【iOS】—— ViewController生命周期

ViewController生命周期

首先来看下ViewController在运行过程中的函数介绍：

• loadView：加载view。这个方法中，要正式加载View了，控制器 view 是通过懒加载的方式进行加载的，即用到的时候再加载。在 view 加载过程中首先会调用 loadView 方法，在这个方法中主要完成一些关键 view 的初始化工作。
• viewWillAppear: 视图将要显示
• viewWillLayoutSubviews：控制器的view将要布局子控件
• viewDidLayoutSubviews： 控制器的view布局子控件完成
• viewDidAppear: 视图已经显示
• viewWillDisappear: 视图将要消失
• viewDidDisappear: 视图已经消失

过程图可看如下：

我们来看一个demo，设计思想为从第一个界面切换到第二个界面，再从第二个界面切换回第一个界面，全程当这些函数运行的时候打印出函数名：

第一个界面：

//
//  FirstViewController.m
//  ViewController生命周期
//
//  Created by 翟旭博 on 2022/9/16.
//

#import "FirstViewController.h"
#import "SecondViewController.h"
@interface FirstViewController ()

@end

@implementation FirstViewController

- (void)loadView {
    [super loadView];
    NSLog(@"loadView1");
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    NSLog(@"viewDidLoad1");
    
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [self.view addSubview:button];
    button.tintColor = [UIColor blackColor];
    button.frame = CGRectMake(100, 100, 100, 100);
    [button addTarget:self action:@selector(press) forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:@"go" forState:UIControlStateNormal];
    

}

- (void)press {
    NSLog(@"first back------------------------");
    SecondViewController *vc = [[SecondViewController alloc] init];
    vc.modalPresentationStyle = UIModalPresentationFullScreen;
    [self presentViewController:vc animated:YES completion:nil];
}

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    NSLog(@"viewWillLayoutSubviews1");
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    NSLog(@"viewDidLayoutSubviews1");
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"viewWillAppear1");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"viewDidAppear1");
}
- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"viewWillDisappear1");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"viewDidDisappear1");
}

- (void)dealloc {
    NSLog(@"dealloc1");
}

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第二个界面：

//
//  SecondViewController.m
//  ViewController生命周期
//
//  Created by 翟旭博 on 2022/9/16.
//

#import "SecondViewController.h"
#import "FirstViewController.h"
@interface SecondViewController ()

@end

@implementation SecondViewController

- (void)loadView {
    [super loadView];
    NSLog(@"loadView2");
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    NSLog(@"viewDidLoad2");
    
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [self.view addSubview:button];
    button.tintColor = [UIColor blackColor];
    button.frame = CGRectMake(100, 100, 100, 100);
    [button addTarget:self action:@selector(press) forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:@"back" forState:UIControlStateNormal];
    

}

- (void)press {
    NSLog(@"second back------------------------");
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    NSLog(@"viewWillLayoutSubviews2");
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    NSLog(@"viewDidLayoutSubviews2");
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"viewWillAppear2");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"viewDidAppear2");
}
- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"viewWillDisappear2");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"viewDidDisappear2");
}

- (void)dealloc {
    NSLog(@"dealloc2");
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

@end

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当app启动进入第一个界面：

此时输出结果：

app进入第二个界面：

此时输出结果：

app返回第一个界面：