How to Detect if SliverAppBar is Pinned in Flutter

Описание: Learn how to detect when a `SliverAppBar` is pinned in Flutter and dynamically change its header widget based on its scroll state.
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This video is based on the question https://stackoverflow.com/q/63949857/ asked by the user 'Janaka' ( https://stackoverflow.com/u/319343/ ) and on the answer https://stackoverflow.com/a/63950861/ provided by the user 'amugofjava' ( https://stackoverflow.com/u/4018724/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Detect if SliverAppBar is Pinned in Flutter

Working with SliverAppBar in Flutter can bring great UI flexibility to your application. However, many developers face a common challenge: how to seamlessly detect whether the SliverAppBar is pinned or not and to reflect that in the user interface. In this post, we will walk through the steps to effectively manage the pinned state of a SliverAppBar and display dynamic content accordingly.

Understanding the Challenge

When you scroll up, the SliverAppBar can either collapse and become pinned or stay in its expanded state. Many developers want to create a dynamic experience where the appearance of the app bar changes based on its pinned status. For instance, you may want to display one widget when the app bar is fully expanded and a different widget when it is pinned.

Key Question

How can we detect when the SliverAppBar is fully scrolled up and implement this dynamic behavior in our Flutter application?

Solution Overview

To effectively detect the pinned state of the SliverAppBar, we need to implement the following steps:

Use a Stateful Widget: This allows us to manage the state changes in our application when the SliverAppBar scrolls.

Implement a Scroll Controller: This controller will help us listen to the scrolling events and determine when the app bar has transitioned from expanded to pinned.

Step-by-Step Implementation

Step 1: Create a Stateful Widget

Begin by defining a StatefulWidget which will manage the state of the pinned header. Here’s a basic structure:

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

Step 2: Set Up the CustomScrollView

Next, implement the CustomScrollView, incorporating the SliverAppBar and attach the scroll controller:

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

Conclusion

By utilizing a Stateful Widget alongside a Scroll Controller, you can effectively detect when your SliverAppBar is pinned or not. This enables you to dynamically update the header content based on the scrolling behavior, providing a more interactive and engaging user experience.

With this implementation, you now have a working method to toggle between different widgets or states in your Flutter app, depending on the position of the SliverAppBar. Experiment with this and take your UI to the next level!