ViewController启动加载过程

 ViewController加载过程（ShowViewCycle是ViewController.view的subView）：

1. -[ViewController initWithNibName:bundle:] [Line 82] nibNameOrNil:(null), nibBundleOrNil:(null)

　　ViewController初始化方法: 

　　　　参数nibBundleOrNil：指定nib文件搜索的bundle，默认位mainBundle

　　　　参数nibNameOrNil：指定nib文件的名称，如果不指定，则先搜索View.nib，再搜索 ViewController.nib

2. -[ViewController loadView] [Line 100] 

　　在self.view==nil的条件下调用 

　　2.1 -[ViewController willMoveToParentViewController:] [Line 363] 

　　2.2 -[ShowViewCycle initWithFrame:] [Line 49] 

　　2.3 -[ShowViewCycle setNeedsDisplay] [Line 259] 

　　　　ShowViewCycle的属性改变都会触发setNeedsDisplay

　　2.4 -[ShowViewCycle setNeedsDisplay] [Line 259] 

　　2.5 -[ShowViewCycle setNeedsDisplay] [Line 259] 

　　2.6 -[ShowViewCycle willMoveToSuperview:] [Line 174] 

　　2.7 -[ShowViewCycle didMoveToSuperview] [Line 181] 

　　2.8 -[ShowViewCycle setTranslatesAutoresizingMaskIntoConstraints:] 

　　　　mas_makeConstraints主动触发

　　2.9 -[ShowViewCycle isDescendantOfView:] [Line 200]

　　　　addConstraint，会触发该判定，判定一个view是否是另一个view的subview

　　2.10-[ShowViewCycle isDescendantOfView:] [Line 200] 

　　2.11-[ShowViewCycle isDescendantOfView:] [Line 200] 

　　2.12-[ShowViewCycle isDescendantOfView:] [Line 200] 

3. -[ViewController viewDidLoad] [Line 107] 

　　3.1 -[ViewController shouldAutomaticallyForwardAppearanceMethods] [Line 336] 

　　返回值如果是NO，子类必须重写- viewWillAppear: -viewDidAppear: -viewWillDisappear: -viewDidDisappear: -willRotateToInterfaceOrientation:duration:  -willAnimateRotationToInterfaceOrientation:duration: -didRotateFromInterfaceOrientation:方法

4. -[ViewController viewWillAppear:] [Line 159] 

　　4.1 -[ViewController beginAppearanceTransition:animated:] [Line 298] 

　　4.2 -[ViewController shouldAutomaticallyForwardAppearanceMethods] [Line 336] 

　　4.3 -[ShowViewCycle willMoveToWindow:] [Line 188] 

　　4.4 -[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.5 -[ShowViewCycle needsUpdateConstraints] [Line 375] 

　　4.6 -[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.7 -[ShowViewCycle isDescendantOfView:] 

　　4.8 -[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.9 -[ShowViewCycle isDescendantOfView:] [Line 200] 

　　4.10-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.11-[ShowViewCycle isDescendantOfView:] [Line 200] 

　　4.12-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.13-[ShowViewCycle isDescendantOfView:] [Line 200] 

　　4.14-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.15-[ShowViewCycle didMoveToWindow] [Line 195] 

　　4.16-[ViewController viewWillLayoutSubviews] [Line 188] 

　　4.17-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.18-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.19-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.20-[ShowViewCycle intrinsicContentSize] [Line 451] 

　　　　　　内在内容的大小

　　4.21-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.22-[ShowViewCycle updateConstraints] [Line 370] 　　

　　4.23-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.24-[ShowViewCycle alignmentRectInsets] [Line 434] 

　　4.25-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.26-[ShowViewCycle alignmentRectInsets] [Line 434] 　　

　　4.27-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.28-[ShowViewCycle alignmentRectInsets] [Line 434] 

　　4.29-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 　　

　　4.30-[ShowViewCycle alignmentRectInsets] [Line 434] 

　　4.31-[ViewController updateViewConstraints] [Line 387] 

　　4.32-[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　4.33-[ShowViewCycle alignmentRectInsets] [Line 434] 

　　4.34-[ViewController viewDidLayoutSubviews] [Line 196] 

　　4.35-[ShowViewCycle layoutSubviews] [Line 231] 

　　4.36-[ShowViewCycle drawRect:] [Line 252] 

　　4.37-[ViewController shouldAutomaticallyForwardAppearanceMethods] [Line 336] 

5. -[ViewController viewDidAppear:] [Line 166] 

　　5.1 -[ViewController didMoveToParentViewController:] [Line 370] 

　　5.2 -[ViewController viewWillLayoutSubviews] [Line 188] 

　　5.3 -[ViewController updateViewConstraints] [Line 387] 

　　5.4 -[ShowViewCycle translatesAutoresizingMaskIntoConstraints] [Line 393] 

　　5.5 -[ShowViewCycle alignmentRectInsets] [Line 434] 

　　5.6 -[ViewController viewDidLayoutSubviews] [Line 196]