iOS 在父边界内拖放答案

【问题标题】：iOS drag and drop within parent boundsiOS 在父边界内拖放
【发布时间】：2015-01-06 10:32:54
【问题描述】：

我尝试在 UIView 中实现一些 UIImageViews 的拖放。它目前正在工作，但您可以将图像视图拖出父级并拖出屏幕。我知道我必须检查视图是否超出了父范围。但我正在努力实现它！有人对这个有经验么？对于 Windows Phone 客户端，只需要以下行；

        var dragBehavior = new MouseDragElementBehavior {ConstrainToParentBounds = true};

我当前的手势代码在这里；

    private UIPanGestureRecognizer CreateGesture(UIImageView imageView)
    {
        float dx = 0;
        float dy = 0;

        var panGesture = new UIPanGestureRecognizer((pg) =>
        {
            if ((pg.State == UIGestureRecognizerState.Began || pg.State == UIGestureRecognizerState.Changed) && (pg.NumberOfTouches == 1))
            {
                var p0 = pg.LocationInView(View);
                if (dx == 0)
                    dx = (float)p0.X - (float)imageView.Center.X;
                if (dy == 0)
                    dy = (float)p0.Y - (float)imageView.Center.Y;

                float newX = (float)p0.X - dx;
                float newY = (float)p0.Y - dy;
                var p1 = new PointF(newX, newY);
                imageView.Center = p1;
            }
            else if (pg.State == UIGestureRecognizerState.Ended)
            {
                dx = 0;
                dy = 0;
            }
        });
        return panGesture;
    }

【问题讨论】：

标签： ios xcode uiview xamarin.ios xamarin

【解决方案1】：

我用下面的代码解决了这个问题；

        var panGesture = new UIPanGestureRecognizer((pg) =>
        {
            if ((pg.State == UIGestureRecognizerState.Began || pg.State == UIGestureRecognizerState.Changed) && (pg.NumberOfTouches == 1))
            {
                var p0 = pg.LocationInView(View);
                if (dx == 0)
                    dx = (float)p0.X - (float)imageView.Center.X;
                if (dy == 0)
                    dy = (float)p0.Y - (float)imageView.Center.Y;

                float newX = (float)p0.X - dx;
                float newY = (float)p0.Y - dy;
                var p1 = new PointF(newX, newY);


                // If too far right...
                if (p1.X > imageView.Superview.Bounds.Size.Width - (imageView.Bounds.Size.Width / 2))
                    p1.X = (float) imageView.Superview.Bounds.Size.Width - (float)imageView.Bounds.Size.Width / 2;
                else if (p1.X < 0 + (imageView.Bounds.Size.Width / 2))  // If too far left...
                    p1.X = 0 + (float)(imageView.Bounds.Size.Width / 2);

                // If too far down...
                if (p1.Y > imageView.Superview.Bounds.Size.Height - (imageView.Bounds.Size.Height / 2))
                    p1.Y = (float)imageView.Superview.Bounds.Size.Height - (float)imageView.Bounds.Size.Height / 2;
                else if (p1.Y < 0 + (imageView.Bounds.Size.Height / 2))  // If too far up...
                    p1.Y = 0 + (float)(imageView.Bounds.Size.Height / 2);

                imageView.Center = p1;
            }
            else if (pg.State == UIGestureRecognizerState.Ended)
            {
                // reset offsets when dragging ends so that they will be recalculated for next touch and drag that occurs
                dx = 0;
                dy = 0;
            }
        });

【讨论】：