Скачать или смотреть How to Effectively Show Data from a Class in Flutter

Learn how to display data in Flutter by maintaining a stable class instance to avoid common pitfalls.
---
This video is based on the question https://stackoverflow.com/q/68063347/ asked by the user 'rameez khan' ( https://stackoverflow.com/u/12791644/ ) and on the answer https://stackoverflow.com/a/68063395/ provided by the user 'Rob Lyndon' ( https://stackoverflow.com/u/1002908/ ) 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: Flutter how to show data from class

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.
---
How to Effectively Show Data from a Class in Flutter

When working with Flutter, a common challenge developers face is displaying data stored in a separate class. If you have ever attempted to show data in your widgets only to find that nothing appears, you're not alone. This issue often arises from managing the state incorrectly, specifically when dealing with multiple instances of your data class.

In this guide, we'll explore a straightforward solution to ensure that data from your class is displayed correctly in your Flutter widgets. We will use the example of a Collection class containing several items. Let's dive in!

Understanding the Problem

You might have a Collection class defined as follows:

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

You add data to the _items list like this:

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

While this seems to print the correct values in the addData function, the issue arises when trying to display this data using a ListView.builder. Here’s how you might have structured it:

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

The core issue is that every time you instantiate Collection() in your builder, you're creating a new, empty instance of Collection. Therefore, _items is always empty, which is why nothing is displayed.

The Solution

To solve this problem, follow these steps:

1. Create a Single Instance of Collection

Instead of creating a new instance of Collection every time you need it, create a single instance and store it in a variable:

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

2. Utilize the Same Instance in Your Builder

Next, use this instance in your ListView.builder as shown below:

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

3. Adding Data to Your Collection

You can now add data to your collection instance as follows:

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

Benefits of Using a final Variable

Immutability: Using final ensures that your instance of Collection does not get reassigned elsewhere in your code, which helps prevent bugs.

Clarity: It makes the intent of your code clear that this is the sole instance being used throughout your widget.

Conclusion

Managing state in Flutter can be tricky, especially when you're working with data classes. By creating a single instance of your Collection class and using it consistently, you can effectively display data in your widgets. This approach not only simplifies your code but also makes it less error-prone.

Now you’re ready to show data from classes in Flutter confidently! Remember, understanding the importance of instance management is key to overcoming many challenges in your Flutter development journey.

Happy coding!