调度队列后台线程更新在 iOS 12 上不起作用

Question

我有以下一段代码，在11.4.1上运行良好，但在12上失败

let background = DispatchQueue(label:"task")
var debugMeshNode = SCNNode()
let myKit = MyKit()
func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
self.background.async {
let node = self.myKit.extractNode(anchor:anchor)
self.debugMeshNode.addChildNode(node) // no node added on UI in iOS12
}
}
func session(_ session: ARSession, didUpdate frame: ARFrame) {
self.background.async {
self.myKit.process(frame: frame)
}
}

谁能在这里指出我的错误？

更新

如果我像这样在块中添加一个 print 语句，代码似乎有效，

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
self.background.async {
let node = self.myKit.extractNode(anchor:anchor)
self.debugMeshNode.addChildNode(node) // no node added on UI in iOS12
print("sample")
}
}

Answer 1

最初从这里开始，我使用了这个

func guaranteeMainThreadSynchronousExecution(_ block: () -> ()) {
if Thread.isMainThread {
block()
} else {
DispatchQueue.main.sync {
block()
}
}
}

并像这样更新了我的代码，

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
self.guaranteeMainThreadSynchronousExecution {
self.background.async {
let node = self.myKit.extractNode(anchor:anchor)
self.debugMeshNode.addChildNode(node) // no node added on UI in iOS12
}
}
}

然后它完美无缺地工作。希望这对某人有所帮助。