Скачать или смотреть Resolving Dart Type Errors: Fixing the _InternalLinkedHashMap String, dynamic Issue in Flutter

Discover how to solve the "_InternalLinkedHashMap String, dynamic is not a subtype of type TodoModel" error in Flutter and improve your TodoModel class for better coding practices.
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This video is based on the question https://stackoverflow.com/q/62966315/ asked by the user 'shinyatk' ( https://stackoverflow.com/u/3011308/ ) and on the answer https://stackoverflow.com/a/62966511/ provided by the user 'julemand101' ( https://stackoverflow.com/u/1953515/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Dart Type Errors: Fixing the _InternalLinkedHashMap<String, dynamic> Issue in Flutter

If you're diving into Flutter and interacting with Firestore, you might encounter a particularly frustrating error: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'TodoModel' in type cast. This is a common issue for newcomers, and understanding how to resolve it is crucial for your development. Let’s break down the problem and provide you with solutions step by step.

Understanding the Problem

The error typically happens when you're trying to convert a map that represents your data fetched from Firestore into a custom data model, like TodoModel. In this instance, your code attempts to cast a map directly into the TodoModel class without using the constructor, leading to the type error.

The Code Snippet Causing the Error

Consider the snippet below from the todo_provider.dart file, which highlights where the problem occurs:

[[See Video to Reveal this Text or Code Snippet]]

In this line, you're trying to add a map (data) directly to the _todoList, which is a list of TodoModel objects. Dart doesn't allow you to cast a map into a custom model directly. Instead, you need to construct a new instance of the model.

The Solution

To solve this issue, you will need to create a TodoModel object from the data fetched from Firestore instead of casting the map. Here’s how you can do that:

Updated Code Snippet

Instead of the casting line mentioned above, you should use the constructor of TodoModel to create an instance:

[[See Video to Reveal this Text or Code Snippet]]

Steps to Implement the Solution

Open your todo_provider.dart file.

Locate the fetchToDo function.

Replace the problematic line with the updated constructor call as shown above.

By doing this, you're effectively constructing a new TodoModel instance for each document fetched, which resolves the type casting issue.

Improving Your TodoModel Class

While you're at it, consider simplifying your TodoModel class. The current version has private variables and getter methods, but you can leverage Dart's features to make it cleaner. Here's a suggested improvement:

[[See Video to Reveal this Text or Code Snippet]]

Advantages of the Simplified Version

Readability: It’s easier to understand at a glance.

Conciseness: You eliminate the need for additional getter methods since you can access the properties directly.

Immutable Fields: Using final ensures that these fields cannot be changed once assigned, promoting better practices for data integrity.

Conclusion

Encountering type errors in Dart, particularly when working with Firestore, can be challenging for new Flutter developers. By carefully constructing your data models and understanding how to handle Dart types, you can enhance your coding efficiency and lower the chance of errors in your applications.

When you implement these changes, the error should disappear, allowing you to focus on building your Flutter app without interruptions. Happy coding!