ios - 如果不将UIgravity声明为属性，原因是什么？

Question

好的，所以我开始学习UIDynamics，只想在小盒子上解决它。
我在ViewController.m中声明了UIGravityBehaviour和UIDynamicsBehaviour并对UIView进行了编码，但是当我执行代码时，它不起作用。
但是正如我在.h文件中将它们声明为@property一样，该程序也可以正常工作。
背后的原因是什么？
将其声明为@property和不将其声明为@property有什么区别？

这是我的文件。

在使用@property之前

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@end

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

}

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

@end

声明为@property后

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (strong,nonatomic) UIDynamicAnimator* myAnimator ;
@property (strong,nonatomic) UIGravityBehavior *gravityBehavior;
@property (strong,nonatomic) UICollisionBehavior *collisionBehavior ;
@end

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];
    self.myAnimator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    self.gravityBehavior = [[UIGravityBehavior alloc] initWithItems:@[box]];
    self.collisionBehavior = [[UICollisionBehavior alloc] initWithItems:@[box]];
    self.collisionBehavior.translatesReferenceBoundsIntoBoundary = YES;
    [self.myAnimator addBehavior:self.gravityBehavior];
    [self.myAnimator addBehavior:self.collisionBehavior];
}

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

@end

Answer 1

您不必将UIGravityBehavior移至某个属性，只需将UIDynamicAnimator移至该属性即可。但是，如果您要删除特定的重力行为而不是一次删除所有重力行为，则无论如何都是个好主意。