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【iOS】ViewController的生命周期

article 2024/9/23 5:28:49

【iOS】ViewController的生命周期

与ViewController生命周期有关的函数

Init
loadView()当需要展示view而view为nil时，ViewController会调用loadView方法。
viewDidLoad()类成员对象和变量的初始化都在这个方法里，在创建类后无论视图展现还是消失，这个方法只会在布局时调用一次
viewWillAppear():视图将要展现的时候调用
viewDidAppear():视图已经出现时调用
viewWillLayoutSubviews()用于处理视图布局的变化，通常在这里执行与布局相关的操作，在子视图重新布局之前调用
viewDidLayoutSubviews()用于处理视图布局的变化，在子视图重新布局之后调用
viewWillDisapper():视图即将消失时调用
viewDidDisapper():视图已经消失时调用
traitCollectionDidChange()视图控制器的特征集合发生变化时调用
didReceiveMemoryWarning()系统内存不足时调用

执行顺序

用一个简单的程序来展示一下这些函数的执行顺序，创建两个视图控制器并在两个视图控制器之间切换，在调用的函数中打印当前函数，以此来查看函数的调用情况。

AViewController:

#import "AViewController.h"
#import "BViewController.h"

@interface AViewController ()

@end

@implementation AViewController

- (void)viewDidLoad {
    
    UIColor *pinkColor = [UIColor colorWithRed:255/255.0 green:192/255.0 blue:203/255.0 alpha:1.0];
    UIColor *hotPinkColor = [UIColor colorWithRed:1.0 green:0.4117 blue:0.7059 alpha:1.0];
    
    [super viewDidLoad];
    self.view.backgroundColor = hotPinkColor;
    self.button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    self.button.frame = CGRectMake(137, 406, 120, 40);
    [self.view addSubview:self.button];
    [self.button setTitle:@"AGoToB" forState:UIControlStateNormal];
    [self.button setTitleColor:pinkColor forState:UIControlStateNormal];
    self.button.titleLabel.font = [UIFont systemFontOfSize:30];
    [self.button addTarget:self action:@selector(move) forControlEvents:UIControlEventTouchUpInside];
    NSLog(@"%s", __func__);
}

- (void)move {
    NSLog(@"A ------> B");
    BViewController* bViewController = [[BViewController alloc] init];
    bViewController.modalPresentationStyle = UIModalPresentationFullScreen;
    [self presentViewController:bViewController animated:YES completion:nil];
}

- (void)loadView {
    [super loadView];
    NSLog(@"%s", __func__);
}

- (void)viewWillAppear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewWillLayoutSubviews {
    NSLog(@"%s", __func__);
}

- (void)viewDidLayoutSubviews {
    NSLog(@"%s", __func__);
}

- (void)viewWillDisappear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewDidDisappear:(BOOL)animated {
    NSLog(@"%s", __func__);
}
@end

BViewController:

#import "BViewController.h"

@interface BViewController ()

@end

@implementation BViewController

- (void)viewDidLoad {
    
    UIColor *pinkColor = [UIColor colorWithRed:255/255.0 green:192/255.0 blue:203/255.0 alpha:1.0];
    UIColor *deepPinkColor = [UIColor colorWithRed:1.0 green:0.0784 blue:0.5765 alpha:1.0];
    
    [super viewDidLoad];
    self.view.backgroundColor = deepPinkColor;
    self.button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    self.button.frame = CGRectMake(117, 406, 160, 40);
    [self.button setTitle:@"BBackToA" forState:UIControlStateNormal];
    [self.view addSubview:self.button];
    [self.button setTitleColor:pinkColor forState:UIControlStateNormal];
    self.button.titleLabel.font = [UIFont systemFontOfSize:30];
    [self.button addTarget:self action:@selector(BBackToA) forControlEvents:UIControlEventTouchUpInside];
    NSLog(@"%s", __func__);
}

- (void)BBackToA {
    NSLog(@"B --------> A");
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (void)loadView {
    [super loadView];
    NSLog(@"%s", __func__);
}

- (void)viewWillAppear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewWillLayoutSubviews {
    NSLog(@"%s", __func__);
}

- (void)viewDidLayoutSubviews {
    NSLog(@"%s", __func__);
}

- (void)viewWillDisappear:(BOOL)animated {
    NSLog(@"%s", __func__);
}

- (void)viewDidDisappear:(BOOL)animated {
    NSLog(@"%s", __func__);
}
@end

呈现效果：

程序输出:

根据程序的输出我们总结出：

对于单个视图控制器，函数调用的顺序是：loadView -> viewDidLoad -> viewWillAppear -> viewWillLayoutSubviews -> viewDidLayoutSubviews -> viewDidAppear
对于两个视图控制器互相切换，被切换的视图控制器会先调用viewWillDisapper，直到切换出来的视图控制器调用viewDidAppear后，被切换的视图控制器才会调用viewDidDisapper。以上图为例：AviewController先调用viewWillDisapper，然后BviewController调用一系列函数，直到BviewController调用viewDidAppear后，AviewController才调用viewDidDisappear

另外，这里AviewController只调用过一次loadView，BviewController多次反复调用loadView，由此可知，在BviewController执行完dismiss后，内存就被释放掉了，而AviewController作为根视图控制器是一直没有被释放的

注意

这里loadview的函数中写上[super loadview]，这是因为当view为nil时，就会调用loadview方法。如果找不到view的话，程序就会一直调用loadview方法来寻找view。