拖放的自定义视图

Question

我已经设置UITableView为使用新的拖放 API。

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

现在，我实现了下面的方法，以便能够为 d&d 使用自定义视图。

@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)
}

但是，此方法永远不会被调用。我从来没有看到print()或我的自定义视图。关于我做错了什么的任何想法？

Answer 1

previewProvider创建 UIDragItem 时必须设置属性。

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)
}

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