iOS的UI控件是weak还是strong修饰

第一种情况直接weak修饰后初始化，编译器会提示警告：Assigning retained object to weak property; object will be released after assignment，赋值后会被释放

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, weak) UIView *bview;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    self.view.backgroundColor = [UIColor whiteColor];
    self.bview = [[UIView alloc] init];
    NSLog(@"%@",self.bview);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"点击屏幕后%@",self.bview);
}

@end

结果

2023-11-29 10:32:51.003871+0800 OCDemo[82234:2684446] (null)
2023-11-29 10:33:01.251990+0800 OCDemo[82234:2684446] 点击屏幕后(null)

第二种情况用weak修饰赋值

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, weak) UIView *bview;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    self.view.backgroundColor = [UIColor whiteColor];
    UIView *tempView = [[UIView alloc] init];
    self.bview = tempView;
    NSLog(@"%@",self.bview);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"点击屏幕后%@",self.bview);
}

2023-11-29 10:36:17.927977+0800 OCDemo[82441:2688402] <UIView: 0x7f81ac704240; frame = (0 0; 0 0); layer = <CALayer: 0x600000a78340>>
2023-11-29 10:36:30.112701+0800 OCDemo[82441:2688402] 点击屏幕后(null)

第三种情况用weak修饰赋值后添加到view上

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, weak) UIView *bview;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    self.view.backgroundColor = [UIColor whiteColor];
    UIView *tempView = [[UIView alloc] init];
    self.bview = tempView;
    [self.view addSubview:self.bview];
    NSLog(@"%@",self.bview);
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    NSLog(@"点击屏幕后%@",self.bview);
}

2023-11-29 10:38:46.851065+0800 OCDemo[82679:2691860] <UIView: 0x7faec2f0c010; frame = (0 0; 0 0); layer = <CALayer: 0x6000000ab800>>
2023-11-29 10:38:48.487691+0800 OCDemo[82679:2691860] 点击屏幕后<UIView: 0x7faec2f0c010; frame = (0 0; 0 0); layer = <CALayer: 0x6000000ab800>>

最后一种情况为啥不被释放呢，原因是当我们执行了addSubview:方法之后，后面的视图就会被放到这个subViews数组里，可以看到，这个数组使用copy修饰的，也就是说，这是强引用！正是这个原因，我们才能用weak来修饰一个控件。因此可以保持这个控件的引用计数不为0，就不会被释放掉了。

@property(nonatomic,readonly,copy) NSArray<__kindof UIView *> *subviews;

总结一下：一般情况用weak，strong都可以的，但是特殊的种情况如果创建一个view用weak修饰，没有add到其他view上，那这个view就没有和别的view有强引用关系，引用计数也没有+1，所以会被释放，反之换成strong修饰的话，它本身就引用计数+1了，不管有没有被add到其他view上都不会被释放，所以不想这么纠结就都用strong修饰吧

还有个问题解释一下，strong修饰本身引用计数+1，addSubView后又+1，虽然引用计数为2，但是当整个父视图被销毁的时候，这两个引用计数都会变成0，所以不会造成内存泄漏。