iOS开发UIkit动力学UIDynamicAnimator一系列动画

UIDynamicAnimator类，通过这个类中的不同行为来实现一些动态特性。

UIAttachmentBehavior（吸附），UICollisionBehavior（碰撞），UIGravityBehavior（重力），UIPushBehavior（推动），UISnapBehavior（捕捉）。另外还有一个辅助的行为UIDynamicItemBehavior，用来在item层级设定一些参数，比如item的摩擦，阻力，角阻力，弹性密度和可允许的旋转等等。

1.UIAttachmentBehavior（吸附）:

- (void)viewDidLoad {
    [super viewDidLoad];

    self.dynamicAnimation = [[UIDynamicAnimator alloc]initWithReferenceView:self.view];
    // 图片
    self.imgView = [[UIImageView alloc]initWithFrame:CGRectMake(, , ,)];
    self.imgView.image = [UIImage imageNamed:@"dizhijieyong_icon"];
    [self.view addSubview:self.imgView];
    self.imgView.userInteractionEnabled = YES;

    // 添加手势
    UIPanGestureRecognizer *panGest = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(panGestAction:)];
    [self.imgView addGestureRecognizer:panGest];

    // 吸附 offset可以设置吸附的偏移，anchor是设置锚点
    self.attachment = [[UIAttachmentBehavior alloc]initWithItem:self.imgView offsetFromCenter:UIOffsetMake(, ) attachedToAnchor:CGPointMake(, )];
}

// 实现一个pan手势，让一个image跟着手势跑

- (void)panGestAction: (UIPanGestureRecognizer *)panGest{

    NSLog(@"手势触发啦!!!");

    // 取得location
    CGPoint location = [panGest locationInView:self.view];
    CGPoint boxLocation = [panGest locationInView:self.imgView];

    switch (panGest.state) {
            // 开始拖拽
        case UIGestureRecognizerStateBegan:

            NSLog(@"you touch started position %@",NSStringFromCGPoint(location));
            NSLog(@"location in image started is %@",NSStringFromCGPoint(boxLocation));
            // 移除
            [self.dynamicAnimation removeAllBehaviors];

            UIOffset offSet = UIOffsetMake(boxLocation.x - CGRectGetMidX(self.imgView.bounds),
                                           boxLocation.y - CGRectGetMidY(self.imgView.bounds));

            self.attachment = [[UIAttachmentBehavior alloc]initWithItem:self.imgView offsetFromCenter:offSet attachedToAnchor:location];
            self.attachment.damping=0.5;
            self.attachment.frequency=0.8;
            [self.dynamicAnimation addBehavior:self.attachment];
            break;
         case UIGestureRecognizerStateEnded:
            [self.dynamicAnimation removeAllBehaviors];
        default:
            [self.attachment setAnchorPoint:location];
            break;
    }
}

2.UIGravityBehavior（重力）:

// 实现点击屏幕掉落一张图片的代码

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{

    self.gravity = [[UIGravityBehavior alloc]initWithItems:nil];
    [self.dynamicAnimation addBehavior:self.gravity];

    UIImageView *gravImagView = [[UIImageView alloc]initWithFrame:CGRectMake(, , , )];
    gravImagView.image = [UIImage imageNamed:@"zichanlingyong_icon"];
    [self.view addSubview:gravImagView];
    gravImagView.frame = CGRectMake(, , , );
    [self.gravity addItem:gravImagView];

}

3.UISnapBehavior（捕捉）:

// UISnapBehavior 将UIView通过动画吸附到某个点上
- (void) handleTap:(UITapGestureRecognizer *)paramTap{
    CGPoint tapPoint = [paramTap locationInView:self.view];

    if (self.snap != nil){
        [self.dynamicAnimation removeBehavior:self.snap];
    }
    self.snap = [[UISnapBehavior alloc] initWithItem:self.imgView snapToPoint:tapPoint];
    self.snap.damping = 0.5f;  //剧列程度
    [self.dynamicAnimation addBehavior:self.snap];
}

还有一些没有试过,有时间补充吧!!!嘻嘻~~~~~