Stop UIView from going off screen

Question

I have a UIView that is a circle. That is all the app is - I can move the circle around the screen using a UIPanGestureRecognizer. Now I don't want my circle to be able to be dragged off screen. For example, if I drag the circle to the right, it should stop moving the circle when the right edge hits the edge of the window.

Here is my code:

 switch rec.state {
        case .Began:
            x = fingerLocation.x - (myView?.center.x)!
            y = fingerLocation.y - (myView?.center.y)!
            break


        case .Changed:
            myView?.center.x = fingerLocation.x - x
            myView?.center.y = fingerLocation.y - y

            if (myView?.center.x)! + (myView!.bounds.width/2) >= view.bounds.width {
                myView?.center.x = view.bounds.width - myView!.bounds.width/2
            }
            break
        case .Ended:
            myView?.center = CGPointMake(fingerLocation.x - x, fingerLocation.y - y)
            break
}

This code works if I drag the circle slowly toward the edge. If I drag quickly, the circle will go over the edge, and jump back into view the second another .Changed state is sent. How can I stop the circle from ever going over the edge?

Answer 1

You could check first if the fingerLocation would result in an offscreen view,
and move the view only if it would not move offscreen.

case .Changed: 
   let currentRightEdge = CGRectGetMaxX(myView!.frame)
   let potentialRightEdge = currentRightEdge + fingerLocation.x - x
   if  potentialRightEdge >= view.bounds.width {
     myView?.center.x = view.bounds.width - myView!.bounds.width/2
   }
   else {
     myView?.center.x = potentialRightEdge
   }
   myView?.center.y = fingerLocation.y - y

Also, I do not think you need the break in Swift ;-).

Answer 2

The problem might be that if the view goes offscreen, you set the myView?.center.x twice. Try this:

case .Changed:
            myView?.center.y = fingerLocation.y - y
            var newX : Int = fingerLocation.x - x

            if (newX + (myView!.bounds.width/2)) >= view.bounds.width {
                myView?.center.x = view.bounds.width - myView!.bounds.width/2
            } else {
                myView?.center.x = newX
            }
            break

Answer 3

Try something like this:

case .Changed:
    var targetX = fingerLocation.x - x
    if targetX < 0 {
        targetX = 0
    } else if targetX > CGRectGetWidth(view.bounds) {
        targetX = CGRectGetWidth(view.bounds)
    }

    var targetY = fingerLocation.y - y
    if targetY < 0 {
        targetY = 0
    } else if targetY > CGRectGetHeight(view.bounds) {
        targetY = CGRectGetHeight(view.bounds)
    }

    myView?.center = CGPoint(x: targetX, y: targetY)