【iOS】viewController的生命周期_瓯海剑_ios viewcontroller生命周期

网络 02-07 7076

viewController有自己的生命周期，其生命周期如下图：

?init - 初始化程序loadView - 在UIViewController对象的view被访问且为空的时候调用viewDidLoad - 视图加载完成后调用viewWillAppear -?UIViewController对象的视图即将加入窗口时调用viewDidAppear - UIViewController对象的视图已经加入窗口时调用viewWillDisappear - UIViewController对象的视图即将消失时调用viewDidDisappear - UIViewController对象的视图已经消失时调用didReceiveMemoryWarning - 出现内存警告dealloc -?视图被销毁，此次需要对你在init和viewDidLoad中创建的对象进行释放初始化

init?方法：

初始化UIViewController，执行关键数据初始化操作。不要在此操作view，view在loadView: 方法中才初始化。

加载视图

loadView?方法：

loadView:?方法是在UIViewController对象的view被访问且为空的时候调用，这个方法会加载或者创建一个view并将其赋值给view属性。在ViewController的生命周期中没有特殊情况只会被调用一次。你可以通过重写该方法来手动初始化views。在该方法的实现中，不能调用super。

viewDidLoad?方法：

view加载完成后调用。通常，我们对于各种初始化数据的载入，初始设定、修改约束、移除视图等很多操作都可以这个方法中实现。我们经常在此方法中添加一些控件和视图。

viewWillAppear?方法：

系统在载入所有的数据后，将会在屏幕上显示视图，这时会先调用这个方法，通常我们会在这个方法对即将显示的视图做进一步的设置。比如，设置设备不同方向时该如何显示；设置状态栏方向、设置视图显示样式等。当APP有多个视图时,上下级视图切换是也会调用这个方法,如果在调入视图时,需要对数据做更新,就只能在这个方法内实现。

viewDidAppear?方法：

UIViewController对象的视图已经加入窗口时调用。这时可以对正在显示的视图做设置。

viewWillDisAppear?方法：

UIViewController对象的视图即将消失、被覆盖或是隐藏时调用。

viewDidDisAppear?方法：

UIViewController对象的视图已经消失、被覆盖或是隐藏时调用。内存警告

didReceiveMemoryWarning ?方法：

在内存足够的情况下,app视图通常会一直保存在内存中,如果内存不够,会释放掉自己拥有的视图.系统只会释放内存,不会释放对象的所有权,通常我们需要在这里将不需要显示在内存中保留的对象释放它的所有权,置为nil。视图销毁

dealloc 方法：

销毁视图，释放资源。不要手动调用此方法，当引用计数值为0的时候，系统会自动调用此方法。代码案例

分为A和B两个视图。

A视图：

AViewController.h 文件：

#import <UIKit/UIKit.h> #import "BViewController.h" NS_ASSUME_NONNULL_BEGIN @interface AViewController : UIViewController @end NS_ASSUME_NONNULL_END

AViewController.m文件：

#import "AViewController.h" @interface AViewController () @end @implementation AViewController - (void) loadView { [super loadView]; NSLog(@"AViewController loadView"); } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. self.view.backgroundColor = [UIColor whiteColor]; UIButton* button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; button.frame = CGRectMake(100, 100, 100, 50); button.center = self.view.center; [button setTitle:@"按键" forState:UIControlStateNormal]; [button addTarget:self action:@selector(press:) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:button]; NSLog(@"AViewController viewDidLoad"); } - (void) viewWillAppear:(BOOL)animated { NSLog(@"AViewController viewWillAppear"); } - (void) viewDidAppear:(BOOL)animated { NSLog(@"AViewController viewDidAppear"); } - (void) viewWillDisappear:(BOOL)animated { NSLog(@"AViewController viewWillDisappear"); } - (void) viewDidDisappear:(BOOL)animated { NSLog(@"AViewController viewDidDisappear"); } - (void) didReceiveMemoryWarning { [super didReceiveMemoryWarning]; NSLog(@"AViewController didReceiveMemoryWarning"); } - (void) press:(UIButton*)sender { BViewController* bViewController = [[BViewController alloc] init]; bViewController.modalPresentationStyle = UIModalPresentationFullScreen; NSLog(@"A->B"); [self presentViewController:bViewController animated:YES completion:nil]; } @end

BViewController.h文件：

#import <UIKit/UIKit.h> NS_ASSUME_NONNULL_BEGIN @interface BViewController : UIViewController @end NS_ASSUME_NONNULL_END

BViewController.m文件：

#import "BViewController.h" @interface BViewController () @end @implementation BViewController - (void) loadView { [super loadView]; NSLog(@"BViewController loadView"); } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. self.view.backgroundColor = [UIColor yellowColor]; UIButton* button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; button.frame = CGRectMake(100, 100, 100, 50); button.center = self.view.center; [button setTitle:@"按键" forState:UIControlStateNormal]; [button addTarget:self action:@selector(press:) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:button]; NSLog(@"BViewController viewDidLoad"); } - (void) viewWillAppear:(BOOL)animated { NSLog(@"BViewController viewWillAppear"); } - (void) viewDidAppear:(BOOL)animated { NSLog(@"BViewController viewDidAppear"); } - (void) viewWillDisappear:(BOOL)animated { NSLog(@"BViewController viewWillDisappear"); } - (void) viewDidDisappear:(BOOL)animated { NSLog(@"BViewController viewDidDisappear"); } - (void) press:(UIButton*)sender { NSLog(@"B->A"); [self dismissViewControllerAnimated:YES completion:nil]; } @end

运行结果：

2022-09-18 18:34:13.549033+0800 ViewController[25007:24031989] AViewController loadView 2022-09-18 18:34:13.554447+0800 ViewController[25007:24031989] AViewController viewDidLoad 2022-09-18 18:34:13.563963+0800 ViewController[25007:24031989] AViewController viewWillAppear 2022-09-18 18:34:13.697255+0800 ViewController[25007:24031989] AViewController viewDidAppear 2022-09-18 18:34:16.421472+0800 ViewController[25007:24031989] A->B 2022-09-18 18:34:16.422527+0800 ViewController[25007:24031989] BViewController loadView 2022-09-18 18:34:16.423160+0800 ViewController[25007:24031989] BViewController viewDidLoad 2022-09-18 18:34:16.428482+0800 ViewController[25007:24031989] AViewController viewWillDisappear 2022-09-18 18:34:16.428732+0800 ViewController[25007:24031989] BViewController viewWillAppear 2022-09-18 18:34:16.933891+0800 ViewController[25007:24031989] BViewController viewDidAppear 2022-09-18 18:34:16.934169+0800 ViewController[25007:24031989] AViewController viewDidDisappear 2022-09-18 18:34:31.586055+0800 ViewController[25007:24031989] B->A 2022-09-18 18:34:31.587979+0800 ViewController[25007:24031989] BViewController viewWillDisappear 2022-09-18 18:34:31.588890+0800 ViewController[25007:24031989] AViewController viewWillAppear 2022-09-18 18:34:32.093543+0800 ViewController[25007:24031989] AViewController viewDidAppear 2022-09-18 18:34:32.093834+0800 ViewController[25007:24031989] BViewController viewDidDisappear

git:?https://github.com/sssxxd/ocstudy/tree/main/OC%20study/ViewController???????