Drag UIView between UIViews
Call [[touches anyObject] locationInView: self.superview] to get the point under the finger in the container view. Then send self.superview -hitTest:withEvent: to find out the view X is inside. Note that it will always return X, so you will have to override either -pointIsInside:withEvent: or -hitTest:withEvent: to return nil while you're dragging. This kind of kludge is the reason I would implement such tracking in the container view, rather than in a dragged view.
With Swift 5 and iOS 12, you can solve your problem with Drag and Drop APIs. The following sample code shows how to do.
ViewContainer.swift
import MobileCoreServices
import UIKit
enum ViewContainerError: Error {
case invalidType, unarchiveFailure
}
class ViewContainer: NSObject {
let view: UIView
required init(view: UIView) {
self.view = view
}
}
extension ViewContainer: NSItemProviderReading {
static var readableTypeIdentifiersForItemProvider = [kUTTypeData as String]
static func object(withItemProviderData data: Data, typeIdentifier: String) throws -> Self {
if typeIdentifier == kUTTypeData as String {
guard let view = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) as? UIView else { throw ViewContainerError.unarchiveFailure }
return self.init(view: view)
} else {
throw ViewContainerError.invalidType
}
}
}
extension ViewContainer: NSItemProviderWriting {
static var writableTypeIdentifiersForItemProvider = [kUTTypeData as String]
func loadData(withTypeIdentifier typeIdentifier: String, forItemProviderCompletionHandler completionHandler: @escaping (Data?, Error?) -> Void) -> Progress? {
if typeIdentifier == kUTTypeData as String {
do {
let data = try NSKeyedArchiver.archivedData(withRootObject: view, requiringSecureCoding: false)
completionHandler(data, nil)
} catch {
completionHandler(nil, error)
}
} else {
completionHandler(nil, ViewContainerError.invalidType)
}
return nil
}
}
ViewController.swift
import UIKit
class ViewController: UIViewController {
let redView = UIView()
let greenView = UIView()
override func viewDidLoad() {
super.viewDidLoad()
let blueView = UIView()
blueView.backgroundColor = .blue
greenView.backgroundColor = .green
greenView.isUserInteractionEnabled = true
greenView.addSubview(blueView)
setConstraintsInSuperView(forView: blueView)
redView.backgroundColor = .red
redView.isUserInteractionEnabled = true
let greenViewDropInteraction = UIDropInteraction(delegate: self)
let greenViewDragInteraction = UIDragInteraction(delegate: self)
greenViewDragInteraction.isEnabled = true
greenView.addInteraction(greenViewDragInteraction)
greenView.addInteraction(greenViewDropInteraction)
let redViewDropInteraction = UIDropInteraction(delegate: self)
let redViewDragInteraction = UIDragInteraction(delegate: self)
redViewDragInteraction.isEnabled = true
redView.addInteraction(redViewDragInteraction)
redView.addInteraction(redViewDropInteraction)
let stackView = UIStackView(arrangedSubviews: [greenView, redView])
view.addSubview(stackView)
stackView.distribution = .fillEqually
stackView.frame = view.bounds
stackView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
}
}
extension ViewController {
// MARK: Helper methods
func setConstraintsInSuperView(forView subView: UIView) {
subView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate(NSLayoutConstraint.constraints(withVisualFormat: "H:|-[subView]-|", options: [], metrics: nil, views: ["subView": subView]))
NSLayoutConstraint.activate(NSLayoutConstraint.constraints(withVisualFormat: "V:|-[subView]-|", options: [], metrics: nil, views: ["subView": subView]))
}
}
extension ViewController: UIDragInteractionDelegate {
func dragInteraction(_ interaction: UIDragInteraction, itemsForBeginning session: UIDragSession) -> [UIDragItem] {
guard let containedView = interaction.view?.subviews.first else { return [] }
let viewContainer = ViewContainer(view: containedView)
let itemProvider = NSItemProvider(object: viewContainer)
let item = UIDragItem(itemProvider: itemProvider)
item.localObject = viewContainer.view
return [item]
}
func dragInteraction(_ interaction: UIDragInteraction, sessionWillBegin session: UIDragSession) {
guard let containedView = interaction.view?.subviews.first else { return }
containedView.removeFromSuperview()
}
func dragInteraction(_ interaction: UIDragInteraction, previewForLifting item: UIDragItem, session: UIDragSession) -> UITargetedDragPreview? {
guard let containedView = interaction.view?.subviews.first else { return nil }
return UITargetedDragPreview(view: containedView)
}
func dragInteraction(_ interaction: UIDragInteraction, item: UIDragItem, willAnimateCancelWith animator: UIDragAnimating) {
animator.addCompletion { _ in
guard let containedView = item.localObject as? UIView else { return }
interaction.view!.addSubview(containedView)
self.setConstraintsInSuperView(forView: containedView)
}
}
func dragInteraction(_ interaction: UIDragInteraction, prefersFullSizePreviewsFor session: UIDragSession) -> Bool {
return true
}
}
extension ViewController: UIDropInteractionDelegate {
func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool {
return session.canLoadObjects(ofClass: ViewContainer.self) && session.items.count == 1
}
func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {
let dropLocation = session.location(in: view)
let operation: UIDropOperation
if interaction.view!.frame.contains(dropLocation) && session.localDragSession != nil {
operation = .move
} else {
operation = .cancel
}
return UIDropProposal(operation: operation)
}
func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession) {
session.loadObjects(ofClass: ViewContainer.self) { viewContainers in
guard let viewContainers = viewContainers as? [ViewContainer], let viewContainer = viewContainers.first else { return }
interaction.view!.addSubview(viewContainer.view)
self.setConstraintsInSuperView(forView: viewContainer.view)
}
}
}
