无法使用 segue 将值从 FirstVC 传递到 SecondVC

Question

我有两个 ViewControllers 通过 Show segue 连接。我需要将 NSSlider 的值从 ViewController 传递到 SecondViewCotroller。

因此，在 ViewController 中移动滑块会在 SecondViewController 中更新变量。

如何更新 imagesQty 变量的值？

// FIRST VIEW CONTROLLER

import Cocoa

class ViewController: NSViewController {

    @IBOutlet weak var slider: NSSlider!
    @IBOutlet weak var photosLabel: NSTextField!

    @IBAction func segueData(_ sender: NSSlider) {
        photosLabel.stringValue = String(slider.intValue) + " photos"
        self.performSegue(withIdentifier: NSStoryboardSegue.Identifier(rawValue: "SegueIdentifierForSecondVC"), sender: slider)
    }

    func prepare(for segue: NSStoryboardSegue, sender: NSSlider?) {
        if segue.identifier!.rawValue == "SegueIdentifierForSecondVC" {
            if let secondViewController =
            segue.destinationController as? SecondViewController {
                secondViewController.imagesQty = slider.integerValue
            }
        }
    }
}

和

// SECOND VIEW CONTROLLER

import Cocoa

class SecondViewController: NSViewController {

    var imagesQty = 30  

    override func viewWillAppear() {

    super.viewWillAppear()
    self.view.wantsLayer = true

    print("viewWillAppear – Qty:\(imagesQty)")

    //let arrayOfViews: [NSImageView] = [view01...view12]

    let url = URL(fileURLWithPath: NSHomeDirectory()).appendingPathComponent("Desktop/ArrayOfElements")
    do {
        let fileURLs = try FileManager.default.contentsOfDirectory(at: url, includingPropertiesForKeys: nil, options: [.skipsHiddenFiles]).reversed()
        let photos = fileURLs.filter { [=11=].pathExtension == "jpg" }

        for view in arrayOfViews {
            //"imagesQty" is here
            let i = Int(arc4random_uniform(UInt32(imagesQty-1)))
            let image = NSImage(data: try Data(contentsOf: photos[i]))
            view.image = image
            view.imageScaling = .scaleNone
        }
    } catch {
        print(error)
    }
}

Answer 1

您无法更改该值，因为 var 是在函数中定义的，而不是在 class 中定义的。

将您的变量设置为 class 属性它应该可以工作。

class SecondViewController: UIViewController {

var imagesQty: Int = 30

...

}

Answer 2

首先，NSStoryboardSegue.Identifier 的目的和好处是创建一个能够避免文字的扩展。

extension NSStoryboardSegue.Identifier {
    static let secondVC = NSStoryboardSegue.Identifier("SegueIdentifierForSecondVC")
}

那你可以写

self.performSegue(withIdentifier: .secondVC, sender: slider)

和

if segue.identifier! == .secondVC { ...

发生此错误是因为 imagesQty 是在 viewWillAppear 中声明的，而不是在 class 的顶层声明的。

改为

class SecondViewController: NSViewController {

    var imagesQty = 30 // Int is inferred

    // override func viewWillAppear() {
    //     super.viewWillAppear()
    // }
}

还有一个错误：prepare(for segue的签名是错误的。必须是

func prepare(for segue: NSStoryboardSegue, sender: Any?) {

无法使用 segue 将值从 FirstVC 传递到 SecondVC

Can't pass value from FirstVC to SecondVC using segue

macos

nsslider

segue

swift

swift4