iOS 13 isKeyWindow always returns nil

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06-10-2024

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iOS 13 and the Mysterious Case of isKeyWindow Returning Nil

Have you ever encountered a situation where your iOS app's isKeyWindow property mysteriously returns nil in iOS 13? This seemingly innocuous issue can wreak havoc on your app's behavior, especially when dealing with UI updates or window-level interactions.

The Problem: In iOS 13, Apple introduced significant changes to the window management system, potentially leading to unexpected outcomes. The isKeyWindow property, historically used to determine the active window, can now return nil even when a window is clearly visible and interacting with the user.

Scenario: Let's say you're trying to update a UI element based on the isKeyWindow property of a specific window. Your code might look something like this:

if let window = UIApplication.shared.windows.first(where: { $0.isKeyWindow }) {
    // Update UI elements within the key window
} else {
    // Handle the case where no key window is found
}

The Issue: This code might work flawlessly on older iOS versions. However, in iOS 13 and above, the isKeyWindow check might fail, leading to the unexpected behavior of UI elements not updating as expected.

Why is this happening? The root cause lies in the subtle changes Apple introduced to the window management system in iOS 13. The concept of a "key window" has evolved to include more complex scenarios, including multi-window environments and the introduction of new UI paradigms like iPadOS.

Here's a breakdown of potential reasons why isKeyWindow might be returning nil:

• Multiple Windows: In iOS 13 and above, the system can accommodate multiple windows simultaneously. This means there might not be a single "key window" in the traditional sense.
• Window Hierarchy: Apple introduced a more hierarchical window management system, where windows can be "floating" or "attached" to other windows. This can lead to unexpected behavior when determining the active window.
• UI Paradigms: With the introduction of iPadOS and its multi-window support, the concept of a "key window" became more fluid. The active window can change dynamically depending on user interactions.

Solutions:

1. Utilize windows.first: In many scenarios, you can safely assume that the first window in the UIApplication.shared.windows array is the active window, even if isKeyWindow returns nil.
2. Check for isPresented: If you're dealing with a modal view controller, you can use the isPresented property to determine if the view controller is currently presented.
3. Focus on Window Hierarchy: Instead of relying solely on isKeyWindow, consider leveraging the window hierarchy. For example, you can use window.rootViewController to access the root view controller of a specific window.
4. Use a Dedicated Window Manager: For complex scenarios involving multiple windows and window transitions, it might be beneficial to implement a custom window manager to handle active window detection.

Remember: While isKeyWindow is still available in iOS 13 and above, it's crucial to understand its limitations and adapt your code to account for the new window management system.

Additional Resources:

• Apple Documentation: UIWindow
• Apple Developer Forums

By understanding the nuances of window management in iOS 13 and beyond, you can avoid the pitfalls of isKeyWindow returning nil and ensure your app continues to function smoothly across all iOS versions.