附著-UIAttachmentBehavior

物理模擬中的附著行為的實現同之前’捕捉’步驟
1.建立物理模擬器物件
2.建立物理模擬行為物件
3.設定物理模擬行為的屬性
4.將模擬行為新增到物理模擬器中

@property (weak, nonatomic) IBOutlet UIView *testViewOne;
@property (weak, nonatomic) IBOutlet UIView *testViewTwo;

@property (nonatomic, strong) UIDynamicAnimator *animator;

- (void
 
)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    self.testViewOne.layer.cornerRadius = 25;

    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewDidTapGesture:)];

    [self
 
.view addGestureRecognizer:tapGesture];
}

- (void)viewDidTapGesture:(UIPanGestureRecognizer *)tapGesture {
    CGPoint currentPanPoint = [tapGesture locationInView:self.view];

    //建立物理模擬器
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

    //建立重力模擬行為
    UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[self
 
.testViewOne, self.testViewTwo]];

    //設定重力模擬行為的屬性(引數)
    //    CGVector gravityDirection
    //    CGFloat angle
    //    CGFloat magnitude
    gravity.gravityDirection = CGVectorMake(0, 1);
    gravity.magnitude = 1;

    ZHJView *view = (ZHJView *)self.view;

    [gravity setAction:^{
        view.startPoint = currentPanPoint;
        view.endPointOne = self.testViewOne.center;

        CGPoint point = CGPointZero;

        view.endPointTwo = [self.view convertPoint:point fromView:self.testViewTwo];
    }];

    //建立附著模擬行為
    UIAttachmentBehavior *attachmentOne = [[UIAttachmentBehavior alloc] initWithItem:self.testViewOne attachedToAnchor:currentPanPoint];

    //UIAttachmentBehavior *attachmentTwo = [[UIAttachmentBehavior alloc] initWithItem:self.testViewTwo attachedToAnchor:currentPanPoint];

    //預設是和物體的中心點附著...修改中心點的偏移量 ,附著左上角
    CGSize size = self.testViewTwo.bounds.size; //myView的size
    UIOffset offset = UIOffsetMake(- size.width * 0.5, - size.height * 0.5);

    UIAttachmentBehavior *attachmentTwo = [[UIAttachmentBehavior alloc] initWithItem:self.testViewTwo offsetFromCenter:offset attachedToAnchor:currentPanPoint];


    //新增模擬行為
    [self.animator addBehavior:gravity];
    [self.animator addBehavior:attachmentOne];
    [self.animator addBehavior:attachmentTwo];
//    [self.animator addBehavior:collision];

}

其中要注意的點可能就是控制元件和觸控點選點間的連線繪製，這裡要自定義一個view(我定義的是ZHJView)的類來描述控制器viewController的View
在ZHJView類中獲取手指觸控的點以及控制元件的錨點
在.h檔案中宣告

@property (nonatomic, assign) CGPoint startPoint;

@property (nonatomic, assign) CGPoint endPointOne;

@property (nonatomic, assign) CGPoint endPointTwo;

在.m檔案中重寫startPoint的set方法以及drawRect: ，因為drawRect:方法不能手動呼叫，所以在設定startPoint的時候需要重繪，見程式碼

- (void)setStartPoint:(CGPoint)startPoint {
    _startPoint = startPoint;

    //重繪
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {

    //建立Bezier路徑
    UIBezierPath *path = [UIBezierPath bezierPath];

    [path moveToPoint:self.startPoint];

    [path addLineToPoint:self.endPointOne];

    [path moveToPoint:self.startPoint];

    [path addLineToPoint:self.endPointTwo];

    //描邊
    [path stroke];

}

物理模擬原始碼下載