爲什麼UIKit Dynamics不起作用？

Question

我正在學習iOS開發。當我添加矩形視圖並希望受重力影響時，構建並運行我的測試應用程序，我發現它沒有重力。 這是viewDidLoad中的代碼在我viewController.m：

[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

你UIDynamicAnimator被釋放時viewDidLoad回報。如果它被釋放，它不能動畫。使屬性：

@property (nonatomic) UIDynamicAnimator *animator; 

，並設置：

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