swift - macOS Swift 主从委托(delegate)/协议(protocol)不起作用

Question

这道题一定很简单，但我是新手。我有一个 splitView，我试图将其作为主从关系进行管理。用户单击 Master 中的 OutlineView 项，这会触发更新 Detail 端 PopUp 按钮内容的需要。我已经尝试了几个较大代码中的安排测试，从中提取了下面的代码(参见下面代码中标记的测试 1、测试 2、测试 3、测试 4。失败的是测试 3，它失败是因为 displayListPopUP当它被委托(delegate)调用时，它在协议(protocol)函数中为 nil，尽管当类 DetailViewController 最初使用相同的指令加载 PopUp 时它不是 nil。如何修复 TEST 3？

import Cocoa

var displayList: [String] = []

class MasterViewController: NSViewController {

    weak var delegate: detailViewControllerDelegate?
    let detailViewController = DetailViewController()

    override func viewDidLoad() {
        super.viewDidLoad()
        displayList = ["Problem(s) in Selected Category","EM3", "EM4"]        
        self.delegate = detailViewController as          detailViewControllerDelegate

    // TEST 1---THIS WORKS (Bingo is printed)
        delegate?.testPrint(val: "Bingo")
}

extension MasterViewController: NSOutlineViewDelegate {

    func outlineViewSelectionDidChange(_ notification: Notification){

        displayList = ["Problem(s) in Selected Category","EM1", "EM2"]

    // TEST 2---THIS WORKS (Bingo 2 is printed)
        delegate?.testPrint(val: "Bingo 2")

    // TEST 3---THIS DOESN'T WORK (displayListPopUP is nil)
        delegate?.loadListPopUP(list: displayList)
    }
}

protocol detailViewControllerDelegate: class {
    func testPrint(val: String)
    func loadListPopUP(list: [String])
}


class DetailViewController: NSViewController, detailViewControllerDelegate     {

//I CHECK, XCODE SAYS THIS OUTLET IS ACTIVE
    @IBOutlet weak var displayListPopUP: NSPopUpButton!

    override func viewDidLoad() {
        super.viewDidLoad()

    //TEST 4---THIS WORKS (PopUp button is loaded correctly)
        displayListPopUP.removeAllItems()
        displayListPopUP.addItems(withTitles: displayList)
    }

    func testPrint(val: String){
        print(val)
    }

    func loadListPopUP(list: [String]){
    //THIS DOES NOT WORK.  displayListPopUP is nil when called from delegate
        displayListPopUP.removeAllItems()
        displayListPopUP.addItems(withTitles: list)
    }

Answer 1

这似乎解决了问题:

var detailViewController = DetailViewController()
weak var delegate: detailViewControllerDelegate?

override func viewDidLoad() {
    super.viewDidLoad()

...

detailViewController = 

self.storyboard?.instantiateController(withIdentifier: "detailVC") 作为! NSViewController 作为!细节 View Controller

 // This is a trick to force the detailViewController to load its hierarchy     view, icluding displayListPopUP

    _ = detailViewController.view

...

确实，xcode 确实显示了我的 PopUp 的事件导出。 DetailViewController 的初始显示显然是由 macOS 管理的，它有自己的 View 实例化。因此测试 4 确实有效。

创建主从关系显然需要我的 DetailViewController 的新实例化。因为我使用的是 Storyboard，nibs 和 xibs，如果它们存在的话，是眼不见心不烦的。因此，@OOper 的实例化必须替换为显示的实例化。但是，他是对的，实例化不会加载 View 层次结构。那时测试 3 将失败，因为 displayPopUP 仍然为零。 View 层次结构在第一次引用 View 后加载，显示的虚拟调用强制加载层次结构，displayPopUP 现在处于事件状态。测试 3 现在成功了。