How to Dynamically Update a SwiftUI View with a @ Bindable Value

Learn how to effectively use SwiftUI's `@ Bindable` properties to update your views dynamically. This guide covers structuring your code to calculate progress percentages using Core Data in SwiftUI.
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How to Dynamically Update a SwiftUI View with a @ Bindable Value

In SwiftUI, making your views responsive to changes in state can be a challenge, especially when working with data from external sources like Core Data. If you're trying to create a ProgressBar that dynamically updates based on user input and internal calculations, it’s essential to understand how to leverage SwiftUI's property wrappers effectively.

The Problem

You might find yourself struggling to structure your SwiftUI code because of the complexity surrounding property wrappers like @ Binding, @ Published, and @ State. For instance, when displaying progress percentages based on reminders saved in Core Data, you might encounter errors that prevent your views from updating as expected.

To better understand this issue, we'll walk through a common scenario where you wish to display the percentage progress of reminders that need to be completed, and highlight how to fix related issues.

Understanding the Structure

Here is a simplified outline of the components involved:

Model Class

You have a Reminder class saved in Core Data that includes methods to calculate progress:

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

Helper Class

Although you had a ReminderHelper class that intended to calculate the progress, we can simplify this. By adding a computed property directly within the Reminder model, we can avoid unnecessary complexity and errors.

SwiftUI View

In your ContentView, you need to present this data dynamically:

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

Progress Bar View

Your ProgressBar view can be structured as follows, using a simple Float instead of a binding since it doesn’t modify the state:

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

Key Takeaways

Avoid Unnecessary Complexity: Instead of using a separate class for calculations, leverage computed properties directly within your model.

Correct Usage of Types: Ensure that calculations in properties like percentageLeft are accurately typed to avoid runtime issues.

Understanding Views: Only use @ Binding when you need to propagate changes to a parent view. For static values, a simple variable suffices.

By implementing these changes, you should see dynamic updates in your ProgressBar as conditions change, aligning with what you initially expected.

This structured approach not only resolves the primary issue but also simplifies the overall architecture of your SwiftUI application.