Adjust UIView frame on dragging - ios

Question

I am trying to change UIView frame on dragging. I subclassed UIView and wrote touchesBegan and touchesMoved methods. Here they are:
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
startPosition = touch?.locationInView(self)
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
let endPosition = touch?.locationInView(self)
let difference = endPosition!.y - startPosition.y
let newFrame = CGRectMake(self.frame.origin.x, self.frame.origin.y, self.frame.width, self.frame.height + difference)
self.frame = newFrame
}
But as a result I got unexpected behaviour. It is a little bit hard to describe it. Here's video how it works.. Small drag(about 20px) makes frame bigger on approximately 100px.
I also have some constraints on my custom view. Image at the bottom of custom view should stay always there:
So questions are:
How to make view bigger on distance user dragged.
And why constraints do not apply after changing frame and how to apply them again?

Answer 1

The reason your view is growing quickly is that you are always updating the current view height with the distance you have moved since your first touch down. Instead of modifying the current height, you should always add the distance moved to the original height of the view.
Add another property to your custom view to keep track of the original height of the view. Set it in touchesBegan and then use that originalHeight when computing the frame in touchesMoved:
class CustomView: UIView {
var startPosition: CGPoint?
var originalHeight: CGFloat = 0
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
startPosition = touch?.locationInView(self)
originalHeight = self.frame.height
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
let endPosition = touch?.locationInView(self)
let difference = endPosition!.y - startPosition!.y
let newFrame = CGRectMake(self.frame.origin.x, self.frame.origin.y, self.frame.width, originalHeight + difference)
self.frame = newFrame
}
}
And why constraints do not apply after changing frame and how to apply
them again?
You really shouldn't be updating frames when using Auto Layout. The correct way to do this is to add an #IBOutlet to the height constraint for your view and then update the constant property of the constraint when you wish to change the height of your view.
When you do that, Auto Layout will correctly position the subviews of your custom view using the updated height.
To add an #IBOutlet to the height constraint to your code, Control-drag from the height constraint in the Document Outline to your viewController. Give it a name such as customViewHeight.
Since your code for updating the height of the view is in the view code itself, have the viewController assign the height constraint to the custom view in viewDidLoad. Then the custom view can update the constant property of the height constraint to resize the view.
class ViewController: UIViewController {
#IBOutlet weak var customViewHeight: NSLayoutConstraint!
#IBOutlet weak var customView: CustomView!
override func viewDidLoad() {
super.viewDidLoad()
// Assign the layout constraint to the custom view so that it can update it itself
customView.customViewHeight = customViewHeight
}
}
class CustomView: UIView {
var startPosition: CGPoint?
var originalHeight: CGFloat = 0
var customViewHeight: NSLayoutConstraint!
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
startPosition = touch?.locationInView(self)
originalHeight = customViewHeight.constant
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
let touch = touches.first
let endPosition = touch?.locationInView(self)
let difference = endPosition!.y - startPosition!.y
customViewHeight.constant = originalHeight + difference
}
}

Answer 2

In your case, I think you should change the constant of the bottom constraints instead of changing the frame of the view. And by the way, you'd better use gestures instead of overriding touch methods since gestures are higher level API and easier to maintain
Basically, projects using Autolayout should avoid changing views with frame.