虽然我不知道原因，但它起作用了：

NSApp.mainWindow?.resignMain()
NSApp.mainWindow?.becomeMain()

下面是完整的代码：

class MyViewController: NSViewController {
    private lazy var searchField: NSSearchField = {
        let searchField = NSSearchField(string: "")

        if let searchButtonCell = searchField.searchButtonCell {
            searchButtonCell.setButtonType(.toggle)
            let filterImage = #imageLiteral(resourceName: "filter")
            searchButtonCell.image = filterImage.tinted(with: .systemGray)
            searchButtonCell.alternateImage = filterImage.tinted(with: .systemBlue)
        }
        searchField.focusRingType = .none
        searchField.bezelStyle = .roundedBezel
        searchField.delegate = self

        return searchField
    }()

    ...
}

extension MyViewController: NSSearchFieldDelegate {
    func searchFieldDidStartSearching(_ sender: NSSearchField) {
        sender.searchable = true
    }

    func searchFieldDidEndSearching(_ sender: NSSearchField) {
        sender.searchable = false
    }
}

extension NSSearchField {
    var searchButtonCell: NSButtonCell? {
        (self.cell as? NSSearchFieldCell)?.searchButtonCell
    }

    var searchable: Bool {
        get {
            self.searchButtonCell?.state == .on
        }

        set {
            self.searchButtonCell?.state = newValue ? .on : .off
            self.refreshSearchIcon()
        }
    }

    private func refreshSearchIcon() {
        NSApp.mainWindow?.resignMain()
        NSApp.mainWindow?.becomeMain()
    }
}

extension NSImage {
    func tinted(with color: NSColor) -> NSImage? {
        guard let image = self.copy() as? NSImage else { return nil }
        image.lockFocus()
        color.set()
        NSRect(origin: NSZeroPoint, size: self.size).fill(using: .sourceAtop)
        image.unlockFocus()
        image.isTemplate = false
        return image
    }
}

我也遇到了同样的问题。一个简单的覆盖为我解决了这个问题

extension NSSearchField{
    open override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)
    }
}

正如你所看到的，当你点击视图内部时，它仍然聚焦在搜索文本字段上（就像你在它下面点击后仍然可以输入一样）。由于当它失去焦点时，改变图像是打开的，你应该检查一下你是否点击了文本字段的外部。

通过子类化 NSSearchFieldCell 并将该类分配给字段的单元格来解决问题。

你甚至不需要子类化NSSearchFieldCell，当你从代码中创建你的NSSearchField时，你可以这样做：

if let searchFieldCell = searchField.cell as? NSSearchFieldCell {
    let image = NSImage(named: "YourImageName")
    searchFieldCell.searchButtonCell?.image = image
    searchFieldCell.searchButtonCell?.alternateImage = image // Optionally
}

如果你使用的是故事板，你可以在@IBOutlet的didSet中做同样的事情。