Custom view for Drag and Drop

问题

I have set up my UITableView to use the new Drag and Drop APIs.

if #available(iOS 11, *) {
    self.tableView.dragDelegate = self
    self.tableView.dropDelegate = self
    self.tableView.dragInteractionEnabled = true
    navigationController?.navigationBar.prefersLargeTitles = false
}

Now, I implemented the method below to be able to use custom views for the d&d.

@available(iOS 11.0, *)
func dragInteraction(_ interaction: UIDragInteraction, previewForLifting item: UIDragItem, session: UIDragSession) -> UITargetedDragPreview? {
    print("Custom Preview method called!")
    let test = UITextView.init(frame: CGRect.init(x: 0, y: 0, width: 200, height: 200))
    test.text = "sfgshshsfhshshfshsfh"
    let dragView = interaction.view!
    let dragPoint = session.location(in: dragView)
    let target = UIDragPreviewTarget(container: dragView, center: dragPoint)
    return UITargetedDragPreview(view: test, parameters:UIDragPreviewParameters(), target:target)
}

However, this method never gets called. I never see the print() or my custom view. Any ideas as to what I'm doing wrong?

回答1:

You have to set previewProvider property when creating the UIDragItem.

let dragItem = UIDragItem(...)
dragItem.previewProvider = {
    print("Custom Preview method called!")
    let test = UITextView.init(frame: CGRect.init(x: 0, y: 0, width: 200, height: 200))
    test.text = "sfgshshsfhshshfshsfh"
    return UIDragPreview(view: test)
}

See: https://developer.apple.com/documentation/uikit/uidragitem/2890972-previewprovider?language=objc

回答2:

Are you using an iPhone? I am not certain it is currently working for customer UIViewController as of November 25, 2017 based on the following:

I downloaded the Apple sample project for drag-and-drop on an iPad
I added a breakpoint in dragInteraction and confirmed I could reach it
I modified the target to be a universal app (i.e. iPhone, too)
I ran on an iPhone 8 device and did not reach the breakpoint

As further suggestion, there is a property named dragInteractionEnabled for both UITableViewController and UICollectionViewController. For iPhone devices, the property is defaulted to false and, more importantly, the property is not even defined higher in UIViewController.

来源：https://stackoverflow.com/questions/45140854/custom-view-for-drag-and-drop

标签

ios

uitableview