Ios 具有`NSLayoutConstraint'的内存泄漏`

我有一个简单的布局，带有连接两个视图的约束，并将该约束存储在强属性中

我的期望是，在删除其中一个视图后，约束仍将存在，但它将变为非活动状态。但事实并非如此，我的应用程序因异常而崩溃

幸运的是，我能够重现这个问题。我附上视图控制器的源代码。您可以将其粘贴到使用“单视图应用程序”模板创建的新项目中

要再现问题，请在删除其中一个视图之前和之后打印约束描述。有一次，约束没有被移除，代码也正常工作（但只发生了一次）。通过调试器，我可以检查我删除的视图是否也没有解除分配，而它已经没有层，因此它的某些部分已经解构。事情发生后，我注释掉了

printConstraintDescriptionButtouchedupInside

的实现，并在

RemoveViewButtonCouchedupInside

中设置断点。当调试器在第二次按下按钮后暂停应用程序时，约束不再存在

是否不允许持有对

NSLayoutConstraint

实例的强引用？我在文档中没有找到该信息

使用Xcode版本10.1（10B61）编译，运行iOS模拟器iPhone SE 12.1。在运行iOS 12.1.3（16D5032a）和11.2.2（15C202）的物理设备上，相同的逻辑（但不在独立代码段中）失败。使用Xcode 9.4.1版编译不会改变任何东西

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@property (strong, nonatomic) UIView* topView;
@property (strong, nonatomic) UIView* bottomView;

@property (strong, nonatomic) NSLayoutConstraint* constraint;

@property (strong, nonatomic) UIButton* removeViewButton;
@property (strong, nonatomic) UIButton* printConstraintDescriptionButton;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.topView = [UIView new];
    self.topView.backgroundColor = [UIColor grayColor];
    self.topView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:self.topView];

    self.bottomView = [UIView new];
    self.bottomView.backgroundColor = [UIColor grayColor];
    self.bottomView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:self.bottomView];

    self.removeViewButton = [UIButton buttonWithType:UIButtonTypeSystem];
    self.removeViewButton.translatesAutoresizingMaskIntoConstraints = NO;
    [self.removeViewButton setTitle:@"Remove View"
                           forState:UIControlStateNormal];
    [self.removeViewButton addTarget:self
                              action:@selector(removeViewButtonTouchedUpInside)
                    forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.removeViewButton];

    self.printConstraintDescriptionButton = [UIButton buttonWithType:UIButtonTypeSystem];
    self.printConstraintDescriptionButton.translatesAutoresizingMaskIntoConstraints = NO;
    [self.printConstraintDescriptionButton setTitle:@"Print Constraint Description"
                                           forState:UIControlStateNormal];
    [self.printConstraintDescriptionButton addTarget:self
                                              action:@selector(printConstraintDescriptionButtonTouchedUpInside)
                                    forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.printConstraintDescriptionButton];

    NSDictionary* views = @{
                            @"topView": self.topView,
                            @"bottomView": self.bottomView,
                            @"removeViewButton": self.removeViewButton,
                            @"printConstraintDescriptionButton": self.printConstraintDescriptionButton
    };

    NSArray<NSString*>* constraints = @[
                             @"H:|-[topView]-|",
                             @"H:|-[bottomView]-|",
                             @"H:|-[printConstraintDescriptionButton]-|",
                             @"H:|-[removeViewButton]-|",
                             @"V:|-[topView(==44)]",
                             @"V:[bottomView(==44)]",
                             @"V:[printConstraintDescriptionButton]-[removeViewButton]-|"
    ];

    [constraints enumerateObjectsUsingBlock:^(NSString * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:obj
                                                                          options:0
                                                                          metrics:nil
                                                                            views:views]];
    }];

    self.constraint = [NSLayoutConstraint constraintWithItem:self.topView
                                                   attribute:NSLayoutAttributeBottom
                                                   relatedBy:NSLayoutRelationEqual
                                                      toItem:self.bottomView
                                                   attribute:NSLayoutAttributeTop
                                                  multiplier:1.0
                                                    constant:-8.0];
    self.constraint.active = YES;
}

- (void)printConstraintDescriptionButtonTouchedUpInside {
    NSLog(@"%@", self.constraint);
}

- (void)removeViewButtonTouchedUpInside {
    [self.bottomView removeFromSuperview];
    self.bottomView = nil;
}

@end

#导入“ViewController.h”
@界面视图控制器（）
@属性（强，非原子）UIView*topView；
@属性（强，非原子）UIView*bottomView；
@属性（强，非原子）NSLayoutConstraint*约束；
@属性（强，非原子）UIButton*removeViewButton；
@属性（强，非原子）UIButton*printConstraintDescriptionButton；
@结束
@实现视图控制器
-（无效）viewDidLoad{
[超级视图下载]；
self.topView=[UIView new]；
self.topView.backgroundColor=[UIColor grayColor]；
self.topView.translatesAutoResizengMaskintoConstraints=否；
[self.view addSubview:self.topView]；
self.bottomView=[UIView new]；
self.bottomView.backgroundColor=[UIColor grayColor]；
self.bottomView.translatesAutoResizengmaskintoConstraints=否；
[self.view addSubview:self.bottomView]；
self.removeViewButton=[UIButton Button类型：UIButtonTypeSystem]；
self.removeViewButton.translatesAutoResizengMaskintoConstraints=否；
[self.removeViewButton集合标题：@“删除视图”
forState:uicontrol状态正常]；
[self.removeViewButton添加目标：self
操作：@选择器（移除ViewButtonToucheDupInside）
forControlEvents:UIControlEventTouchUpInside]；
[self.view addSubview:self.removeViewButton]；
self.printConstraintDescriptionButton=[UIButton Button类型：UIButtonTypeSystem]；
self.printConstraintDescriptionButton.translatesAutoReshizingMaskintoConstraints=否；
[self.printConstraintDescriptionButton集合标题：@“打印约束说明”
forState:uicontrol状态正常]；
[self.printConstraintDescriptionButton添加目标：self
操作：@selector（PrintConstraintDescriptionButtontTouchedupInside）
forControlEvents:UIControlEventTouchUpInside]；
[self.view addSubview:self.printConstraintDescriptionButton]；
NSDictionary*视图=@{
@“topView”：self.topView，
@“bottomView”：self.bottomView，
@“removeViewButton”：self.removeViewButton，
@“printConstraintDescriptionButton”：self.printConstraintDescriptionButton
};
NSArray*约束=@[
@“H:|-[topView]-|”，
@“H:|-[bottomView]-|”，
@“H:|-[printConstraintDescriptionButton]-|”，
@“H:|-[removeViewButton]-|”，
@“V:|-[顶视图（=44）]”，
@“V:[底部视图（=44）]”，
@“V:[printConstraintDescriptionButton]-[removeViewButton]-|”
];
[constraints enumerateObjectsUsingBlock:^（NSString*\u非空obj，NSUInteger idx，BOOL*\u非空stop）{
[self.view addConstraints:[NSLayoutConstraints Constraints WithVisualFormat:obj
选项：0
指标：零
视图：视图]]；
}];
self.constraint=[NSLayoutConstraint constraintWithItem:self.topView
属性：NSLAYUTATTRIBUTEBOTTOM
关系人：NSLayoutRelationEqual
toItem:self.bottomView
属性：NSLAYUTATTRIBUTETOP
乘数：1.0
常数：-8.0]；
self.constraint.active=是；
}
-（无效）打印约束描述按钮内部{
NSLog（@“%@”，自约束）；
}
-（无效）将ViewButton从内部移除{
[self.bottomView从superview移除]；
self.bottomView=nil；
}
@结束

问题不在于约束不再存在。。。问题在于：

NSLog(@"%@", self.constraint);

尝试打印约束的（默认）说明。如果约束未激活，则将抛出EXC_BAD_访问

- (void)printConstraintDescriptionButtonTouchedUpInside {

    NSLog(@"self.constraint still exists? %@", self.constraint != nil ? @"Yes" : @"No");

    NSLog(@"self.constraint.constant = %0.2f", self.constraint.constant);

    if (self.constraint.isActive) {
        NSLog(@"self.constraint (default description) %@", self.constraint);
    } else {
        // this will throw EXC_BAD_ACCESS exception if constraint is not active
        // so, don't do it
        //NSLog(@"self.constraint (default description) %@", self.constraint);
    }

}