在UIScreenEdgePanGestureRecognizer中，'edges = UIRectEdge.all'的用例是什么？

Question

来自Apple API（见下文）：

1. UIScreenEdgePanGestureRecognizer具有类型的属性边 UIRectEdge

2. UIRectEdge具有以下属性：[top，left，right，bottom，all]

我认为UIRectEdge.all的目的是包括所有其他四个方向。 但是根据我的测试（见下文），.all根本没有检测到任何方向。

//  UIScreenEdgePanGestureRecognizer.h
//  Copyright (c) 2012-2015 Apple Inc. All rights reserved.
//

/*! This subclass of UIPanGestureRecognizer only recognizes if the user slides their finger
in from the bezel on the specified edge. */
    @available(iOS 7.0, *)
    open class UIScreenEdgePanGestureRecognizer : UIPanGestureRecognizer {

    open var edges: UIRectEdge //< The edges on which this gesture recognizes, relative to the current interface orientation
}

官方UIRectEdge结构：

public struct UIRectEdge : OptionSet {
    public init(rawValue: UInt)

    public static var top: UIRectEdge { get }
    public static var left: UIRectEdge { get }
    public static var bottom: UIRectEdge { get }
    public static var right: UIRectEdge { get }
    public static var all: UIRectEdge { get }
}

但是当我们设置边缘时，边缘检测无法检测到“任何”边缘方向= UIRectEdge.all

即。什么都不会被发现 （而不是4个方向检测，没有检测到方向） 使用此代码时：

let myEdgePan = UIScreenEdgePanGestureRecognizer()
myEdgePan.edges = UIRectEdge.all
myEdgePan.maximumNumberOfTouches = 2
myEdgePan.minimumNumberOfTouches = 1
myEdgePan.addTarget(self, action: #selector(ViewController.myEdgePanned(_:)))
self.view.addGestureRecognizer(coolEdgePan)

相反，我需要以下解决方法来检测所有4个边缘平移方向：

let edges : [UIRectEdge] = [.left, .right, .top, .bottom]

for edge in edges {
    let myEdgePan = UIScreenEdgePanGestureRecognizer()
    myEdgePan.edges = edge
    myEdgePan.maximumNumberOfTouches = 2
    myEdgePan.minimumNumberOfTouches = 1
    myEdgePan.addTarget(self, action: #selector(ViewController.myEdgePanned(_:)))
    self.view.addGestureRecognizer(coolEdgePan)
    }

有人知道'UIRectEdge.all'的用例是什么？