ios - 使用 uipangesturerecognizer 和自动布局查看幻灯片(垂直向上/向下跟随手指位置)

Question

这是一个非常简单的问题，但我无法弄清楚。首先，这是如何将 View 添加为 subview ，我正在使用自动布局。 (黑色) Root View 包含蓝色和橙色 View 。橙色 View 位于最上面，部分覆盖了蓝色 View 。橙色 View 中的按钮具有平移手势识别器。如果手势结束，然后橙色 View 正确定位自己，我就可以工作了。(就像覆盖蓝色 View 的照片一样，或者橙色可以向下滑动，直到只有橙色可见。)橙色 View 的位置仅使用自动布局垂直更改常数。

我面临的问题是，如果上下平移UIGestureRecognizerStateChanged，那么橙色 View 会滑向平移的相反方向。如何正确更改自动布局常量？橙色 View 的垂直移动范围是从草图中的起点向下直到橙色按钮保持可见。

#define MIN_SIZE 50
   -(void)handlePan:(UIPanGestureRecognizer *) pan
   {
   CGFloat viewHeight = pan.view.superview.height; //superView is the big orange view
if (pan.state == UIGestureRecognizerStateBegan)
{
    self.startLocation = [pan locationInView:self.view];
}

if (pan.state == UIGestureRecognizerStateChanged)
{
    CGPoint stopLocation = [pan locationInView:self.view];
    CGFloat dist = sqrt(pow((stopLocation.x - self.startLocation.x), 2) + pow((stopLocation.y - self.startLocation.y), 2));

    if (velocityOfPan.y > 0)
    {
        if (self.verticalConstraint.constant >= viewHeight - MIN_SIZE)
        {
            self.verticalConstraint.constant = viewHeight - MIN_SIZE;
        }
        else
            self.verticalConstraint.constant = dist;
    }
    else if(velocityOfPan.y < 0)
    {
        if (self.verticalConstraint.constant <= 0)
        {
            self.verticalConstraint.constant = 0;
        }
        else
        {
            self.verticalConstraint.constant = (viewHeight - MIN_SIZE - dist);
        }
    }
}
else if(pan.state == UIGestureRecognizerStateEnded)
{
    if (velocityOfPan.y > 0)
    {
        self.verticalConstraint.constant = viewHeight - MIN_SIZE;

    }
    else if (velocityOfPan.y < 0)
    {
        self.verticalConstraint.constant = 0;
    }

}

[self updateViewAnimation];
}
}

-(void) updateViewAnimation
{
[self.view updateConstraintsIfNeeded];

[UIView animateWithDuration:0.5 delay:0 usingSpringWithDamping:0.6 initialSpringVelocity:-1 options:UIViewAnimationOptionBeginFromCurrentState animations:^{
    [self.view layoutIfNeeded];
} completion:nil];
}

Answer 1

经过一番搜索和阅读，我发现我做错了什么。这是我解决问题的方法，以防万一其他人想知道。

-(void)(UIPanGestureRecognizer *) pan
{
CGPoint velocityOfPan = [pan velocityInView:self.view];
CGFloat viewHeight = pan.view.superview.height;

CGPoint delta;
switch(pan.state)
{
    case UIGestureRecognizerStateBegan:
        self.startLocation = delta = [pan translationInView:self.view];
        break;
    case UIGestureRecognizerStateChanged:
    {
        delta = CGPointApplyAffineTransform([pan translationInView:self.view], CGAffineTransformMakeTranslation(-self.startLocation.x, -self.startLocation.y));
        self.startLocation = [pan translationInView:self.view];

        if(delta.y < 0 && self.verticalConstraint.constant < 0)
        {
            delta.y = 0;
        }
        else
        {
            delta.y = self.verticalConstraint.constant + delta.y;
        }
        self.verticalConstraint.constant = delta.y;
        [self updateViewAnimation];
        break;
    }
    case UIGestureRecognizerStateEnded:
    {
        if (velocityOfPan.y > 0)
        {
            delta.y = (viewHeight - MIN_SIZE);

        }
        else if(velocityOfPan.y < 0)
        {
            delta.y = 0;
        }
        self.verticalConstraint.constant = delta.y;
        [self updateViewAnimation];
        break;
    }
    default:
        break;
}
}