ios控制器生存周期

• iOS中控制器的生命周期

　　一般我们在创建控制器的时候，有三种方法。

　　1.  直接通过代码创建

　　2.  通过storyboard创建

　　3.  通过Xib，在创建控制器的时候传入一个Xib文件作为这个控制器的view。

• 直接通过代码创建

　　通过代码创建这种凡是，我们打印调用顺序可以发现

　　对应的代码调用顺序就是  loadView -> viewDidLoad -> viewWillAppear -> viewWillLayoutSubviews -> viewDidLayoutSubviews -> viewDidAppear

// 1.
- (void)loadView; // This is where subclasses should create their custom view
hierarchy if they aren‘t using a nib. Should never be called directly.

// 2.
- (void)viewDidLoad; // Called after the view has been loaded. For view controllers created in code, this is after -loadView. For view controllers unarchived from a nib, this is after the view is set.

// 3.
- (void)viewWillAppear:(BOOL)animated;    // Called when the view is about to made visible. Default does nothing

// 4.
- (void)viewWillLayoutSubviews NS_AVAILABLE_IOS(5_0);
// Called just after the view controller‘s view‘s layoutSubviews method is invoked. Subclasses can implement as necessary. The default is a nop.

// 5.
- (void)viewDidLayoutSubviews NS_AVAILABLE_IOS(5_0);

　　控制器创建之后，弹出另一个控制器(当前控制器消失)，执行的代码顺序 viewWillDisappear -> viewWillLayoutSubviews -> viewDidLayoutSubviews -> viewDidDisappear

// 1.
- (void)viewWillDisappear:(BOOL)animated; // Called when the view is dismissed, covered or otherwise hidden. Default does nothing

// 2.
- (void)viewWillLayoutSubviews NS_AVAILABLE_IOS(5_0);
// Called just after the view controller‘s view‘s layoutSubviews method is invoked. Subclasses can implement as necessary. The default is a nop.

// 3.
- (void)viewDidLayoutSubviews NS_AVAILABLE_IOS(5_0);

// 4.
- (void)viewDidDisappear:(BOOL)animated;  // Called after the view was dismissed, covered or otherwise hidden. Default does nothing

• 通过storyboard创建控制器

UIStoryboard *storyBoard = [UIStoryboard storyboardWithName:NSStringFromClass([CViewController class]) bundle:nil];
CViewController *touch = [storyBoard instantiateViewControllerWithIdentifier:NSStringFromClass([CViewController class])];
[self presentViewController:touch animated:YES completion:nil];

　　为了方便，同时减少手误，这里重用ID我们使用类名

　　通过打印来观察

　　可以看到代码的调用顺序就是 awakeFromNib -> loadView -> viewWillAppear -> viewWillLayoutSubviews -> viewDidLayoutSubviews -> viewDidAppear

// 1.
- (void)awakeFromNib NS_REQUIRES_SUPER;

// 2.
- (void)loadView; // This is where subclasses should create their custom view hierarchy if they aren‘t using a nib. Should never be called directly.

// 3.
- (void)viewDidLoad; // Called after the view has been loaded. For view controllers created in code, this is after -loadView. For view controllers unarchived from a nib, this is after the view is set.

// 4.
- (void)viewWillAppear:(BOOL)animated;    // Called when the view is about to made visible. Default does nothing

// 5.
- (void)viewWillLayoutSubviews NS_AVAILABLE_IOS(5_0);
// 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 NS_AVAILABLE_IOS(5_0);

// 6.
- (void)viewDidAppear:(BOOL)animated;     // Called when the view has been fully transitioned onto the screen. Default does nothing

　　这里需要注意的是，我们是控制器通过storyboard来加载，那么是根据storyboard的描述创建view。

• 通过XIB来创建加载控制器

　　首先创建一个XIB，快捷键 command + N 来创建。

　　创建后XIB之后我们还需要设置文件

这里设置为我们创建的控制器

　　所有需要的已经设置好，这时候我们可以来码代码了。

DViewController *touch = [[DViewController alloc] initWithNibName:NSStringFromClass([DViewController class]) bundle:nil];
[self presentViewController:touch animated:YES completion:nil];

　　下面我们来观察控制器的生命周期

　　代码层面上就是

// 1.
- (void)loadView; // This is where subclasses should create their custom view hierarchy if they aren‘t using a nib. Should never be called directly.

// 2.
- (void)viewDidLoad; // Called after the view has been loaded. For view controllers created in code, this is after -loadView. For view controllers unarchived from a nib, this is after the view is set.

// 3.
- (void)viewWillAppear:(BOOL)animated;    // Called when the view is about to made visible. Default does nothing

// 4.可能会多次调用
- (void)viewWillLayoutSubviews NS_AVAILABLE_IOS(5_0);
// 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 NS_AVAILABLE_IOS(5_0);

// 5.
- (void)viewDidAppear:(BOOL)animated;     // Called when the view has been fully transitioned onto the screen. Default does nothing

　　说明：

　　加载XIB的时候，我们同样可以不指定XIB名称，这样loadView 就会最终加载与控制器同名的 XIB （命名规范很重要啊）

DViewController *touch = [[DViewController alloc] init];
[self presentViewController:touch animated:YES completion:nil];

　　同时，如果我们删掉 DViewController.xib ,同时创建一个 DView.xib 当我们用以上不指定xib名称，同样是可以加载出来的（命名规范很重要）。

　　我们可以知道，加载xib的过程是，如果指定名称，那么加载指定名称的xib，如果没有指定名称就会加载和控制器同名的xib，如果没有就会找去控制器名相同但是没有 controller 的xib来加载。

• A present B控制器再返回，两个控制器的生命周期

　　1. 创建A控制器

　　流程：

A:loadView
A:viewDidLoad
A:viewWillAppear
A:viewWillLayout...
A:viewDidAppear

　　2. A present 到B控制器

　　流程：

A:loadView
A:viewDidLoad
A:viewWillAppear
A:viewWillLayout...    // 可能多次调用
A:viewDidAppear

-------------- Present B控制器 --------------

B:loadView
B:viewDidLoad

A:viewWillDisappear

B:viewWillAppear
B:viewLayout....   // 可能多次调用

A;viewLayout...   // 可能多次调用

B:viewDidAppear   // 多次调用，会跟下面的调用顺序可能会有些调换

A:viewDidDisappear