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[操作系统]你真的了解UIViewController生命周期吗?


一:首先了解一下生命周期图

 

二:UIViewController 生命周期介绍

1.通过alloc init 分配内存,初始化controller.

2.loadView
loadView方法默认实现[super loadView]
如果在初始化controller时指定了xib文件名,就会根据传入的xib文件名加载对应的xib文件,如果没传xib文件名,默认会加载跟controller同名的xib文件,如果没找到相关联的xib文件,就会创建一个空白的UIView,然后赋給controller的view

3.viewDidLoad
当loadView创建完view之后,此时view已经完成加载了,会调用viewDidLoad方法;一般我会在这里做界面上的初始化操作,比如添加按钮,子视图,等等.

4.viewWillAppear

当view在load完之后,将要显示在屏幕之前会调用这个方法

在重写这些方法时候最好先调用一下系统的方法之后在做操作。

5.viewDidAppear
当view已经在屏幕上显示出来之后,会调用这个方法

 

当一个视图被移除屏幕并且销毁的时候

 

6.viewWillDisappear
当视图将要从屏幕上移除时候调用

7.viewDidDisappear
当视图已经从屏幕上移除时候调用

8.dealloc
view被销毁时候调用,如果是手动管理内存的话,需要释放掉之前在init和viewDidLoad中分配的内存(类似alloc,new,copy);dealloc方法不能由我们主动调用,必须等引用计数为0时候由系统调用.

注意:viewDidUnload 在6.0之后已经废弃了。简单来说,对于iOS6,你不需要做任何以前viewDidUnload的事情,更不需要把以前viewDidUnload的代码移动到 didReceiveMemoryWarning方法中

三:UIViewController 生命周期实例

首先创建一个 ViewController,并这个页面上放一个button push到下一个页面;查看它的生命周期执行顺序;

ViewController代码:

 - (void)loadView {[super loadView];NSLog(@"%@------%s",[self class], __FUNCTION__);}- (void)viewDidLoad {[super viewDidLoad];// Do any additional setup after loading the view, typically from a nib.NSLog(@"%@------%s",[self class], __FUNCTION__);self.view.backgroundColor = [UIColor redColor];self.navigationItem.leftBarButtonItem =  [[UIBarButtonItem alloc]  initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self action:@selector(barClick:)];}- (void)viewWillAppear:(BOOL)animated {[super viewWillAppear:animated];NSLog(@"%@------%s",[self class], __FUNCTION__); } - (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; NSLog(@"%@------%s",[self class], __FUNCTION__); } - (void)viewWillDisappear:(BOOL)animated { [super viewWillDisappear:animated]; NSLog(@"%@------%s",[self class], __FUNCTION__); } - (void)viewDidDisappear:(BOOL)animated { [super viewDidDisappear:animated]; NSLog(@"%@------%s",[self class], __FUNCTION__); }  #pragma mark - buttonClick - (void)barClick:(UIBarButtonItem *)button { FirstViewController *VC = [[FirstViewController  alloc] init]; [self.navigationController  pushViewController:VC animated:YES]; }

第二个控制器FirstViewController 代码:

- (void)loadView {  [super loadView];  NSLog(@"%@------%s",[self class], __FUNCTION__);  }  - (void)viewDidLoad {  [super viewDidLoad];  // Do any additional setup after loading the view, typically from a nib.NSLog(@"%@------%s",[self class], __FUNCTION__);self.view.backgroundColor = [UIColor greenColor]; }// 视图将要出现时就会调用- (void)viewWillAppear:(BOOL)animated {[super viewWillAppear:animated];NSLog(@"%@------%s",[self class], __FUNCTION__);}// 视图完全出现时就会调用- (void)viewDidAppear:(BOOL)animated {[super viewDidAppear:animated];NSLog(@"%@------%s",[self class], __FUNCTION__);}// 视图将要消失会调用- (void)viewWillDisappear:(BOOL)animated {[super viewWillDisappear:animated];NSLog(@"%@------%s",[self class], __FUNCTION__);}// 视图完全消失会调用- (void)viewDidDisappear:(BOOL)animated {[super viewDidDisappear:animated];NSLog(@"%@------%s",[self class], __FUNCTION__);}

在ViewController页面中有一个button 点击button可以push到FirstViewController 由程序运行结果可知: 当刚运行程序时按顺序依次执行:

1. loadView2. viewDidLoad3. viewWillAppear4. viewDidAppear5. viewWillDisappear6. FirstViewController loadView7. FirstViewController viewDidLoad8. FirstViewController viewWillAppear9. viewController viewDidDisappear10. FirstViewController viewDidappear

当再一次点击左上角的返回键时 从FirstViewController跳转到viewController 由程序的运行结果可知 程序的运行顺序为;

1. loadView2. viewDidLoad3. viewWillAppear4. viewDidAppear5. viewWillDisappear6. FirstViewController loadView7. FirstViewController viewDidLoad8. FirstViewController viewWillAppear9. viewController viewDidDisappear10. FirstViewController viewDidappear11. FirstViewController viewWillDisappear12. viewController viewWillAppear13. FirstViewController viewWillDisappear14. viewController viewDidAppear

从程序的执行顺序可以看出来每个viewController只执行一次loadView和viewDidLoad