启用usesAutomaticRowHeights的NSOutlineView出现重入警告及异常求助

警告含义 #

WARNING: Application performed a reentrant operation in its NSTableView delegate. 这个警告表示：在NSOutlineView（继承自NSTableView）的委托/数据源方法执行过程中，应用触发了会再次调用委托方法的操作，也就是出现了重入。这种重入会破坏视图布局计算的正常流程，直接导致行重叠、点击无响应等UI异常，尤其在启用自动行高时，布局计算对委托方法的调用顺序稳定性要求更高。

问题触发原因 #

你的场景里，核心诱因是初始化流程中调用时机不当：

• 在loadView里，调用outlineView.reloadData()后立刻执行expandItem(data)展开所有节点。当启用自动行高+实现isGroupItem方法时，展开操作会触发NSOutlineView重新计算行高，而这个计算过程会再次调用委托/数据源方法，和当前未完成的初始化流程形成重入。
• 即便isGroupItem返回false，只要实现了这个方法，NSOutlineView在自动行高计算时会额外执行分组相关的逻辑检查，大幅提升了重入的概率。

解决方案 #

方案1：延迟展开操作 #

把节点展开操作延迟到视图初始化和布局完成后执行，避免在委托/数据源的执行周期内触发重入。可以用主队列异步调用，或者移到viewDidAppear方法中：

方式A：主队列延迟调用

修改loadView中的代码：

outlineView.reloadData()
// 延迟到主队列下一轮循环执行，避开初始化时的委托调用周期
DispatchQueue.main.async { [weak self] in
    guard let self = self else { return }
    self.expandItem(self.data)
}

方式B：移到viewDidAppear

override func loadView() {
    outlineView = NSOutlineView(dataSource: self, delegate: self, columns: [
        NSTableColumn(identifier: "", title: "", width: 400),
        NSTableColumn(identifier: "", title: "", width: 100)
    ])
    let scrollView = NSScrollView(documentView: outlineView)
    view = NSView()
    view.addSubview(scrollView)
    NSLayoutConstraint.constrain(scrollView, toMarginsOf: view, edgeInsets: .zero)
    outlineView.reloadData()
}

override func viewDidAppear() {
    super.viewDidAppear()
    expandItem(data)
}

方案2：移除不必要的isGroupItem实现 #

如果你的场景不需要分组功能，直接删除outlineView(_:isGroupItem:)方法即可。NSOutlineView默认会将所有项视为非分组项，这样能跳过分组相关的额外布局检查，从根源减少重入可能。

完整修正代码 #

import Cocoa

class ViewController: NSViewController, NSOutlineViewDataSource, NSOutlineViewDelegate {
    
    var outlineView: NSOutlineView!
    
    let data: Any = [[[[[[[0], [0, [0,0,0]]], [0, [0, [0,0]],0,0,0,0,0]]], [[[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]],1]]]]

    override func loadView() {
        outlineView = NSOutlineView(dataSource: self, delegate: self, columns: [
            NSTableColumn(identifier: "", title: "", width: 400),
            NSTableColumn(identifier: "", title: "", width: 100)
        ])
        let scrollView = NSScrollView(documentView: outlineView)
        view = NSView()
        view.addSubview(scrollView)
        NSLayoutConstraint.constrain(scrollView, toMarginsOf: view, edgeInsets: .zero)
        outlineView.reloadData()
        // 延迟展开操作
        DispatchQueue.main.async { [weak self] in
            guard let self = self else { return }
            self.expandItem(self.data)
        }
    }

    private func expandItem(_ item: Any) {
        if let item = item as? [Any] {
            outlineView.expandItem(item)
            for content in item {
                expandItem(content)
            }
        }
    }
    
    func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        return item is [Any]
    }

    func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
        return ((item ?? data) as! [Any]).count
    }
    
    func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
        return ((item ?? data) as! [Any])[index]
    }
    
    func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
        let view = NSTableCellView()
        return view
    }
}

// 以下扩展代码保持不变
extension NSOutlineView {
    convenience init(dataSource: NSOutlineViewDataSource, delegate: NSOutlineViewDelegate, columns: [NSTableColumn]) {
        self.init()
        self.dataSource = dataSource
        self.delegate = delegate
        for column in columns {
            addTableColumn(column)
        }
        usesAutomaticRowHeights = true
    }
}

extension NSTableColumn {
    convenience init(identifier: String, title: String, width: Double, minWidth: Double = 10, maxWidth: Double = .infinity) {
        self.init(identifier: NSUserInterfaceItemIdentifier(identifier))
        self.title = title
        self.width = width
        self.minWidth = minWidth
        self.maxWidth = maxWidth
    }
}

extension NSLayoutConstraint {
    static func constrain(_ view: NSView, toMarginsOf superview: NSView, edgeInsets: NSEdgeInsets) {
        NSLayoutConstraint.activate([
            NSLayoutConstraint(item: view, attribute: .top, relatedBy: .equal, toItem: superview, attribute: .top, multiplier: 1, constant: edgeInsets.top),
            NSLayoutConstraint(item: view, attribute: .left, relatedBy: .equal, toItem: superview, attribute: .left, multiplier: 1, constant: edgeInsets.left),
            NSLayoutConstraint(item: superview, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: edgeInsets.bottom),
            NSLayoutConstraint(item: superview, attribute: .right, relatedBy: .equal, toItem: view, attribute: .right, multiplier: 1, constant: edgeInsets.right)
        ])
    }
}

extension NSEdgeInsets {
    static var zero: NSEdgeInsets {
        return NSEdgeInsets(all: 0)
    }
    
    init(all: Double) {
        self.init(top: all, left: all, bottom: all, right: all)
    }
}

extension NSScrollView {
    convenience init(documentView: NSView) {
        self.init()
        self.documentView = documentView
        hasVerticalScroller = true
        translatesAutoresizingMaskIntoConstraints = false
    }
}

内容的提问来源于stack exchange，提问作者Nickkk