Initializing View Controllers 通过代码或者storyBoard



1. Initializing a View Controller

//   初始化一个视图控制器时 系统只会默认初始化它需要的组建，这样有利于内存的利用，(有点像最小系统，如果还需要其他组建，可以通过后续的添加及分配内存
When a view controller is first instantiated, it creates or loads objects it needs through its lifetime. It should
not create its view hierarchy or objects associated with displaying content. It should focus on data objects and
objects needed to implement its critical behaviors.

// 从StoryBoard上加载视图控制器

2.Initializing a View Controller Loaded from a Storyboard

// 通过StoryBoard设置的属性会序列化地放在一个压缩文件中，当view controller初始化时，archive会加载进内存，通过view controller’s initWithCoder: method
When you create a view controller in a storyboard,the attributes you configure in Interface Builder are serialized
into an archive.Later,when the view controller is instantiated,this archive is loaded into memory and processed.
The result is a set of objects whose attributes match those you set in Interface Builder. The archive is loaded by calling the view controller’s initWithCoder: method. Then, the awakeFromNib method is called on any
object that implements that method. You use this method to perform any configuration steps that require
other objects to already be instantiated.

3. Initializing View Controllers Programmatically
If a view controller allocates its resources programmatically,create a custom initialization method that is specific
to your view controller. This method should call the super class’s init method and then perform any class
specific initialization.
In general, do not write complex initialization methods. Instead, implement a simple initialization method and
then provide properties for clients of your view controller to configure its behaviors.

4. A View Controller Instantiates Its View Hierarchy When Its View is Accessed

// 通过调用loadView来加载View (可视化的视图)
Whenever some part of your app asks the view controller for its view object and that object is not currently in
memory, the view controller loads the view hierarchy into memory and stores it in its view property for future
reference. The steps that occur during the load cycle are:
1. The view controller calls its loadView method. The default implementation of the loadView method
does one of two things:

// 通过storyBoard来加载视图
 ● If the view controller is associated with a storyboard, it loads the views from the storyboard.

// 不是通过storyBoard 那么一个empty UIView对象会赋值给控制器的view Property
 ● If the view controller is not associated with a storyboard, an empty UIView object is created and
assigned to the view property.

// loadView 之后会调用 viewDidLoad 来完成load-time tasks
2. The view controller calls its viewDidLoad method,which enables your subclass to perform any additional
load-time tasks.