如何以编程方式触发UIContextMenuInteraction上下文菜单？

Question

我已经将UIButton设置为UINavigationController中的UIViewController中的rightBarButtonItem，并将iOS13上下文菜单与其相关联。

长时间按下按钮将显示预期的上下文菜单。

是否也可以通过点击按钮来显示上下文菜单(例如，为.touchUpInside事件添加一个目标)？

按钮/barButtonItem设置如下：

let button = UIButton(type: .system)
button.setImage(UIImage(systemName: "plus"), for: .normal)

let barButton = UIBarButtonItem(customView: button)
self.navigationItem.rightBarButtonItem = barButton

let interaction = UIContextMenuInteraction(delegate: self)
button.addInteraction(interaction)

上下文菜单的定义如下：

extension ViewController: UIContextMenuInteractionDelegate {
    func contextMenuInteraction(_ interaction: UIContextMenuInteraction, configurationForMenuAtLocation location: CGPoint) -> UIContextMenuConfiguration? {
        return UIContextMenuConfiguration(identifier: nil, previewProvider: nil) { suggestedActions in
            let importAction = UIAction(title: "Import", image: UIImage(systemName: "folder")) { action in }
            let createAction = UIAction(title: "Create", image: UIImage(systemName: "square.and.pencil")) { action in }
            return UIMenu(title: "", children: [importAction, createAction])
        }
    }
}

Answer 1

根据设计，当适当的手势(用力触摸或长按压)发生时，系统会自动显示上下文菜单。你不能手动显示。

来自文档

一个上下文菜单交互对象跟踪支持3D触摸的设备上的Force 手势，以及不支持它的设备上的长按手势。 UIKit 管理所有与菜单相关的交互，并将选定的操作(如果有的话)报告给应用程序。

更新

尽管仍然无法在iOS 14中手动显示上下文菜单，但现在可以将我们为上下文菜单创建的UIMenu显示为下拉菜单。有关如何在@Lobo的回答 14上执行此操作，请查看iOS。

Answer 2

iOS 14

iOS 14 (first )现在支持所需的功能。有了下面的代码，UIBarButtonItem上的点击将立即显示菜单(也避免了调用UIContextMenuInteraction造成的模糊背景)：

override func viewDidLoad() {
    super.viewDidLoad()
    
    let importAction = UIAction(title: "Import", image: UIImage(systemName: "folder")) { action in }
    let createAction = UIAction(title: "Create", image: UIImage(systemName: "square.and.pencil")) { action in }
    
    let menuBarButton = UIBarButtonItem(
        title: "Add",
        image: UIImage(systemName:"plus"),
        primaryAction: nil,
        menu: UIMenu(title: "", children: [importAction, createAction])
    )
    
    self.navigationItem.rightBarButtonItem = menuBarButton
}

该功能是通过不提供primaryAction来实现的。

您可以使用UIButton实现同样的效果。在这种情况下，您需要设置

button.showsMenuAsPrimaryAction = true

UIButton的完整代码如下所示：

override func viewDidLoad() {
    super.viewDidLoad()
   
    let button = UIButton(type: .system)
    button.setImage(UIImage(systemName: "plus"), for: .normal)
    button.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(button)
    
    NSLayoutConstraint.activate([
        button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        button.centerYAnchor.constraint(equalTo: view.centerYAnchor)
    ])
    
    let importAction = UIAction(title: "Import", image: UIImage(systemName: "folder")) { action in }
    let createAction = UIAction(title: "Create", image: UIImage(systemName: "square.and.pencil")) { action in }
    
    let items = [importAction, createAction]
    
    button.menu = UIMenu(title: "Add", children: items)
    button.showsMenuAsPrimaryAction = true
}

Answer 3

使用私有API可以完成这项工作。

@objc
func buttonTapped() {
    // _presentMenuAtLocation:
    guard let interaction = imageView.interactions.first,
          let data = Data(base64Encoded: "X3ByZXNlbnRNZW51QXRMb2NhdGlvbjo="),
          let str = String(data: data, encoding: .utf8)
    else {
        return
    }
    let selector = NSSelectorFromString(str)
    guard interaction.responds(to: selector) else {
        return
    }
    interaction.perform(selector, with: CGPoint.zero)
}