Скачать или смотреть How to Change a Variable in a Custom Class Widget in Flutter

Learn how to modify a variable inside a custom class widget in `Flutter` and update its value effectively using constructors.
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This video is based on the question https://stackoverflow.com/q/65061709/ asked by the user 'Anan Saadi' ( https://stackoverflow.com/u/12771325/ ) and on the answer https://stackoverflow.com/a/65061754/ provided by the user 'Tugay' ( https://stackoverflow.com/u/11199298/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Changing a Variable in a Custom Class Widget in Flutter

Flutter is an amazing toolkit for building natively compiled applications for mobile, web, and desktop from a single codebase. A common scenario you might encounter while developing Flutter applications is the need to change properties of a custom widget. In this guide, we will explore how to change a variable in a custom class widget dynamically. This functionality is crucial for building responsive and interactive applications.

The Problem

You might find yourself in a situation where you need to adjust the value of a variable, such as color, within your custom class widget. The widget should be able to reflect this change dynamically. For example, consider a simple Flutter custom widget called Test, which you've defined as follows:

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In this example, the color variable isn't directly tied to any constructor, making it difficult to change its value from outside the widget. We'll discuss the solution to this problem in detail below.

The Solution

To change the variable inside your custom widget, you'll want to pass the new value to color via the widget's constructor. Let’s break it down step by step:

Step 1: Modify the Class Definition

You’ll need to create a constructor in the Test class that can accept a Color parameter. Here's how you can do that:

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Step 2: Access the Variable in the State Class

In the state class, there’s no need to have a separate color variable. Instead, you will access the color variable via the widget property in your _TestState class. Update the build method like this:

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Step 3: Use the Widget and Pass the Color

Now that your widget is ready to receive a color, you can instantiate it and pass the desired color value as follows:

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Example Usage

Here's an example of how you might use the Test widget in your main application:

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Key Takeaways

Passing values to widgets via constructors is a powerful way to manage state in Flutter.

Flutter’s widget framework is optimized for rebuilding, which makes it easy to reflect changes to the UI with new values.

By leveraging the constructor, we ensure that our widgets are both flexible and reusable.

Conclusion

In this guide, we explored how to change a variable in a custom class widget in Flutter by properly utilizing constructors to pass values. This pattern not only makes your widgets easier to manage but also enhances the reusability of your code. Happy coding!