为什么UIKit动力不能工作？

Question

我现在正在学习iOS开发。当我添加一个rect视图，希望它受到重力的影响，构建并运行我的测试应用程序时，我发现它没有重力。这是我的viewController.m中的viewDidLoad代码：

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.
UIView *squre = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
squre.backgroundColor = [UIColor grayColor];
[self.view addSubview:squre];

UIDynamicAnimator *_animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
UIGravityBehavior *_gravity = [[UIGravityBehavior alloc] initWithItems:@[squre]];
[_animator addBehavior:_gravity];

Answer 1

当UIDynamicAnimator返回时，viewDidLoad将被释放。如果它被取消分配，它就不能动任何东西。使财产：

@property (nonatomic) UIDynamicAnimator *animator;

并将其设置为：

self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];