Description

whose view is not in the window hierarchy ?

**Title: Resolving the “Whose View Is Not in the Window Hierarchy” Error in iOS Development**

Hello everyone,

If you’ve ever come across the frustrating error “Warning: Attempt to present on * whose view is not in the window hierarchy” in your iOS app development, you’re not alone. This error occurs when an attempt to present a view controller is made, but one of the controllers in the hierarchy is not yet attached to the window. Let’s break down this issue and look at solutions to fix it.

### Understanding the Error
The error typically occurs under the following circumstances:

1. **Controller Not in Hierarchy**: The view controller from which the modal is being presented is not currently part of the window’s view hierarchy.
2. **Controller Not the Top Controller**: The view controller trying to present another is not the topmost view controller in the navigation stack.
3. **Multiple Alerts**: Presenting an alert when another dialog or alert is already shown, without dismissing it first.

### Solutions and Workarounds

#### Solution 1: Pass the Correct ViewController
A common approach to prevent this error is to pass the currently active view controller as the presenting controller. This ensures that the view controller is in the view hierarchy when the modal presentation occurs. You can modify the presentation method as follows:

“`swift
func presentViewController(presentingController: UIViewController, animated: Bool, completion: (() -> Void)?) {
presentingController.present(self, animated: animated, completion: completion)
}
“`

Ensure when you make the call to present, you call it from a view controller that is within the app’s window’s hierarchy:

“`swift
let storyboard = UIStoryboard(name: “Main”, bundle: nil)
let viewController = storyboard.instantiateViewController(withIdentifier: “ViewControllerID”)
presentViewController(presentingController: self, animated: true, completion: nil)
“`

#### Solution 2: Use the Top Most Controller
To be more robust, you can create a helper method that always finds the topmost view controller and attempts to present from there:

“`swift
extension UIWindow {
var visibleViewController: UIViewController? {
return self.visibleViewController
}

var visibleViewController: UIViewController? {
if let rootViewController = rootViewController {
return UIWindow.getVisibleViewControllerFrom(vc: rootViewController)
}
return nil
}

class func getVisibleViewControllerFrom(vc: UIViewController) -> UIViewController? {
if var topController = vc.presentedViewController {
while let presentedViewController = topController.presentedViewController {
topController = presentedViewController
}
return topController
}
if let navigationController = vc as? UINavigationController {
return getVisibleViewControllerFrom(vc: navigationController.visibleViewController!)
}
return vc
}
}
“`

Then, before presenting, you would call `UIWindow.key?.visibleViewController` to ensure the view controller is visible before the presentation.

#### Solution 3: Delay the Presentation
Another way to handle this is by deferring the presentation until after the view controller has been loaded. Use `DispatchQueue.main.async` to defer the presentation:

“`swift
DispatchQueue.main.async {
self.present(yourViewController, animated: true, completion: nil)
}
“`

This forces the system to wait until all current operations are complete before attempting to present the new view controller.

### Additional Tips
– Always ensure that the view you’re trying to present isn’t already loaded and part of another context, such as being presented twice.
– Check that no modal screens are overlapping or inadvertently presented on other view controllers.
– Make sure your view controllers are not destroyed and re-instantiated while trying to present new views.

By understanding these solutions and adapting your approach, you can maintain a smooth flow without this error disrupting the user’s experience. If you find yourself still running into issues, examining your view transition logic and lifecycle methods might provide more clues.

That’s all for today. If you have any other iOS errors or questions, comment below. Until then, happy coding!

– [Your Blogging Name]