ARKit中ModelEntity点击变色及切换恢复原材质的问题

问题原因 #

你的代码中保存原始材质时，直接赋值了entity.model!.materials，而Material是引用类型，后续修改实体的材质（比如改成蓝色）时，保存到modelEntitiesMaterials里的“原始材质”会被同步修改。导致再次选中该实体时，先恢复的已经是被修改过的蓝色材质，再设置蓝色就看不到变化了。

解决方案 #

1. 保存材质的副本而非引用 #

需要为每个实体的原始材质创建独立副本，确保后续修改实体材质不会影响保存的原始数据。

2. 优化选中状态管理 #

直接跟踪当前选中的实体，避免每次遍历所有实体，提升性能的同时简化逻辑。

修改后的代码 #

替换状态跟踪变量 #

enum EntityState {
    case unselected
    case selected
    case correctName
    case wrongName
}

private var entitiesState: [String: EntityState] = [:]
private var modelEntities: [ModelEntity] = []
private var modelEntitiesMaterials: [String: [Material]] = [:]
// 新增：直接跟踪当前选中的实体，替代遍历查找
private var currentSelectedEntity: ModelEntity?

修改handleTap中的材质保存逻辑 #

@objc private func handleTap(sender: UITapGestureRecognizer) {
    let tapLocation = sender.location(in: arView)
    let result = arView.hitTest(tapLocation)
    
    guard let hitTest = result.first, hitTest.entity.name != "Ground Plane" else {
        selectEntity(withSelectedEntity: nil)
        return
    }
    
    guard let entity = hitTest.entity as? ModelEntity else { return }
    
    let keyExists = modelEntitiesMaterials[entity.name] != nil
    if !keyExists {
        // 保存材质的副本，避免引用导致原始材质被修改
        let originalMaterials = entity.model!.materials.map { material in
            if let simpleMat = material as? SimpleMaterial {
                // 手动复制SimpleMaterial的所有属性，创建新实例
                return SimpleMaterial(
                    color: simpleMat.color,
                    roughness: simpleMat.roughness,
                    isMetallic: simpleMat.isMetallic,
                    specularColor: simpleMat.specularColor,
                    clearcoat: simpleMat.clearcoat,
                    clearcoatRoughness: simpleMat.clearcoatRoughness,
                    normalTexture: simpleMat.normalTexture,
                    occlusionTexture: simpleMat.occlusionTexture,
                    emissiveColor: simpleMat.emissiveColor,
                    emissiveTexture: simpleMat.emissiveTexture,
                    transparency: simpleMat.transparency,
                    texture: simpleMat.texture
                )
            } else {
                // 其他材质类型使用NSObject的copy方法
                return material.copy() as! Material
            }
        }
        modelEntitiesMaterials[entity.name] = originalMaterials
    }
    
    selectEntity(withSelectedEntity: entity)
}

重写selectEntity函数 #

private func selectEntity(withSelectedEntity: ModelEntity?) {
    modelInformationView.isHidden = false
    
    // 先取消当前选中的实体，恢复其原始材质
    if let currentSelected = currentSelectedEntity {
        entitiesState[currentSelected.name] = .unselected
        if let originalMaterials = modelEntitiesMaterials[currentSelected.name] {
            currentSelected.model!.materials = originalMaterials
        }
        currentSelectedEntity = nil
    }
    
    guard let selectedEntity = withSelectedEntity else {
        modelInformationView.isHidden = true // 未选中任何实体时隐藏信息视图
        return
    }
    
    // 如果点击的是已选中的实体，直接取消（可选逻辑，根据需求调整）
    if selectedEntity == currentSelectedEntity {
        return
    }
    
    // 设置新的选中实体
    entitiesState[selectedEntity.name] = .selected
    currentSelectedEntity = selectedEntity
    // 应用选中状态的蓝色材质
    let selectedMaterial = SimpleMaterial(color: .link, isMetallic: false)
    selectedEntity.model?.materials[0] = selectedMaterial
}

可选：确保实体名称唯一 #

在placeObject中，为每个子实体设置唯一名称，避免modelEntitiesMaterials的键冲突：

if let geomChildrens = geomChildrens {
    for children in geomChildrens.children {
        let childModelEntity = children as! ModelEntity
        childModelEntity.collision = CollisionComponent(shapes: [ShapeResource.generateConvex(from: childModelEntity.model!.mesh)])
        // 设置唯一名称，避免键冲突
        childModelEntity.name = UUID().uuidString
        entitiesState[childModelEntity.name] = .unselected
        modelEntities.append(childModelEntity)
    }
}

说明 #

• 材质副本：通过手动复制SimpleMaterial属性或使用copy()方法，确保保存的原始材质与实体当前材质完全独立，不会被后续修改影响。
• 状态跟踪：直接维护currentSelectedEntity变量，避免每次遍历所有实体查找选中状态，代码更简洁，性能更优。

内容的提问来源于stack exchange，提问作者user13965197