iOS drag and drop within parent bounds - ios

Question

I'm try to implement drag and drop for some UIImageViews within a UIView. It is currently working, with the exception that you can drag the image views out of the parent and off the screen. I know I have to check to see if the views go outside the parent bounds.. but im struggling to achieve it! Does anyone have any experience with this? For the Windows Phone client, all that is needed is the following line;
var dragBehavior = new MouseDragElementBehavior {ConstrainToParentBounds = true};
The current gesture code I have is here;
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;
}

Answer 1

I resolved this with the following code;
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;
}
});