即使我们不像其他 ViewController 生命周期方法那样在 viewcontroller 中覆盖它，是否也会调用 loadView？

Question

Does loadView get called even if we don't override it in view controller like the other ViewController lifecycle methods? Even if we don't override the ViewDidLoad method, we know this lifecycle method will get called internally by ios. Does the same thing happen for LoadView also? or does it gets called only when the view inside the VC is nil or when we explicitly override it?

Answer 1

It always gets called. From the documentation ,

The view controller calls this method when its view property is requested but is currently nil. This method loads or creates a view and assigns it to the view property.

If the view controller has an associated nib file, this method loads the view from the nib file. A view controller has an associated nib file if the nibName property returns a non-nil value, which occurs if the view controller was instantiated from a storyboard, if you explicitly assigned it a nib file using the init(nibName:bundle:) method, or if iOS finds a nib file in the app bundle with a name based on the view controller'€™s class name. If the view controller does not have an associated nib file, this method creates a plain UIView object instead.

...

You can override this method in order to create your views manually. If you choose to do so, assign the root view of your view hierarchy to the view property. The views you create should be unique instances and should not be shared with any other view controller object. Your custom implementation of this method should not call super.

It gets called even if you don't override it. Generally, you would only override it when you don't want to create a view controller from its nib. In this method, you would assign self.view some value (since view is loaded lazily). If you're not assigning some special subclass to your view property, you can usually get by by adding all your logic to viewDidLoad() .

Here's a sample implementation:

// Say you have some custom view you want use as your controller's view
class CustomView: UIView { ... } 

...
// In your view controller, you can set that custom instance to your view property.
override func loadView() {
    self.view = CustomView()
}

UITableViewController , for example, sets a UITableView as your view (presumably) in this method.

By default, the view is just a vanilla UIView. If that's all you need, there's no reason to call this method at all. viewDidLoad() is still a perfectly good place to do any additional initialization.

A couple of things to remember:

1. only assign to your view in loadView() . Don't invoke it (on the right-hand side; don't invoke its getter), because that can cause an infinite loop. If view is nil, loadView gets called to create it.
2. Don't call super.loadView() . This method is meant to assign a view to your view property. By calling super, you'd be doing this twice.

---

A little more info on the infinite loop trap you could fall into:

From UIViewController's view :

If you access this property and its value is currently nil, the view controller automatically calls the loadView() method and returns the resulting view.

view is created and assigned in loadView() when it is nil. If you do that within loadView itself, you will prompt loadView to be called within its own body.

Answer 2

Yes, it will still get called. You'll observe the same behavior as if you were to add this to your view controller.

override func loadView() {
  // Only call this to observe this is being called.
  // If you want to write your own implementation, you shouldn't call super.loadView().
  // Instead, create your own UIView instance and set self.view = yourView.
  super.loadView() 
}