在.onchange中添加视图修饰符

Question

是否可以在内部添加视图修饰符.onchange？

简化的示例：

content
  .onChange(of: publishedValue) {
    content.foregroundColor(.red)
  }

我有一个主题，当更改需要更改状态栏颜色时。我有一个为此创建的视图修饰符（ https://barstool.engineering/set-the--ios-status-bar-style-in-swiftui-in-swiftui-is-a-custom-view-modifier/ ）。修饰符正常工作，但是我需要将其更新为已发布的Value更改。

实际最小示例：

import SwiftUI

struct ContentView: View {
    @ObservedObject var viewModel: TestViewModel

    var body: some View {
        ZStack {
            Rectangle().foregroundColor(.mint)
            VStack(alignment: .center, spacing: 25) {
                Text("Test text \(viewModel.publishedValue)")
                    .onChange(of: viewModel.publishedValue) { newValue in
                        // Change status bar color
                        if viewModel.publishedValue % 2 == 0 {
                            self.body.statusBarStyle(.lightContent)
                        } else {
                            self.body.statusBarStyle(.darkContent)
                        }
                    }
                Button("Increment") {
                    viewModel.publishedValue += 1
                }
            }
        }
        .ignoresSafeArea()
        .statusBarStyle(.lightContent)
    }
}

class TestViewModel: ObservableObject {
    @Published var publishedValue: Int

    init(publishedValue: Int) {
        self.publishedValue = publishedValue
    }
}

extension View {
    /// Overrides the default status bar style with the given `UIStatusBarStyle`.
    ///
    /// - Parameters:
    ///   - style: The `UIStatusBarStyle` to be used.
    func statusBarStyle(_ style: UIStatusBarStyle) -> some View {
        return self.background(HostingWindowFinder(callback: { window in
            guard let rootViewController = window?.rootViewController else { return }
            let hostingController = HostingViewController(rootViewController: rootViewController, style: style)
            window?.rootViewController = hostingController
        }))
    }

}

fileprivate class HostingViewController: UIViewController {
    private var rootViewController: UIViewController?
    private var style: UIStatusBarStyle = .default

    init(rootViewController: UIViewController, style: UIStatusBarStyle) {
        self.rootViewController = rootViewController
        self.style = style
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        guard let child = rootViewController else { return }
        addChild(child)
        view.addSubview(child.view)
        child.didMove(toParent: self)
    }

    override var preferredStatusBarStyle: UIStatusBarStyle {
        return style
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        setNeedsStatusBarAppearanceUpdate()
    }
}

fileprivate struct HostingWindowFinder: UIViewRepresentable {
    var callback: (UIWindow?) -> ()

    func makeUIView(context: Context) -> UIView {
        let view = UIView()
        DispatchQueue.main.async { [weak view] in
            self.callback(view?.window)
        }
        return view
    }

    func updateUIView(_ uiView: UIView, context: Context) {
        // ...
    }
}

示例项目的github repo： https://github.com/iikeli/iikeli/iikeli/ikeli/view -Modifier-Test

Answer 1

简短的答案是否定的，但这并不意味着您不能使用它来根据某些.onchange（..）操作更改视图。例如。

@State var somethingChanged = false 
Text(somethingChanged ? "First Value" : "Second Value")

// Your code/view
    .onChange(..) {
         //Some Condition or whatever you want.
         somethingChanged = true
    }

您的用法可能看起来像这样。

content
    .foregroundColor(somethingChanged ? .red : .blue)
    .onChange(ofPublishedValue) {
        somethingChanged = true
    }

Answer 2

首先，感谢您的帮助。在我的情况下，这两个答案都没有帮助，因为我无法通过可变更改进行更新。但是，通过一些谷歌搜索并尝试了不同的解决方案，我发现了一种工作解决方案，以更新状态栏颜色。

我需要在hostingViewController中更新样式变量，然后相应地进行更新。因此，我将hostingViewController添加为@stateObject，并在.onchange（）中更新了样式变量。我要开始的解决方案并不是一开始，但确实有效。

代码：

import SwiftUI
import Introspect

struct ContentView: View {
    @ObservedObject var viewModel: TestViewModel
    @StateObject var hostingViewController: HostingViewController = .init(rootViewController: nil, style: .default)

    var body: some View {
        ZStack {
            Rectangle().foregroundColor(.mint)
            VStack(alignment: .center, spacing: 25) {
                Text("Test text \(viewModel.publishedValue)")
                    .onChange(of: viewModel.publishedValue) { newValue in
                        // Change status bar color
                        if viewModel.publishedValue % 2 == 0 {
                            hostingViewController.style = .lightContent
                        } else {
                            hostingViewController.style = .darkContent
                        }

                    }
                Button("Increment") {
                    viewModel.publishedValue += 1
                }
            }
        }
        .ignoresSafeArea()
        .introspectViewController { viewController in
            let window = viewController.view.window
            guard let rootViewController = window?.rootViewController else { return }
            hostingViewController.rootViewController = rootViewController
            window?.rootViewController = hostingViewController
        }
    }
}

class TestViewModel: ObservableObject {
    @Published var publishedValue: Int

    init(publishedValue: Int) {
        self.publishedValue = publishedValue
    }
}

class HostingViewController: UIViewController, ObservableObject {
    var rootViewController: UIViewController?

    var style: UIStatusBarStyle = .default {
        didSet {
            self.rootViewController?.setNeedsStatusBarAppearanceUpdate()
        }
    }

    init(rootViewController: UIViewController?, style: UIStatusBarStyle) {
        self.rootViewController = rootViewController
        self.style = style
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        guard let child = rootViewController else { return }
        addChild(child)
        view.addSubview(child.view)
        child.didMove(toParent: self)
    }

    override var preferredStatusBarStyle: UIStatusBarStyle {
        return style
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        setNeedsStatusBarAppearanceUpdate()
    }
}

这个答案给我所有实现解决方案所需的一切。注意：您可以覆盖rootviewController，但是您喜欢，我使用无论如何我们已经在项目中使用了它。

github branch

Answer 3

您正在解决这个问题。由于您的viewModel是@observedObject，而已发布Value IS 已发布，您的view> view 代码>每次更新都会自动重新计算。无需手动onChange。

您只需将逻辑移动到statusbarstyle的输入参数中即可。

var body: some View {
    ZStack {
        Rectangle().foregroundColor(.mint)
        VStack(alignment: .center, spacing: 25) {
            Text("Test text \(viewModel.publishedValue)")
            Button("Increment") {
                viewModel.publishedValue += 1
            }
        }
    }
    .ignoresSafeArea()
    .statusBarStyle(viewModel.publishedValue % 2 == 0 ? .lightContent : .darkContent)
}

甚至更好，将逻辑移至单独的计算属性：

var body: some View {
    ....
    .statusBarStyle(statusBarStyle)
}

private var statusBarStyle: UIStatusBarStyle {
    viewModel.publishedValue % 2 == 0 ? .lightContent : .darkContent
}