AutoLayout 的时机

AutoLayout by YongSir🇨🇳🇨🇳

• 视图布局相关

  // Called just before the view controller's view's layoutSubviews method is invoked. Subclasses can implement as necessary. The default is a nop.
  - (void)viewWillLayoutSubviews;
  
  // Called just after the view controller's view's layoutSubviews method is invoked. Subclasses can implement as necessary. The default is a nop.
  - (void)viewDidLayoutSubviews;

这两个在VC中方法，正如它的注释所述，会在VC的view的layoutSubviews被调用的之前和之后被调用，这也就是为什么，对一些添加到view的子视图布局之后，直到 viewDidLayoutSubviews才能得到正确的值！

• PS

  - (void)viewDidLoad
              |
  - (void)awakeFromNib
              |
  - (void)viewWillAppear:(BOOL)animated

可以看到viewDidLoad是最先的，它负责加载控制器，在它加载的过程中去查看view，如果从sb加载就去到awakeFromNib方法，然后再显示之类的，知道这些还不够，还需要知道：

111 viewDidload  -- self: <ZXMessgeCentreViewController: 0x1559a7280>, self.view: <UIView: 0x155f12cf0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x155be07a0>>

222 awake  -- self: <ZXMessgeCentreViewController: 0x1559a7280>, self.view: <UIView: 0x155f12cf0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x155be07a0>>

333 viewWillAppear -- self: <ZXMessgeCentreViewController: 0x1559a7280>, self.view: <UIView: 0x155f12cf0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x155be07a0>>

亲测Xcode7 beat 下从SB来的view已经布局，和viewDidLayoutSubviews中对比，这个方法进了2次，都是：
viewDidLayoutSubviews 中的view: <UIView: 0x12697d2d0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x126bd2450>>

• PPS

当然在实际使用时，最好能跟踪一下这几个方法，确定最好的时机