UIStackView : Is it really necessary to call both removeFromSuperView and removeArrangedSubview to remove a subview?

No, just call subview.removeFromSuperview()

/* Removes a subview from the list of arranged subviews without removing it as
 a subview of the receiver.
    To remove the view as a subview, send it -removeFromSuperview as usual;
 the relevant UIStackView will remove it from its arrangedSubviews list
 automatically.
 */
open func removeArrangedSubview(_ view: UIView)

In iOS 12.0, You need to use

stackView.arrangedSubviews[index].removeFromSuperview()

If you use removeArrangedSubview, there is a bug where the view at the specified index removed, but the view I want to clear appears at CGPoint(x: 0, y: 0).

Hope this help someone.

Hacking With Swift provides a pretty good example and explanation, using Web views in this case.

The reason is that you can remove something from a stack view's arranged subview list then re-add it later, without having to recreate it each time – it was hidden, not destroyed. We don't want a memory leak, so we want to remove deleted web views entirely. If you find your memory usage ballooning, you probably forgot this step!

https://www.hackingwithswift.com/read/31/4/removing-views-from-a-uistackview-with-removearrangedsubview

To remove a arrangedSubview from a stackview is

// To remove it from the view hierarchy
   subView.removeFromSuperview()

No, To remove specific view.

func removeArrangedSubview(_ view: UIView)

To remove all subviews

stackView.arrangedSubviews.forEach { $0.removeFromSuperview() }

You're right, just the call to removeFromSuperview is sufficient to have the view fully removed.

I suspect the reason for people putting both is because they run across the removeArrangedSubview documentation which seems to say both are needed. (And indeed, they are, if you call removeArrangedSubview and want the view really gone.)

The additional doc in arrangedSubviews is not seen by so many, so they don't realize removeArrangedSubview is, in this case, optional.

For removing i use this extension. Don't really know is it necessary to remove constraints. But maybe it would help.

extension UIStackView {
    func removeAllArrangedSubviews() {
        let removedSubviews = arrangedSubviews.reduce([]) { (allSubviews, subview) -> [UIView] in
            self.removeArrangedSubview(subview)
            return allSubviews + [subview]
        }

        for v in removedSubviews {
            if v.superview != nil {
                NSLayoutConstraint.deactivate(v.constraints)
                v.removeFromSuperview()
            }
        }
    }
}

I will suggest get arranged subviews then remove it like below code .

for view in self.stackView.arrangedSubviews{
      self.stackView.removeArrangedSubview(view)
      view.removeFromSuperview()
}

Simple answer: NO! (as previously stated by many others)

Longer answer:

// to remove "view" from the stack entirely 
// calls removeArrangedSubview()
view.removeFromSuperview() 

// to add "view" to the stack
// calls addSubview()
stackView.addArrangeSubview(view)

Please check out the explicit paragraph in Apple's documentation about this issue (Maintain consistency between the arranged views and subview): https://developer.apple.com/documentation/uikit/uistackview#1653129

Here is the important part:

The stack view ensures that its arrangedSubviews property is always a subset of its subviews property. Specifically, the stack view enforces the following rules: When the stack view adds a view to its arrangedSubviews array, it also adds that view as a subview, if it isn’t already. When a subview is removed from the stack view, the stack view also removes it from the arrangedSubviews array. Removing a view from the arrangedSubviews array doesn’t remove it as a subview. The stack view no longer manages the view’s size and position, but the view is still part of the view hierarchy, and is rendered on screen if it’s visible.