ios - 设置 SCNNode 几何属性

Question

我有一个 SCNNode，我正在使用此方法将 .dae 文件中的几何图形应用到它:

func addNode(gridPosition: SCNVector3, row: Int, gamePlaneHeight: Float, sceneArray: [ObjectInfo]) -> SCNNode {

    // Create a material using the model_texture.tga image
    let carMaterial = SCNMaterial()
    carMaterial.diffuse.contents = UIImage(named: "assets.scnassets/Textures/model_texture.tga")
    carMaterial.locksAmbientWithDiffuse = false

    // Create a clone of the Car node of the carScene - you need a clone because you need to add many cars
    var carNode: SCNNode!
    let randomNumb = AppDelegate().randRange(0, upper: sceneArray.count - 1)
    let selectedObject = sceneArray[randomNumb]
    carNode = selectedObject.objectscene.rootNode.childNodeWithName(selectedObject.objectname, recursively: false)!.clone() as SCNNode

    carNode.scale = SCNVector3(0.5, 0.5, AppDelegate().randomBetweenNumbers(0.8, secondNum: 2.2))
    carNode.name = selectedObject.objectname
    carNode.position = gridPosition
    carNode.position.y = carNode.position.y + gamePlaneHeight

    // Set the material
    carNode.geometry?.firstMaterial = carMaterial

    return carNode
}

该方法大部分时间有效，但偶尔会在线上崩溃

carNode.geometry?.firstMaterial = carMaterial

错误

fatal error: unexpectedly found nil while unwrapping an Optional value
warning: could not load any Objective-C class information from the dyld shared cache. This will significantly reduce the quality of type information available.

我不明白为什么，因为大多数时候它都有效。

Answer 1

carNode 是从 selectedObject.objectname 构建的。如果场景中不存在 selectedObject.objectname，则 childNodeWithName 将返回 nil。因为 carNode 是一个隐式展开的可选项，Swift 将尝试展开 nil 并崩溃。

您应该使 carNode 可选(var carNode: SCNNode?)或添加测试，例如 if carNode == nil { ... } 并尝试调试您的输入 (selectedObject) 是什么以及它为什么不正确。