为什么UIKit Dynamics不起作用？

Question

我正在研究iOS开发.当我添加一个rect视图并希望它受重力影响,构建并运行我的测试应用程序时,我发现它确实没有引力.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

退货UIDynamicAnimator时您将被取消分配viewDidLoad.如果它被解除分配,它就无法动画.建立一个属性:

@property (nonatomic) UIDynamicAnimator *animator;

并设置它:

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