If you're an iOS developer, you may have encountered the error message "Whose View is Not in the Window Hierarchy!" This error typically occurs when you try to access a view that is not currently visible on the screen. In this guide, we'll discuss what causes this error and provide a step-by-step solution to fix it.
What Causes the 'Whose View is Not in the Window Hierarchy!' Error?
This error occurs when you try to manipulate a view that is not currently visible on the screen. For example, if you try to update the text of a label that is not currently visible, you may encounter this error. This typically happens when you try to access a view in the viewDidLoad method of a view controller.
Step-by-Step Solution
Follow these steps to fix the "Whose View is Not in the Window Hierarchy!" error:
Move the code that is causing the error to the viewWillAppear or viewDidAppear methods of your view controller. These methods are called after the view is added to the view hierarchy and are a safer place to manipulate your views.
If you need to access a view in the viewDidLoad method, wrap your code in a DispatchQueue.main.async block. This will ensure that your code is executed on the main thread, which is required for all UI updates.
DispatchQueue.main.async {
// Your code here
}
- If you're still encountering the error, check that the view you're trying to manipulate is actually in the view hierarchy. You can do this by adding a breakpoint and inspecting the view hierarchy using Xcode's Debug View Hierarchy tool.
FAQ
Q1. Can I fix the error by simply moving my code to the viewWillAppear or viewDidAppear methods?
A1. Yes, moving your code to these methods is the recommended solution for this error.
Q2. Why do I need to use DispatchQueue.main.async to update my views?
A2. All UI updates must be executed on the main thread. Using DispatchQueue.main.async ensures that your code is executed on the main thread.
Q3. Can I use other methods to check if a view is in the view hierarchy?
A3. Yes, you can use the isDescendant method of UIView to check if a view is in the view hierarchy.
Q4. What other errors can occur when manipulating views in iOS?
A4. Other common errors include "Thread 1: Signal SIGABRT" and "EXC_BAD_ACCESS".
Q5. Are there any other best practices for manipulating views in iOS?
A5. Yes, it's best practice to keep your view manipulation code as simple as possible and avoid nesting views within views. This will make it easier to track down errors and improve the performance of your app.