How to Change Pages with BottomNavigationBar in Flutter Without Errors

Описание: Learn how to effectively use `BottomNavigationBar` in Flutter to switch between pages without encountering the "setState() or markNeedsBuild() called during build." error.
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This video is based on the question https://stackoverflow.com/q/74323719/ asked by the user 'Foxify52' ( https://stackoverflow.com/u/20421666/ ) and on the answer https://stackoverflow.com/a/74325757/ provided by the user 'Sahil Sonawane' ( https://stackoverflow.com/u/15589902/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Navigating Between Pages with BottomNavigationBar in Flutter

When developing Flutter applications, you might find yourself needing to switch between different views or pages. A common way to achieve this is through the BottomNavigationBar. However, newcomers often encounter issues, such as the infamous "FlutterError setState() or markNeedsBuild() called during build." error. In this guide, we will explore how to implement a BottomNavigationBar effectively and solve switching pages without errors.

Understanding the Problem

The main issue arises when trying to switch between pages in Flutter while maintaining state management properly. If we call a method like Navigator.push() during the widget-building process, it can lead to complications and errors. Specifically, trying to manage navigation and state updates simultaneously can cause the Flutter framework to throw exceptions. Let's look at a solution that resolves this issue by ensuring the rendering process and state updates are handled in a way that avoids these pitfalls.

A Structured Solution

To implement a BottomNavigationBar correctly without facing runtime errors, follow these steps:

1. Setting Up Your Main Page Structure

We begin by constructing a stateful widget which will manage the selected index and the corresponding views to be displayed in the BottomNavigationBar. Here's how you can structure your main page:

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

2. Define Your Individual Pages

Create separate files or classes for each page that will be displayed when an icon in the BottomNavigationBar is tapped. For instance, your MessagePage might look like this:

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

3. Maintain Clear Navigation Logic

As shown in the solution, maintaining a _currentIndex variable helps track which page is currently selected. The switch statement allows the app to decide which widget to display based on that index.

4. Incorporating Aesthetic Customization

You can customize the BottomNavigationBar to suit your application’s aesthetic. Properties such as backgroundColor, selectedItemColor, and type can be easily modified to enhance user experience.

Conclusion

By correctly managing the state in a BottomNavigationBar and using the structure provided, you can smoothly switch between pages in a Flutter application without facing the notorious setState error. Structuring your pages and state management well is key to developing intuitive and user-friendly interfaces. Happy coding!