UIDynamic

重力行为 gravity

#import "DynamicView.h"

@interface DynamicView ()

// 仿真者
@property (strong, nonatomic) UIImageView *box;
// 仿真环境
@property (strong, nonatomic) UIDynamicAnimator *animator;

@end

@implementation DynamicView

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        _box = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"Box"]];
        _box.center = self.center;
        [self addSubview:_box];
        _animator = [[UIDynamicAnimator alloc]initWithReferenceView:self];
    }
    return self;
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  // 创建物理行为并赋给执行者
  UIGravityBehavior *gravity = [[UIGravityBehavior alloc]initWithItems:@[self.box]];
  // 设置重力方向
  gravity.gravityDirection = CGVectorMake(1, 0);
  // 设置重力的角度（默认是90°）
  gravity.angle = M_PI_2;
  // 设置重力加速度
  gravity.magnitude = 0.98;
  // 将行为添加到仿真器
  [self.animator addBehavior:gravity];
}
@end

吸附行为 snap

// 在执行捕捉之前，移除之前的行为
[self.animator removeAllBehaviors];
// 获取到触摸点
CGPoint location = [touches.anyObject locationInView:self];
// 创建捕捉行为
UISnapBehavior *snap = [[UISnapBehavior alloc]initWithItem:self.box snapToPoint:location];
    
    //设置防震系数
    //系数在（0~1之间，数值越大震动幅度越小）
    snap.damping = arc4random_uniform(100)/99.0;
    
    
    // 3.添加捕捉行为
    [self.animator addBehavior:snap];

推动行为

刚性附加

弹性附加

碰撞检测