UIDropInteractionDelegate.swift

extension ViewController: UIDropInteractionDelegate {
    
    func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {
        
        let location = session.location(in: self.view)
        let dropOperation: UIDropOperation?
        
        if session.canLoadObjects(ofClass: String.self) {
            
            if dropTextView.frame.contains(location) {
                dropOperation = .copy
            } else if  dropImageView.frame.contains(location) {
                dropOperation = .forbidden
            } else {
                dropOperation = .cancel
            }
        }
        else if session.canLoadObjects(ofClass: UIImage.self) {
            
            if dropImageView.frame.contains(location) {
                dropOperation = .copy
            } else if  dropTextView.frame.contains(location) {
                dropOperation = .forbidden
            } else {
                dropOperation = .cancel
            }
        }
        else {
            dropOperation = .cancel
        }
        
        return UIDropProposal(operation: dropOperation!)
    }
    
    func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession) {
        
        if session.canLoadObjects(ofClass: String.self) {
            
            session.loadObjects(ofClass: String.self) { (items) in
                let values = items as [String]
                self.dropTextView.text = values.last
                                                       
            }
        } else if session.canLoadObjects(ofClass: UIImage.self) {
            
            session.loadObjects(ofClass: UIImage.self) { (items) in
                let images = items as! [UIImage]
                self.dropImageView.image = images.last
                                                        
            }
        }
    }
}