如何更新嵌入到 UIKit 中的 SwiftUI 视图? [英] How do I update a SwiftUI View that was embedded into UIKit?

问题描述

我正在为 UIKit 寻找等效于 AppKit 的 NSHostingView 以便我可以在 UIKit 中嵌入 SwiftUI 视图.不幸的是，UIKit 没有与 NSHostingView 等效的类.与 NSHostingController 等价的最接近的，名为 UIHostingController.由于视图控制器包含视图，我们应该能够调用适当的 UIViewController 嵌入方法，然后抓取查看并直接使用.

I'm looking for an equivalent of AppKit's NSHostingView for UIKit so that I can embed a SwiftUI view in UIKit. Unfortunately, UIKit does not have an equivalent class to NSHostingView. The closest we have as an equivalent of NSHostingController, named UIHostingController. Since a view controller contains a view, we should be able to call the appropriate UIViewController embedding methods, and then grab the view and use it directly.

那里 是 许多 文章 说明这是在 UIKit 中嵌入 SwiftUI 视图的方式.但是，他们通常无法解释您将如何从 UIKit ➡️ SwiftUI 进行通信.例如，假设我实现了一个用作进度条的 SwiftUI 视图，我希望定期更新进度.我希望我的旧版/UIKit 代码更新 SwiftUI 视图以显示新进度.

There are many articles that explain that this is the way to embed a SwiftUI view inside UIKit. However, they typically fall short in explaining how you would communicate from UIKit ➡️ SwiftUI. For example, imagine I implemented a SwiftUI view that acts as a progress bar, periodically, I'd like the progress to be updated. I want my legacy/UIKit code to update the SwiftUI view to display the new progress.

我发现的唯一一篇文章几乎解释了如何操作嵌入视图的内容，建议我们使用@ObservedObject:

The only article I found that came close to explaining how to manipulate an embedded view's content suggested we do so by using @ObservedObject:

import UIKit
import SwiftUI
import Combine

class CircleModel: ObservableObject {
    var didChange = PassthroughSubject<Void, Never>()

    var text: String { didSet { didChange.send() } }

    init(text: String) {
        self.text = text
    }
}

struct CircleView : View {
    @ObservedObject var model: CircleModel

    var body: some View {
        ZStack {
            Circle()
                .fill(Color.blue)
            Text(model.text)
                .foregroundColor(Color.white)
        }
    }
}

class ViewController: UIViewController {
    private weak var timer: Timer?
    private var model = CircleModel(text: "")

    override func viewDidLoad() {
        super.viewDidLoad()

        addCircleView()
        startTimer()
    }

    deinit {
        timer?.invalidate()
    }
}

private extension ViewController {
    func addCircleView() {
        let circleView = CircleView(model: model)
        let controller = UIHostingController(rootView: circleView)
        addChild(controller)
        controller.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(controller.view)
        controller.didMove(toParent: self)

        NSLayoutConstraint.activate([
            controller.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.5),
            controller.view.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.5),
            controller.view.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            controller.view.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
    }

    func startTimer() {
        var index = 0
        timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { [weak self] _ in
            index += 1
            self?.model.text = "Tick \(index)"
        }
    }
}

这似乎是有道理的，因为计时器应该触发更新视图的一系列事件:

This seems to make sense as the timer should trigger a chain of events that update the view:

1. ✅ self?.model.text = "Tick 1"(在 ViewController.startTimer() 中).
2. ✅ didChange.send()(在CircleModel.text.didSet中)
3. ❌ Text(model.text) (In CircleView.body)

1. ✅ self?.model.text = "Tick 1" (In ViewController.startTimer()).
2. ✅ didChange.send() (In CircleModel.text.didSet)
3. ❌ Text(model.text) (In CircleView.body)

正如您通过指标(指定是否运行某事)所见，问题在于 didChange.send() 永远不会触发 CircleView.body 的重新运行.

As you can see by the indicators (which specify if something was run or not), the problem is that didChange.send() never triggers a re-run of CircleView.body.

如何从 UIKit > SwiftUI 进行通信以操作嵌入在 UIKit 中的 SwiftUI 视图?

How do I communicate from UIKit > SwiftUI to manipulate a SwiftUI view that was embedded in UIKit?

推荐答案

你只需要扔掉那个自定义主题，使用标准的@Published，如下

All you need is to throw away that custom subject, and use standard @Published, as below

class CircleModel: ObservableObject {

    @Published var text: String

    init(text: String) {
        self.text = text
    }
}

测试:Xcode 11.2/iOS 13.2

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