Solving Core Data Refresh Issues with SwiftUI for Real-Time Shape Redrawing

Learn how to effectively use Core Data in SwiftUI to ensure that your custom shapes redraw in real-time during user interactions.
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Understanding Core Data Refresh Issues in SwiftUI

If you're working with SwiftUI and Core Data, you might face some issues with real-time updates—especially when you want to see live changes as you manipulate data, like moving points in a custom shape. This article will delve into a specific problem where Core Data does not trigger immediate refresh upon dragging points but works fine with simple types like CGPoint. We'll break down the solution to help you achieve the desired effect.

The Problem

Consider a scenario where you have a custom shape that users can interact with by moving points around. With a simple array of CGPoint, everything updates live and seemingly without issues. However, switching to a Core Data entity that represents points shows a different behavior. Specifically, when you drag a point, the shape doesn’t redraw immediately. It only updates after you interact with it again (e.g., double-tapping to add another point). This poses the question: Why does this happen?

The primary reason lies in how data binding and state management work in SwiftUI when using Core Data in contrast to simple Swift types.

The Solution

To ensure that your shape redraws in real-time as you drag points when leveraging Core Data, we need to utilize observable objects and explicitly notify SwiftUI of changes. Below, we’ll explore the updated code that effectively handles the issue.

Step 1: Create an Observable ViewModel

First, we create a PointsViewModel class that conforms to ObservableObject. This will allow us to publish changes when points are moved, ensuring that the UI refreshes appropriately.

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Step 2: Update the View to Use the ViewModel

Now we modified the RedrawEdgeTestCoreData view to leverage the PointsViewModel. It maintains the Core Data context alongside handling gestures for dragging and adding new points.

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Step 3: Run the Preview

The final step is ensuring this new implementation is reflected in previews and testing. You will want this view to be instantiated with the necessary environment.

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Conclusion

By employing an ObservableObject, we notify SwiftUI of changes to our data, allowing it to properly refresh the UI during user interactions. This approach seamlessly integrates Core Data with SwiftUI to enhance user experience by providing real-time updates.

Make sure to implement this in your projects where you require interactive shapes with Core Data!

If you have any questions or encounter issues, feel free to share in the comments below!