10 Flutter BLoC Best Practices

BLoC is a great way to manage state in a Flutter app, but there are some best practices to follow to make sure things go smoothly.

Flutter BLoC (Business Logic Component) is a popular state management pattern used in mobile application development. It helps developers to separate the business logic from the UI layer, making the code more maintainable and easier to test.

However, it can be difficult to implement BLoC correctly. In this article, we will discuss 10 best practices for using Flutter BLoC to ensure that your application is well-structured and maintainable. We will also discuss how to avoid common pitfalls and ensure that your application is optimized for performance.

1. Use a single BLoC for each screen

Using a single BLoC for each screen helps to keep the code organized and easy to maintain. It also makes it easier to debug, since you can easily identify which part of the code is causing an issue. Additionally, using a single BLoC allows you to reuse the same logic across multiple screens, making your app more efficient. Finally, having a single BLoC per screen makes it easier to test, as you don’t have to worry about testing multiple BLoCs at once.

2. Use the provider package to expose your BLoCs

The provider package allows you to easily expose your BLoCs to the rest of your application, making them accessible from any widget in your app. This makes it easier for you to manage and update your BLoCs as needed.

The provider package also provides a way to inject dependencies into your widgets, which can be useful when dealing with complex applications that require multiple BLoCs. By using the provider package, you can ensure that all of your widgets have access to the same data and state, allowing for better code reuse and maintainability.

3. Always use Streams and never setState directly in the UI

When using Streams, you can easily separate the business logic from the UI. This makes it easier to test and debug your code since all of the business logic is in one place. It also allows for better scalability as you can add more features without having to rewrite existing code.

Additionally, when using Streams, you don’t have to worry about managing state directly in the UI. Instead, you can use a BLoC pattern which will handle the state management for you. This makes it much easier to maintain and update your app over time.

4. Don’t call sink.add from outside of the BLoC

When you call sink.add from outside of the BLoC, it can lead to unexpected behavior and bugs in your app. This is because when you call sink.add from outside of the BLoC, you are bypassing the logic that is contained within the BLoC itself. By doing this, you could be sending data into the BLoC that isn’t properly formatted or validated, which could cause errors down the line.

Therefore, it’s important to make sure that all calls to sink.add are made from within the BLoC itself. This ensures that all data sent into the BLoC is properly formatted and validated before being processed.

5. Create one event class per BLoC for all events

When using the BLoC pattern, it’s important to keep your code organized and easy to read. Having one event class per BLoC helps with this by keeping all of the events related to a particular BLoC in one place. This makes it easier for developers to find what they’re looking for when debugging or making changes.

It also allows you to easily add new events as needed without having to search through multiple classes. Additionally, if you need to make changes to an existing event, you can do so quickly and easily since all of the events are located in one place.

6. Create one state class per BLoC for all states

Having one state class per BLoC allows you to easily manage the states of your application. It also makes it easier for developers to understand and debug the code, as all the states are in one place. Additionally, having a single state class helps keep the code DRY (Don’t Repeat Yourself) by avoiding duplication of code.

Finally, using one state class per BLoC is more efficient than creating multiple classes for each state. This reduces the amount of memory used and improves performance.

7. Keep business logic out of the UI

The UI is responsible for displaying data and responding to user input, but it should not be responsible for making decisions about how the app behaves. That’s where business logic comes in. By keeping business logic out of the UI, you can ensure that your code is more maintainable and easier to test.

To do this, create a separate class or module for your business logic. This will allow you to keep your UI code clean and focused on what it does best: presenting data and responding to user input. It also makes it easier to reuse your business logic across multiple screens and apps.

8. Write tests for every part of your BLoC

Testing is essential for ensuring that your BLoC works as expected. It helps you catch bugs early on and makes sure that the code you write is reliable and maintainable. Writing tests also allows you to refactor your code with confidence, knowing that any changes won’t break existing functionality.

When writing tests for a Flutter BLoC, it’s important to test both the input and output streams of data. This means testing the events that are sent into the BLoC, as well as the states that are emitted from it. Additionally, you should also test the logic within the BLoC itself, such as verifying that certain actions result in the correct state being emitted.

9. Avoid using sinks inside streams

Sinks are used to send data into a stream, while streams are used to receive data from a sink. When you use sinks inside of streams, it can cause confusion and make the code more difficult to read and maintain. It also makes debugging harder because there is no clear source or destination for the data.

Instead, try using multiple streams that communicate with each other through transformers. This will help keep your code organized and easier to understand. Additionally, it will make debugging much simpler since you’ll be able to clearly see where the data is coming from and going to.

10. Do not expose the stream controllers

Exposing the stream controllers can lead to a lot of problems. For example, if someone were to call the add method on the controller directly, it could cause unexpected behavior in your app. It’s also possible that someone could accidentally close the stream, which would prevent any further events from being emitted.

By not exposing the stream controllers, you ensure that only the BLoC is able to control the streams and emit events. This helps keep your code clean and maintainable, as well as ensuring that all events are handled correctly.


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