问题
I am trying to build a simple test app to learn Drag and Drop APIs. For this question I am focusing only on the Drop scenario. I have a blank View Controller, with the safari app open (multitasking) I then try to drag an image from google onto the View Controller's view.
I can drag the image from safari to my app's View Controller, but when I let go, this call below is never called:
func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession)
This is my code:
class EditTestVC: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
view.addInteraction(UIDropInteraction(delegate: self))
}
}
extension EditTestVC:UIDropInteractionDelegate {
func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool { // 1
print("canHandle session: \(session)")
return true
// return session.canLoadObjects(ofClass: UIImage.self)
}
func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal { // 2
print("sessionDidUpdate session: \(session)")
return UIDropProposal(operation: .copy)
}
func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession) {
print("performDrop session: \(session)")
}
}
The top two methods are called, this one:
func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool
and this one:
func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal
So, I am trying to figure out why this one:
func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession)
is never called.
Any suggestion?
回答1:
I just tested your code and all methods are getting called. It must be a glitch.
Troubleshooting steps:
Delete app -> Restart the simulator -> Clean build folder -> Rebuild -> Run. You can also try running in different simulator first to save time.
回答2:
@bhaumik suggestion worked. Xcode for some reason was not working as expected. I deep cleaned and restarted Xcode. It now works.
回答3:
In my case it was a programming error where I've written the following:
func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {
return UIDropProposal(operation: .move)
}
But you cannot always use move! Only if session.allowsMoveOperation is true!
From the move documentation:
You may use this operation only if the drop session's allowsMoveOperation property is true; otherwise, it's treated as a UIDropOperation.cancel operation. [...]
From the cancel documentation:
If the user attempts a drop activity, the drag operation is canceled and the dropInteraction(_:performDrop:) delegate method is not called.
回答4:
I faced this issue and what i found was i did not set dropdelegate to self in collectionView.
collectionView.dropDelegate = self
After adding above line in viewDidLoad it worked!!
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dragDelegate = self
collectionView.dropDelegate = self
collectionView.dragInteractionEnabled = true
collectionView.reorderingCadence = .fast
// Do any additional setup after loading the view, typically from a nib.
}
来源：https://stackoverflow.com/questions/54817243/uidropinteractiondelegate-performdrop-not-called