Fixing State Disappearance When Using emit in Flutter with Bloc

Описание: Learn how to maintain state in your Flutter app while using Bloc by understanding the principles of state management and how to fix issues when handling emit calls.
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This video is based on the question https://stackoverflow.com/q/74584767/ asked by the user 'newbiras' ( https://stackoverflow.com/u/20598947/ ) and on the answer https://stackoverflow.com/a/74586306/ provided by the user 'Hydra' ( https://stackoverflow.com/u/18299640/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Fix the Absence of State When Adding Another Emit in Flutter/Bloc

As a Flutter newbie trying to navigate the complexities of state management with Bloc, you may have encountered situations where your state appears to disappear after an emit call. This common problem particularly occurs during transitions to states like WaitingAuth, which represent a loading screen while awaiting an API response. Let's delve into the root cause of this issue and see how you can effectively resolve it.

Understanding the Problem

When you issue a command like emit(const WaitingAuth()), you may notice that the existing state values are lost. This is because you're not passing any parameters to the superclass (AuthState), resulting in all properties of the new state being set to null. Here’s the key part of the issue: the WaitingAuth constructor you defined does not carry over the current state values.

Here’s a quick summary of what's happening:

Your current state is overridden by a new state instance (WaitingAuth) that has no values initialized.

Consequently, all values, such as email, password, and other user information, turn to null when emitted.

Solution: Preserve the Current State

To resolve the disappearance of state during an emit transition, you need to preserve the current state before initiating the WaitingAuth emit. Here’s how you can fix it:

Step 1: Capture the Current State

Before emitting WaitingAuth, store the current state into a variable:

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

Step 2: Use Captured State for API Call

Utilize the stored state to make your API request. This will ensure you still have access to the necessary information such as email and password:

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

Summary

By capturing the current state before emitting WaitingAuth, you ensure that the required data remains intact throughout the API call. This not only keeps the values accessible but also allows for smoother user experiences while managing app states.

In summary:

Always pass along critical data when transitioning to different states in your Bloc architecture.

Use a variable to store the current state, to reduce bugs related to value loss and improve your application flow.

This approach provides a quick fix to a common state management problem in Flutter applications using Bloc, allowing you to build more reliable user experiences. Whether you're a beginner or an expert, fine-tuning how you manage and transmit your state is essential for a robust application architecture in Flutter.