UIGravityBehavior无效

Question

我正在尝试学习UIKit Dynamics 我创建了一个盒子视图并在其上添加了UIGravityBehavior，但是当我运行Project时没有任何反应！

Viewcontroller.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIView* box = [[UIView alloc]initWithFrame:CGRectMake(100, 50, 100, 100)];
    box.backgroundColor = [UIColor blackColor];
    [self.view addSubview:box];
    UIGravityBehavior* gravityBehaviour = [[UIGravityBehavior alloc]init];
    [gravityBehaviour addItem:box];
    UIDynamicAnimator* myAnimator = [[UIDynamicAnimator alloc]initWithReferenceView:self.view];
    [myAnimator addBehavior:gravityBehaviour];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

这是我的视图controller.m文件。
程序有什么问题？

Answer 1

如果要在ViewDidLoad中使用它，则需要将UIDynamicAnimator和UIGravityBehavior声明为当前VC的属性。自动引用计数将在ViewDidLoad完成后释放这些对象。

此致

Answer 2

你能尝试一下吗：

UIView* box = [[UIView alloc]initWithFrame:CGRectMake(100, 50, 100, 100)];
box.backgroundColor = [UIColor blackColor];
[self.view addSubview:box];

UIDynamicAnimator* myAnimator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
UIGravityBehavior* gravityBehaviour = [[UIGravityBehavior alloc] initWithItems:@[box]];
[myAnimator addBehavior: gravityBehaviour];

// EXTENDED

在.m文件中尝试创建实例变量：

UIDynamicAnimator* _animator;
UIGravityBehavior* _gravity;

在viewDidLoad中创建您的框视图，然后添加：

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

它应该排序你的问题。

Answer 3

有一个关于使用UIGravityBehavior在这里创建应用程序的非常基本的教程：https://www.youtube.com/watch?v=vKqjKcVUYPc - 希望它有所帮助。

Answer 4

我认为您必须将UIDynamicAnimator实例声明为Strong类型。

例如，您可以将UIDynamicAnimator定义为UIViewController的成员。

@interface ViewController ()
    @property (nonatomic, strong) UIDynamicAnimator *animator;
@end

然后在你的viewDidLoad

中

// ... code to init your self.animator and add behaviors
self.animator = animator;