UIDynamicAnimator/UIAttachmentBehavior微动？

Question

使用的Xcode 5.1.1 iOS7新的物理引擎工作时我写了下面的代码：

#import "ZViewController.h" 

@interface ZViewController() 
@property (nonatomic, strong) UIView *cardView; 
@property (nonatomic, strong) UIDynamicAnimator *animator; 
@property (nonatomic, strong) UIAttachmentBehavior *attachment; 
@end 

@implementation ZViewController 

- (void)viewDidLoad{ 
    [super viewDidLoad]; 

    self.cardView = [[UIView alloc]initWithFrame:CGRectMake(0.0, 0.0, 100.0, 100.0)]; 
    self.cardView.backgroundColor = [UIColor lightGrayColor]; 
    [self.view addSubview:self.cardView]; 

    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(panGestureHandler:)]; 
    [self.cardView addGestureRecognizer:panGestureRecognizer]; 

    self.animator = [[UIDynamicAnimator alloc]initWithReferenceView:self.view]; 
} 

- (void)viewWillAppear:(BOOL)animated{ 
    [super viewWillAppear:animated]; 

    self.cardView.center = self.view.center; 
} 

- (void)panGestureHandler:(UIPanGestureRecognizer *)panGesture{ 
    CGPoint touchPoint = [panGesture locationInView:self.view]; 
    switch(panGesture.state){ 
     case UIGestureRecognizerStateBegan: 
      self.attachment = [[UIAttachmentBehavior alloc]initWithItem:self.cardView attachedToAnchor:touchPoint]; 
      [self.animator addBehavior:self.attachment]; 
      break; 
     case UIGestureRecognizerStateChanged: 
      touchPoint.x = 160.0; 
      self.attachment.anchorPoint = touchPoint; 
      break; 
     case UIGestureRecognizerStateEnded: 
      [self.animator removeBehavior:self.attachment]; 
      self.attachment = nil; 
      break; 
     default: 
      break; 
    } 
} 

@end 

正如我在测试这个代码，我发现了一个非常奇怪的扭动/轻摇。向上和向下拖动cardView，大部分都是做预期的事情，即cardView上下滑动x轴居中，但cardView往往对角地向左移动并斜向回到x轴中心。这种摆动似乎并不一致，但似乎总是摆动到左侧。

有没有人见过这个？任何想法是什么原因造成的如何阻止它？

在此先感谢 - AYAL

Answer 1

我想你的代码，并可以复制的问题。在设定长度后，它停止了这个问题。

尝试附件的长度设置为1

case UIGestureRecognizerStateBegan: 
    self.attachment = [[UIAttachmentBehavior alloc]initWithItem:self.cardView attachedToAnchor:touchPoint]; 
    self.attachment.length = 1; 
    [self.animator addBehavior:self.attachment]; 
    break;