拖放的自定义视图 [英] Custom view for Drag and Drop

问题描述

我已经设置了我的 UITableView 以使用新的拖放 API.

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
}

现在，我实现了以下方法，以便能够为 d&d 使用自定义视图.

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)
}

然而，这个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?

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

推荐答案

创建UIDragItem时必须设置previewProvider属性.

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)
}

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

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