Sprite Kit 的辅助功能（画外音）

Question

我正在尝试在具有固定棋盘的益智游戏中添加对旁白辅助功能的支持。但是，我无法让 UIAccessibilityElements 出现。

现在我在我的 SKScene 中覆盖 accessibilityElementAtIndex、accessibilityElementCount 和 indexOfAccessibilityElement。

他们正在返回一个可访问元素的数组，如下所示：

func loadAccessibleElements()
{
    self.isAccessibilityElement = false

    let pieces = getAllPieces()

    accessibleElements.removeAll(keepCapacity: false)
    for piece in pieces
    {
        let element = UIAccessibilityElement(accessibilityContainer: self.usableView!)

        element.accessibilityFrame = piece.getAccessibilityFrame()
        element.accessibilityLabel = piece.getText()
        element.accessibilityTraits = UIAccessibilityTraitButton
        accessibleElements.append(element)
    }
}

其中piece是SKSpriteNode的子类，getAccessibilityFrame被定义：

func getAccessibilityFrame() -> CGRect
{
    return parentView!.convertRect(frame, toView: nil)
}

现在一个（大小错误）accessibility 元素似乎出现在屏幕上的错误位置。

有人能指出我正确的方向吗？

非常感谢

编辑：
我已经尝试了一个 hack-ish 解决方法，方法是在 SKView 上放置一个 UIView，其中 UIButton 元素与 SKSpriteNodes 位于同一位置。但是，可访问性仍然不想工作。视图是这样加载的：

func loadAccessibilityView()
{
    view.isAccessibilityElement = false
    view.accessibilityElementsHidden = false
    skView.accessibilityElementsHidden = false
    let accessibleSubview = UIView(frame: view.frame)
    accessibleSubview.userInteractionEnabled = true
    accessibleSubview.isAccessibilityElement = false
    view.addSubview(accessibleSubview)
    view.bringSubviewToFront(accessibleSubview)

    let pieces = (skView.scene! as! GameScene).getAllPieces()
    for piece in pieces
    {
        let pieceButton = UIButton(frame: piece.getAccessibilityFrame())
        pieceButton.isAccessibilityElement = true
        pieceButton.accessibilityElementsHidden = false
        pieceButton.accessibilityTraits = UIAccessibilityTraitButton
        pieceButton.setTitle(piece.getText(), forState: UIControlState.Normal)
        pieceButton.setBackgroundImage(UIImage(named: "blue-button"), forState: UIControlState.Normal)
        pieceButton.alpha = 0.2
        pieceButton.accessibilityLabel = piece.getText()
        pieceButton.accessibilityFrame = pieceButton.frame
        pieceButton.addTarget(self, action: Selector("didTap:"), forControlEvents: UIControlEvents.TouchUpInside)
        accessibleSubview.addSubview(pieceButton)
    }

    UIAccessibilityPostNotification(UIAccessibilityScreenChangedNotification, nil)

}

按钮放置正确，但可访问性根本不起作用。似乎有什么东西阻止了它的工作。

Answer 1

我徒劳地搜索了有关如何使用 SpriteKit 在 Swift 中实现 VoiceOver 的描述，所以我终于想出了如何去做。下面是一些在添加到 SKScene 类时将 SKNode 转换为可访问按钮的工作代码：

// Add the following code to a scene where you want to make the SKNode variable named “leave” an accessible button
// leave must already be initialized and added as a child of the scene, or a child of other SKNodes in the scene
// screenHeight must already be defined as the height of the device screen, in points

// Accessibility

private var accessibleElements: [UIAccessibilityElement] = []

private func nodeToDevicePointsFrame(node: SKNode) -> CGRect {

    // first convert from frame in SKNode to frame in SKScene's coordinates

    var sceneFrame = node.frame
    sceneFrame.origin = node.scene!.convertPoint(node.frame.origin, fromNode: node.parent!)

    // convert frame from SKScene coordinates to device points
    // sprite kit scene origin is in lower left, accessibility device screen origin is at upper left
    // assumes scene is initialized using SKSceneScaleMode.Fill using dimensions same as device points

    var deviceFrame = sceneFrame
    deviceFrame.origin.y = CGFloat(screenHeight-1) - (sceneFrame.origin.y + sceneFrame.size.height)
    return deviceFrame
}

private func initAccessibility() {
    if accessibleElements.count == 0 {
        let accessibleLeave = UIAccessibilityElement(accessibilityContainer: self.view!)
        accessibleLeave.accessibilityFrame = nodeToDevicePointsFrame(leave)
        accessibleLeave.accessibilityTraits = UIAccessibilityTraitButton
        accessibleLeave.accessibilityLabel = “leave” // the accessible name of the button
        accessibleElements.append(accessibleLeave)
    }
}
override func didMoveToView(view: SKView) {
    self.isAccessibilityElement = false
    leave.isAccessibilityElement = true
}

override func willMoveFromView(view: SKView) {
    accessibleElements = []
}

override func accessibilityElementCount() -> Int {
    initAccessibility()
    return accessibleElements.count
}

override func accessibilityElementAtIndex(index: Int) -> AnyObject? {
    initAccessibility()
    if (index < accessibleElements.count) {
        return accessibleElements[index] as AnyObject
    } else {
        return nil
    }
}

override func indexOfAccessibilityElement(element: AnyObject) -> Int {
    initAccessibility()
    return accessibleElements.indexOf(element as! UIAccessibilityElement)!
}

Answer 2

辅助功能框架是在固定的物理屏幕坐标中定义的，而不是 UIView 坐标，并且它们之间的转换有点棘手。

当设备处于横向模式时，设备原点是屏幕的左下角，X 向上。

这是一个痛苦的转换，我不知道为什么苹果会这样做。