Swift - UIPanRecognizer in a UIStackView - user-interface

Question

I want to make a UIPanRecognizer in a UIStackView. The UI looks like this.
There's a big square which is a StackView which contains 9 labels.
My goal is when I start to drag my finger within the StackView and if a label contains that touchpoint then its color should be blue and on and on. If I lift my finger all of the labels background color turn back to white.
The labels are in a OutletCollection.
Here's my code:
#IBOutlet var testLabels: [UILabel]!
#IBAction func handlePan(recognizer:UIPanGestureRecognizer) {
var touchedPoint: CGPoint!
if let view = recognizer.view{
if recognizer.state == .began || recognizer.state == .changed {
touchedPoint = recognizer.location(in: view)
for index in testLabels.indices {
if testLabels[index].frame.contains(touchedPoint) {
testLabels[index].backgroundColor = UIColor.blue
}
}
}
if recognizer.state == .ended {
for index in testLabels.indices {
testLabels[index].backgroundColor = UIColor.white
}
}
}
Right now when I touch for example the top-left square and start to drag my finger to the right the whole first column turns blue then the second then the third. That happens when I touch any labels of the first row, but nothing happens when I touch the other squares.
First time, I tried to solve my problem by handle the squares just as an OutletCollection (without the StackView) and the recognizer just worked fine! The reason why I experiment with the StackView that it's so easier to make the layout(just a few constraints needed, without the StackView it is a nightmare).
I'd appreciate any help. Thank you.
Edit: probably this one helps?
Access nested stack views

Answer 1

Each label is a subview of its containing stack view (which is also probably a subview of a stack view), and each label has its own coordinate space.
Assuming your UIPanGestureRecognizer is assigned to the view controller's view, you need to translate the coordinates / frames.
This should work for you:
#IBAction func handlePan(recognizer:UIPanGestureRecognizer) {
var touchedPoint: CGPoint!
if let view = recognizer.view{
if recognizer.state == .began || recognizer.state == .changed {
touchedPoint = recognizer.location(in: view)
for index in testLabels.indices {
// translate / convert the label's bounds from its frame to the view's coordinate space
let testFrame = view.convert(testLabels[index].bounds, from:testLabels[index] )
// check the resulting testFrame for the point
if testFrame.contains(touchedPoint) {
testLabels[index].backgroundColor = UIColor.blue
}
}
}
else if recognizer.state == .ended {
for index in testLabels.indices {
testLabels[index].backgroundColor = UIColor.white
}
}
}
}
You can also simplify your code a bit by using for object in collection instead of indices. This is functionally the same as above, but maybe a little simpler:
#IBAction func handlePan(recognizer:UIPanGestureRecognizer) {
var touchedPoint: CGPoint!
if let view = recognizer.view{
if recognizer.state == .began || recognizer.state == .changed {
touchedPoint = recognizer.location(in: view)
for lbl in testLabels {
// translate / convert the label's bounds from its frame to the view's coordinate space
let testFrame = view.convert(lbl.bounds, from:lbl )
// check the resulting testFrame for the point
if testFrame.contains(touchedPoint) {
lbl.backgroundColor = .blue
}
}
}
else if recognizer.state == .ended {
for lbl in testLabels {
lbl.backgroundColor = .white
}
}
}
}