TextKit 1下NSTextView渲染异常（回车/退格问题）求解决方案

问题现象 #

使用TextKit 1构建的NSTextView存在以下渲染异常：

• 按下回车键时，最后一行出现卡顿且无法显示
• 按下退格键时，最后一行偶尔会出现临时重复的情况

复现代码（TextKit 1存在问题的实现） #

func bug() {
    let textContainer = NSTextContainer()
    textContainer.widthTracksTextView = true
    textContainer.heightTracksTextView = true

    let layoutManager = NSLayoutManager()
    let textStorage = NSTextStorage(string: "")

    layoutManager.addTextContainer(textContainer)
    textStorage.addLayoutManager(layoutManager)

    let textView = NSTextView(frame: .zero, textContainer: textContainer)
    textView.autoresizingMask = [.width, .height]

    // 触发bug的测试文本
    textView.string = "\naaaaa\nbbbbbb"
    textView.setSelectedRange(.init(location: 0, length: 0))

    let scrollView = NSScrollView()
    scrollView.documentView = textView
    scrollView.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(scrollView)

    NSLayoutConstraint.activate([
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        scrollView.topAnchor.constraint(equalTo: view.topAnchor),
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    ])
}

对比：TextKit 2无异常实现 #

测试发现切换到TextKit 2后，该问题完全消失，实现代码如下：

func textKit2NoBug() {
    let textView = NSTextView(usingTextLayoutManager: true)
    textView.autoresizingMask = [.width, .height]

    // 相同测试文本
    textView.string = "\naaaaa\nbbbbbb"
    textView.setSelectedRange(.init(location: 0, length: 0))

    let scrollView = NSScrollView()
    scrollView.documentView = textView
    scrollView.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(scrollView)

    NSLayoutConstraint.activate([
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        scrollView.topAnchor.constraint(equalTo: view.topAnchor),
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    ])
}

针对TextKit 1的解决方法 #

由于业务场景必须依赖TextKit 1，可通过以下几种方案修复：

方案1：禁用自动高度跟踪，手动管理文本容器高度 #

问题根源在于NSTextContainer的heightTracksTextView属性设为true时，文本视图高度计算在编辑操作时出现异常。关闭该属性后，通过监听文本变化动态调整容器高度：

func fixedBugWithManualHeight() {
    let textContainer = NSTextContainer()
    textContainer.widthTracksTextView = true
    textContainer.heightTracksTextView = false // 关闭自动高度跟踪

    let layoutManager = NSLayoutManager()
    let textStorage = NSTextStorage(string: "")

    layoutManager.addTextContainer(textContainer)
    textStorage.addLayoutManager(layoutManager)

    let textView = NSTextView(frame: .zero, textContainer: textContainer)
    textView.autoresizingMask = [.width, .height]
    textView.string = "\naaaaa\nbbbbbb"
    textView.setSelectedRange(.init(location: 0, length: 0))

    // 监听文本变化，更新容器高度
    textStorage.delegate = self
    
    let scrollView = NSScrollView()
    scrollView.documentView = textView
    scrollView.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(scrollView)

    NSLayoutConstraint.activate([
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        scrollView.topAnchor.constraint(equalTo: view.topAnchor),
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    ])
}

// MARK: - NSTextStorageDelegate
extension YourViewController: NSTextStorageDelegate {
    func textStorage(_ textStorage: NSTextStorage, didProcessEditing editedMask: NSTextStorageEditActions, range editedRange: NSRange, changeInLength delta: Int) {
        guard let textView = textStorage.layoutManagers.first?.textContainers.first?.textView else { return }
        let usedRect = textView.layoutManager?.usedRect(for: textView.textContainer!) ?? .zero
        let newHeight = usedRect.height + textView.textContainerInset.top + textView.textContainerInset.bottom
        textView.textContainer?.size.height = newHeight
        textView.invalidateIntrinsicContentSize()
    }
}

方案2：自定义TextView，强制编辑后刷新布局 #

如果必须保留heightTracksTextView = true，可通过重写编辑方法，在操作后强制触发布局刷新：

class FixedTextView: NSTextView {
    override func insertNewline(_ sender: Any?) {
        super.insertNewline(sender)
        // 强制刷新布局和显示
        layoutManager?.ensureLayout(for: textContainer!)
        setNeedsDisplay(bounds)
    }

    override func deleteBackward(_ sender: Any?) {
        super.deleteBackward(sender)
        // 强制刷新布局和显示
        layoutManager?.ensureLayout(for: textContainer!)
        setNeedsDisplay(bounds)
    }
}

// 使用自定义TextView替换原实现
func fixedBugWithForceRefresh() {
    let textContainer = NSTextContainer()
    textContainer.widthTracksTextView = true
    textContainer.heightTracksTextView = true

    let layoutManager = NSLayoutManager()
    let textStorage = NSTextStorage(string: "")

    layoutManager.addTextContainer(textContainer)
    textStorage.addLayoutManager(layoutManager)

    let textView = FixedTextView(frame: .zero, textContainer: textContainer)
    textView.autoresizingMask = [.width, .height]
    textView.string = "\naaaaa\nbbbbbb"
    textView.setSelectedRange(.init(location: 0, length: 0))

    let scrollView = NSScrollView()
    scrollView.documentView = textView
    scrollView.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(scrollView)

    NSLayoutConstraint.activate([
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        scrollView.topAnchor.constraint(equalTo: view.topAnchor),
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    ])
}

方案3：修正文本初始化方式 #

避免直接给textView.string赋值，改用NSTextStorage直接初始化文本，确保布局管理器正确处理初始排版：

func fixedBugWithProperInit() {
    let textContainer = NSTextContainer()
    textContainer.widthTracksTextView = true
    textContainer.heightTracksTextView = true

    let layoutManager = NSLayoutManager()
    let initialText = "\naaaaa\nbbbbbb"
    let textStorage = NSTextStorage(string: initialText) // 直接初始化文本

    layoutManager.addTextContainer(textContainer)
    textStorage.addLayoutManager(layoutManager)

    let textView = NSTextView(frame: .zero, textContainer: textContainer)
    textView.autoresizingMask = [.width, .height]
    textView.setSelectedRange(.init(location: 0, length: 0))

    let scrollView = NSScrollView()
    scrollView.documentView = textView
    scrollView.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(scrollView)

    NSLayoutConstraint.activate([
        scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        scrollView.topAnchor.constraint(equalTo: view.topAnchor),
        scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    ])
}

方案说明 #

• 方案1：从根源解决自动高度跟踪的布局冲突，是最稳定的解决方案
• 方案2：快速修复特定编辑操作下的渲染异常，适合临时应急
• 方案3：通过修正初始化逻辑，让TextKit 1正确处理文本排版，实现成本低

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