ViewController学习笔记

The steps that occur during the load cycle are as follows:

1. Some part of your application asks for the view in the view controller’s view property.

2. If the view is not currently in memory, the view controller calls its loadView method.

3. The loadView method does one of the following:

   ● If you override this method, your implementation is responsible for creating all necessary views and assigning a non-nil value to the view property.

   ● If you do not override this method, the default implementation uses the nibName and nibBundle properties of the view controller to try to load the view from the specified nib file. If the specified nib file is not found, it looks for a nib file whose name matches the name of the view controller class and loads that file.

   ● If no nib file is available, the method creates an empty UIView object and assigns it to the view property.

4. The view controller calls its viewDidLoad method to perform any additional load-time tasks. 

 

The steps that occur during the unload cycle are as follows:

1. The application receives a low-memory warning from the system.

2. Each view controller calls its didReceiveMemoryWarning method:

   • ●  If you override this method, you should use it to release any custom data that your view controller object no longer needs. You should not use it to release your view controller’s view. You must call super at some point in your implementation to perform the default behavior.

   • ●  The default implementation releases the view only if it determines that it is safe to do so.

3. If the view controller releases its view, it calls its viewDidUnload method. You can override this method

   to perform any additional cleanup required for your views and view hierarchy.