ios - appDelegate 中的委托(delegate)函数不会更改导航栏颜色

Question

Xcode 11.3.1，iOS 13

如果应用程序中存在特定条件，我将尝试更改所有 View Controller 上导航栏的颜色。使用 AppDelegate 中的委托(delegate)函数，使用最初设置全局颜色的相同代码似乎合乎逻辑。

这是我的代码:

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    var myColor : UIColor?

    let themeColorUS = UIColor(red: 0.991, green: 0.621, blue: 0.022, alpha: 1.00)
    let themeColorCanada = UIColor(red: 0.001, green: 0.686, blue: 0.000, alpha: 1.00)
    let themeColorGeneral = UIColor(red: 0.000, green: 0.954, blue: 0.969, alpha: 1.00)

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        UserDefaults.standard.setValue(false, forKey: "_UIConstraintBasedLayoutLogUnsatisfiable")

        setBarColors(issuingFlag: "General")

        return true
    }

...

func setBarColors(issuingFlag:String) {

    if issuingFlag == "US" {
        myColor = themeColorUS
    }else if issuingFlag == "Canada"{
        myColor = themeColorCanada
    }else{
        myColor = .magenta
    }

    print("issuingFlag == \(issuingFlag)")

    if #available(iOS 13.0, *) {

        let appearance = UINavigationBarAppearance()
        appearance.backgroundColor = myColor
        appearance.titleTextAttributes = [.foregroundColor: UIColor.black]
        appearance.largeTitleTextAttributes = [.foregroundColor: UIColor.black]

        UINavigationBar.appearance().tintColor = .black
        UINavigationBar.appearance().standardAppearance = appearance
        UINavigationBar.appearance().compactAppearance = appearance
        UINavigationBar.appearance().scrollEdgeAppearance = appearance
    } else {
        UINavigationBar.appearance().tintColor = .black
        UINavigationBar.appearance().barTintColor = myColor
        UINavigationBar.appearance().isTranslucent = false
    }

}

除了在应用程序打开时对 setBarColors() 的初始调用(工作正常)之外，我还像这样从应用程序内的 viewController 调用它，这对导航栏没有任何作用，甚至虽然该函数正在其参数中接收适当的数据:

    if detailFlag.issuedBy == "Canada"{
    appDelegate.setBarColors(issuingFlag: "Canada")

    }else if detailFlag.issuedBy == "US"{
    appDelegate.setBarColors(issuingFlag: "US")
    }

谁能帮我解释一下为什么函数不切换 navBar 颜色？

TIA!

Answer 1

我建议，因为您想根据 Flag 模型值动态更改 NavigationBar 主题(如背景颜色)，所以不要采用 AppDelegate 方式，因为它会为您做一次，并且被认为更多的是在实际创建任何 View 之前设置 NavigationBar 样式的全局方式。

有几种方法可以应用它，例如通过 extension ViewController、inheritance with base class.. 以及获取/设置标志的不同方法更改导航颜色的值，例如通过 userdefaults、variables...我将展示一个示例来帮助您继续:

import UIKit

class ViewController: BaseViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        currentFlag = "Canada"
    }
}

class BaseViewController: UIViewController {

    var currentFlag: String = "General" {
        didSet {
            setNavBarColor()
        }
    }

    private let themeColorUS = UIColor(red: 0.991, green: 0.621, blue: 0.022, alpha: 1.00)
    private let themeColorCanada = UIColor(red: 0.001, green: 0.686, blue: 0.000, alpha: 1.00)
    private let themeColorGeneral = UIColor(red: 0.000, green: 0.954, blue: 0.969, alpha: 1.00)

    override func viewDidLoad() {
        super.viewDidLoad()

        setNavBarColor()
    }

    private func setNavBarColor() {
        navigationController?.navigationBar.barTintColor = getBarColor(for: currentFlag)
    }

    private func getBarColor(for flag: String) -> UIColor {
        if flag == "US" {
            return themeColorUS
        } else if flag == "Canada" {
            return themeColorCanada
        }

        return themeColorGeneral
    }
}

这意味着，我们从 AppDelegate 中删除了设置其样式的全局方式，所以我的 didFinishLaunchingWithOptions 看起来像:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

    return true
}

运行以下代码(我的 ViewController 的标志设置为 Canada)，并在 Storyboard中使用 ViewController 和 UINavigationController 的 Root View Controller ，如下所示:

会让应用看起来像:

为改进而重构

你还可以做一些事情，只是为了更容易管理代码、标志和颜色，将它们组织在一个结构中，我选择了一个枚举作为例子，但你也可以用其他方式来做，只是给你一个例子，你可以这样做:

import UIKit

enum Flag {
    case us
    case canada
    case general

    static let `default` = Flag.general

    init(rawValue: String) {
        switch rawValue {
        case "US":
            self = .us
        case "Canada":
            self = .canada
        case "General":
            self = .general
        default:
            self = .default
        }
    }

    var themeColor: UIColor {
        switch self {
        case .us:
            return UIColor(red: 0.001, green: 0.686, blue: 0.000, alpha: 1.00)
        case .canada:
            return UIColor(red: 0.001, green: 0.686, blue: 0.000, alpha: 1.00)
        case .general:
            return UIColor(red: 0.000, green: 0.954, blue: 0.969, alpha: 1.00)
        }
    }
}

class ViewController: BaseViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        currentFlag = .canada
    }
}

class BaseViewController: UIViewController {

    var currentFlag: Flag = .default {
        didSet {
            setNavBarColor()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        setNavBarColor()
    }

    private func setNavBarColor() {
        navigationController?.navigationBar.barTintColor = currentFlag.themeColor
    }
}