclusion
These modifications allow your OrderItem class to manage scenarios when the pid comes either as a list or a string representing a list. This should clear up the type casting error and allow you to properly store API responses in your data structures.
Ensure that your API is sending the correct data types where possible for best practices. Proper validation on your back-end in Laravel can help avoid these runtime exceptions in your Flutter app.
Frequently Asked Questions
What should I do if my API frequently changes data types?
When dealing with an unreliable API, consider implementing more robust error handling and validation in your model classes to accommodate unexpected formats.
How can I further debug data type issues in Dart?
Utilize debugging tools in your IDE to inspect incoming data before deserialization. Logging data before processing can also provide insight into its structure.
Is it common for APIs to return inconsistent data types?
Yes, especially during development phases. Ensuring strict data validation on the server side is critical to maintaining data integrity between client and server applications.
