ios - UIDropInteractionDelegate performDrop 没有被调用？

我正在尝试构建一个简单的测试应用程序来学习拖放 API。对于这个问题，我只关注 Drop 场景。我有一个空白的 View Controller ，打开了 safari 应用程序(多任务处理)，然后我尝试将图像从谷歌拖到 View Controller 的 View 上。

我可以将图像从 safari 拖到我应用的 View Controller 中，但是当我放手时，下面的这个调用永远不会被调用:

func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession)

这是我的代码:

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)")
    }


}

上面的两个方法被调用，这个:

func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool

还有这个:

func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal

所以，我想弄清楚为什么会这样:

func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession)

永远不会被调用。

有什么建议吗？

---

Best Answer-推荐答案

就我而言，这是一个编程错误，我写了以下内容:

func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {

    return UIDropProposal(operation: .move)
}

但你不能总是使用move!仅当 session.allowsMo​​veOperation 为 true!

来自 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. [...]

来自 cancel documentation :

If the user attempts a drop activity, the drag operation is canceled and the dropInteraction(_:performDrop delegate method is not called.

关于ios - UIDropInteractionDelegate performDrop 没有被调用？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54817243/