Скачать или смотреть How to Resolve Cannot Fetch Data from Firebase Database in Flutter

Learn how to fix the `class bool has no instance method [] receiver null tried calling [] ok` error when accessing Firebase data in Flutter.
---
This video is based on the question https://stackoverflow.com/q/68921251/ asked by the user 'Jack' ( https://stackoverflow.com/u/16327298/ ) and on the answer https://stackoverflow.com/a/68924813/ provided by the user 'Frank van Puffelen' ( https://stackoverflow.com/u/209103/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: cannot fetch data from Firebase database

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Solving the Cannot Fetch Data from Firebase Database Issue in Flutter

If you've been working with Flutter and Firebase and encountered the frustrating error, class bool has no instance method [] receiver null tried calling [] ok, you are not alone. This issue often arises when developers attempt to fetch data from their Firebase database but face unexpected obstacles. In this guide, we’ll explore the cause of this error and provide a practical solution.

Understanding the Problem

The error you're encountering typically occurs when you try to access a field in the Firebase data structure that does not exist within the specified node. In your case, you're using a FirebaseAnimatedList to display user data based on their unique ID. Here’s a quick summary of the critical aspects at play:

Firebase Structure: You have a node structure like the following:

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

FirebaseAnimatedList: This widget is designed to show a list based on a Firebase query. However, if you're pointing to a specific user ID, it can be misleading.

The Root Cause

When you specify the user's UID in the query parameter of FirebaseAnimatedList, it results in retrieving multiple child nodes. For each snapshot that you retrieve, there are two properties: activity and ok. Here's what happens:

The itemBuilder gets called for each child node. In this case, it will be called twice because there are two properties: activity: true and ok: "ok".

When you try to access snapshot.value["ok"], it fails for the activity node, leading to the error you see.

This indicates that using FirebaseAnimatedList to show a singular user's data is not the right approach.

Solution: Using FutureBuilder

The right way to display data for a specific user without encountering errors is to use a FutureBuilder. This widget allows you to handle asynchronous data more effectively. Let’s breakdown how to implement it:

Step-by-Step Implementation

Replace FirebaseAnimatedList with FutureBuilder: Here’s how your code will look when using FutureBuilder:

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

Key Considerations

Error Handling: Make sure to check for errors and handle scenarios where the document doesn’t exist, ensuring a better user experience.

Loading State: Display appropriate loading messages while data is being fetched from Firebase, which improves the app's responsiveness.

Conclusion

To sum it up, the error class bool has no instance method [] receiver null tried calling [] ok arises due to the misuse of FirebaseAnimatedList for displaying individual user data. By switching to a FutureBuilder, you can efficiently fetch and display data without running into errors. Now you can enhance your Flutter app, making it more robust and user-friendly while working with Firebase data!

With these solutions and tips, you should be well on your way to resolving issues related to fetching data in your Flutter application.