swift - 重写 NSTreeController 的排列对象

Question

在我的项目中，NSTreeController 绑定(bind)到 NSOutlineView( cocoa 绑定(bind))。由于某种原因我无法使用NSPredicate从Core Data中过滤数据。因此，我尝试覆盖 NSTreeController 的 arrangedObjects，但覆盖的 arrangedObjects 甚至还没有被解雇。 (我在其中设置了一个调试断点。)代码编译良好，并且我已经将实例更改为我的 CleanTreeController。我只找到an unanswered question asked a decade ago在邮件列表中。

// Subclass of NSTreeController
class CleanTreeController: NSTreeController {
    init() {
        // This gets called.
        super.init(content: nil)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }

    override var arrangedObjects: Any {
        let oldArranged = super.arrangedObjects

        let selector = NSSelectorFromString("childNodes")

        guard let oldChildren = (oldArranged as! NSObject)
                            .perform(selector).takeUnretainedValue() as? [NSTreeNode]
        else
        {
            return oldArranged
        }

        let children = oldChildren.filter { (treeNode) in
            //... do some filtering
        }

        return TreeNodeProxy(with: children)
    }
}

// Homemade NSTreeNodeProxy
class TreeNodeProxy : NSObject {

    fileprivate var rootNode : NSTreeNode

    init(with children : [NSTreeNode]) {
        self.rootNode = NSTreeNode()
        self.rootNode.mutableChildren.addObjects(from: children)
    }

    @objc(childNodes)
    var children: [NSTreeNode]? {
        return rootNode.children
    }

    @objc(descendantNodeAtIndexPath:)
    func descendant(at indexPath: IndexPath) -> NSTreeNode? {
        return rootNode.descendant(at: indexPath)
    }
}

我发现了

The value returned by NSTreeController's arrangedObjects method is opaque. You should only observe this property to determine that a change has occurred.

在 doc 。那么，NSOutineView 如何在不(直接)读取 arrangedObjects 的情况下使用它呢？

Answer 1

在 xib 或代码中设置 NSTreeController 的 fetchPredicate。