iOS 修饰符strong和weak

举个栗子：

@interface TestViewController ()

@property (nonatomic,strong) UIButton *strongButton;
@property (nonatomic,weak) UIButton *weakButton;

@end

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.navigationController.navigationBar.translucent = NO;
    
    self.strongButton = [UIButton buttonWithType:UIButtonTypeCustom];
    self.strongButton.backgroundColor = [UIColor blackColor];
    [self.strongButton setTitle:@"强按钮" forState:UIControlStateNormal];
    [self.strongButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [self.strongButton addTarget:self action:@selector(strongButtonClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.strongButton];
    [self.strongButton mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(self.view);
        make.top.equalTo(@100);
        make.size.mas_equalTo(CGSizeMake(80, 30));
    }];
    
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    button.backgroundColor = [UIColor blackColor];
    [button setTitle:@"弱按钮" forState:UIControlStateNormal];
    [button setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [button addTarget:self action:@selector(weakButtonClick:) forControlEvents:UIControlEventTouchUpInside];
    self.weakButton = button;
    [self.view addSubview:self.weakButton];
    [self.weakButton mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(self.view);
        make.top.equalTo(@150);
        make.size.mas_equalTo(CGSizeMake(80, 30));
    }];
    
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.backgroundColor = [UIColor blackColor];
    [btn setTitle:@"测试按钮1" forState:UIControlStateNormal];
    [btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(button1Click:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];
    [btn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(self.view);
        make.top.equalTo(@200);
        make.size.mas_equalTo(CGSizeMake(80, 30));
    }];
    
    UIButton *btnn = [UIButton buttonWithType:UIButtonTypeCustom];
    btnn.backgroundColor = [UIColor blackColor];
    [btnn setTitle:@"测试按钮2" forState:UIControlStateNormal];
    [btnn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
    [btnn addTarget:self action:@selector(button2Click:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btnn];
    [btnn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.equalTo(self.view);
        make.top.equalTo(@250);
        make.size.mas_equalTo(CGSizeMake(80, 30));
    }];
}

#pragma mark - action
- (void)strongButtonClick:(UIButton *)sender{
    [self.strongButton removeFromSuperview];
    
}

- (void)weakButtonClick:(UIButton *)sender{
    [self.weakButton removeFromSuperview];
    
}

- (void)button1Click:(UIButton *)sender{
    [self.view addSubview:self.strongButton];
    [self.view addSubview:self.weakButton];
    
}

- (void)button2Click:(UIButton *)sender{
    [self.strongButton removeFromSuperview];
    self.strongButton = nil;
    
}

运行：

点击 强按钮（- (void)strongButtonClick:(UIButton *)sender 有断点），看到两个按钮都在

跑完该方法后看界面：

继续点击 弱按钮

我们再点击测试按钮1（- (void)button1Click:(UIButton *)sender 有断点）

可以看到_strongButton还是存在的，而_weakButton为nil。我们po一下

方法走完，发现界面

强按钮的frame和我们po出来的不一样。但是_strongButton出现在界面上了，而_weakButton = nil 不会出现在界面上
我们再点击 测试按钮2 ，跑完self.strongButton = nil;后

再点击 测试按钮1，_strongButton和_weakButton都不会出现在界面了。