使用UIAttachmentBehavior拖動視圖

Question

我想拖動一個UIView，讓它移動附加到其上的其他視圖的位置，就像它們都是通過字符串連接一樣。 起始狀態將是一堆UIViews聚集在一起。 如果你拉出一個項目，它附加的項目將在它與被拖動的視圖之間達到最小距離后開始移動。 我認為實現這一目標的最佳方法是使用UIDynamicItemBehavior，考慮到我需要將其重新捕捉到適當位置並對其施加權重。 如果不做荒謬的代碼，我不太清楚如何實現這一點。 我所擁有的代碼可以在下面看到。 不幸的是，我遇到的問題是被拖動的方形項目回到了square2。 如果有人有任何建議，我會很樂意澄清是否需要。

- (void)viewDidLoad
{
    [super viewDidLoad];

    _containmentView = [[UIView alloc] initWithFrame:CGRectMake(0.0, self.view.frame.size.height/2, self.view.frame.size.width, 200)];
    [self.view addSubview:_containmentView];
    [_containmentView setBackgroundColor:[UIColor greenColor]];

    _square = [[UIView alloc]initWithFrame:CGRectMake(200, 0, 100, 100)];
    _square.backgroundColor = [UIColor yellowColor];
    [_containmentView addSubview:_square];

    _square2 = [[UIView alloc]initWithFrame:CGRectMake(100, 0, 100, 100)];
    _square2.backgroundColor = [UIColor redColor];
    [_containmentView addSubview:_square2];


    _animator = [[UIDynamicAnimator alloc]initWithReferenceView:_containmentView];
    _gravity = [[UIGravityBehavior alloc]initWithItems:@[_square, _square2]];
    _gravity.gravityDirection = CGVectorMake(-1.0, 0.0);
    [_animator addBehavior:_gravity];

    _collision = [[UICollisionBehavior alloc]initWithItems:@[_square]];
    _collision.collisionDelegate = self;
    _collision.translatesReferenceBoundsIntoBoundary = YES; //causes the boundary to use the bounds of the reference view supplied to the UIDynamicAnimator




    [_animator addBehavior:_collision];


    UIDynamicItemBehavior *itemBehaviour = [[UIDynamicItemBehavior alloc] initWithItems:@[_square]];
    itemBehaviour.elasticity = 0.6;
    [_animator addBehavior:itemBehaviour];

    UIPanGestureRecognizer *gesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    [_square addGestureRecognizer:gesture];

    UIAttachmentBehavior *attach = [[UIAttachmentBehavior alloc] initWithItem:_square2 attachedToItem:_square];
    [_animator addBehavior:attach];

}

-(void)handlePan:(UIPanGestureRecognizer *)gesture
{
    CGPoint touchPoint = [gesture locationInView:self.view];
    UIView* draggedView = gesture.view;

    if (gesture.state == UIGestureRecognizerStateBegan) {
        // 1. was the pan initiated from the upper part of the recipe?
        UIView* draggedView = gesture.view;
        CGPoint dragStartLocation = [gesture locationInView:draggedView];
            _draggingView = YES;
            _previousTouchPoint = touchPoint;
//            [_animator updateItemUsingCurrentState:draggedView];

    } else if (gesture.state == UIGestureRecognizerStateChanged && _draggingView) {
        // 2. handle dragging
        float xOffset = _previousTouchPoint.x - touchPoint.x;
        gesture.view.center = CGPointMake(draggedView.center.x - xOffset,
                                          draggedView.center.y);
        _previousTouchPoint = touchPoint;
//        [_animator updateItemUsingCurrentState:draggedView];

    } else if (gesture.state == UIGestureRecognizerStateEnded && _draggingView) {
        // 3. the gesture has ended
//        [self tryDockView:draggedView];
//        [self addVelocityToView:draggedView fromGesture:gesture];
        [_animator updateItemUsingCurrentState:draggedView];
        _draggingView = NO;
    }

}

Answer 1

您需要使用附件拖動您的形狀，因此動畫師可以使用其物理引擎計算每個項目位置。

這是你viewDidLoad更新：

- (void)viewDidLoad
{
    [super viewDidLoad];

    _containmentView = [[UIView alloc] initWithFrame:CGRectMake(0.0, self.view.frame.size.height/2, self.view.frame.size.width, 200)];
    [self.view addSubview:_containmentView];
    [_containmentView setBackgroundColor:[UIColor greenColor]];

    _square = [[UIView alloc]initWithFrame:CGRectMake(200, 0, 100, 100)];
    _square.backgroundColor = [UIColor yellowColor];
    [_containmentView addSubview:_square];

    _square2 = [[UIView alloc]initWithFrame:CGRectMake(100, 0, 100, 100)];
    _square2.backgroundColor = [UIColor redColor];
    [_containmentView addSubview:_square2];

    _animator = [[UIDynamicAnimator alloc]initWithReferenceView:_containmentView];
    _gravity = [[UIGravityBehavior alloc]initWithItems:@[_square, _square2]];
    _gravity.gravityDirection = CGVectorMake(-1.0, 0.0);
    [_animator addBehavior:_gravity];

    _collision = [[UICollisionBehavior alloc]initWithItems:@[_square, _square2]];
    _collision.translatesReferenceBoundsIntoBoundary = YES;

    [_animator addBehavior:_collision];


    UIDynamicItemBehavior *itemBehaviour = [[UIDynamicItemBehavior alloc] initWithItems:@[_square, _square2]];
    itemBehaviour.elasticity = 0.6;
    [_animator addBehavior:itemBehaviour];

    UIPanGestureRecognizer *gesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    [_square addGestureRecognizer:gesture];

    UIPanGestureRecognizer *gesture2 = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    [_square2 addGestureRecognizer:gesture2];

    UIAttachmentBehavior *attach = [[UIAttachmentBehavior alloc] initWithItem:_square2 attachedToItem:_square];
    attach.damping = 1.6;
    attach.frequency = 10;
    [_animator addBehavior:attach];

}

我為這兩種形狀添加了重力，平移和碰撞。

這里應該看看你的handlePan方法：

-(void)handlePan:(UIPanGestureRecognizer *)gesture
{
    CGPoint touchPoint = [gesture locationInView:_containmentView];
    UIView* draggedView = gesture.view;

    if (gesture.state == UIGestureRecognizerStateBegan) {
        // 1. was the pan initiated from the upper part of the recipe?
        _draggingView = YES;
        _previousTouchPoint = touchPoint;
        // Add a new attachment on the selected view;
        self.attachment = [[UIAttachmentBehavior alloc] initWithItem:draggedView attachedToAnchor:touchPoint];
        [self.animator addBehavior:self.attachment];
        // Could temporarily remove gravity here

    } else if (gesture.state == UIGestureRecognizerStateChanged && _draggingView) {
        // 2. handle dragging
        [self.attachment setAnchorPoint:touchPoint];

    } else if (gesture.state == UIGestureRecognizerStateEnded && _draggingView) {
        // 3. the gesture has ended
        _draggingView = NO;
        [self.animator removeBehavior:self.attachment];
        // If gravity was removed, add it back here
    }
}

您可能希望在拖動時暫時移除重力。 只需看看我的評論，看看你能做到哪里（並且不要忘記在拖動結束時把它放回去）。

正如您所看到的，您真的需要更少的編碼來處理手勢:)

您可以使用附件的阻尼，頻率和長度來使形狀對拖動手勢做出不同的反應。 您還可以使用UIDynamicItemBehavior的density屬性為形狀添加density 。