view的操作在loadView还是viewDidLoad

本文包含对这篇文章的总结与思考loadView vs viewDidLoad FOR PROGRAMATIC UI SETUP

ViewController的生命周期中各方法执行流程如下：init—>loadView—>viewDidLoad—>viewWillAppear—>viewDidAppear—>viewWillDisappear—>viewDidDisappear—>viewWillUnload->viewDidUnload—>dealloc

loadView和viewDidLoad的区别就是，loadView时view还没有生成，viewDidLoad时，view已经生成了，loadView只会被调用一次，而viewDidLoad可能会被调用多次（View可能会被多次加载）

参考Apple文档中的说法:

If you prefer to create views programmatically, instead of using a storyboard, you do so by overriding your view controller’s loadView method. Your implementation of this method should do the following:

1. Create a root view object. …

2. Create additional subviews and add them to the root view.

   For each view, you should:

   1. Create and initialize the view.
   2. Add the view to a parent view using the addSubview: method.

3. If you are using auto layout, assign sufficient constraints to each of the views you just created to control the position and size of your views. Otherwise, …

4. Assign the root view to the view property of your view controller.

UIViewController:

If you cannot define your views in a storyboard or a nib file, override the loadView method to manually instantiate a view hierarchy and assign it to the view property.
…
You can override [the loadView] 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.
…
If you want to perform any additional initialization of your views, do so in the viewDidLoad method.

对上述文档的总结：

• 如果使用了storyboard或者nib，对view的其他操作在 viewDidLoad里面进行，viewDidLoad对view进行只读操作

• 若使用代码创建view，则在loadView里面进行

• 在loadView中，使用自己的view覆盖原本view的时候(self.view = CustomView() ) ，不应该调用super.loadView()

• 当controller是继承自UIViewController的时候，上述总结生效，如果是继承自其他controller(eg:UITableViewController)，view的操作要放在viewDidLoad