使用UICollisionBehavior设置边界

Question

我是ios编程的初学者。当我使用UiCollisionBehavior来设置拖放项目的边界时，我将以下代码添加到ViewController.m

#import "ViewController.h"


@interface ViewController ()

@end


@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIView *myView = [[UIView alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
    myView.backgroundColor = [UIColor grayColor];
    UIView *barrier = [[UIView alloc]initWithFrame:CGRectMake(0, 300, 130, 20)];
    barrier.backgroundColor = [UIColor redColor];
    [self.view addSubview: barrier];
    [self.view addSubview:myView];
    _animator = [[UIDynamicAnimator alloc]initWithReferenceView:myView];
    _gravity = [[UIGravityBehavior alloc]initWithItems:@[myView]];
    [_animator addBehavior:_gravity];
    _collision = [[UICollisionBehavior alloc]
                  initWithItems:@[myView]];
    _collision.translatesReferenceBoundsIntoBoundary= YES;
    [_animator addBehavior:_collision];

 }

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

@end

然而，myView并没有下降，只是停留在原来的位置。有人能告诉我原因吗？

Answer 1

替换此行，您不会在UICollisionBehavior中添加屏障

_collision = [[UICollisionBehavior alloc] initWithItems:@[myView, barrier]];