SwiftUI:如何遍历可绑定对象的数组? [英] SwiftUI: How to iterate over an array of bindable objects?

问题描述

我正在尝试学习SwiftUI，以及绑定如何工作.

I'm trying to learn SwiftUI, and how bindings work.

我有可以运行的代码，其中显示了项目列表.点击一个项目后，对该项目的绑定将传递给子视图:

I have this code that works, that shows a list of projects. When one project is tapped, a binding to that project is passed to the child view:

struct ProjectsView: View {
  @ObjectBinding var state: AppState
  @State var projectName: String = ""

  var body: some View {
    NavigationView {
      List {
        ForEach(0..<state.projects.count) { index in
          NavigationLink(destination: ProjectView(project: self.$state.projects[index])) {
            Text(self.state.projects[index].title)
          }
        }
      }
      .navigationBarTitle("Projects")
    }
  }
}

子视图，我在其中使用绑定对项目进行变异:

The child view, where I'm mutating the project using a binding:

struct ProjectView: View {
  @Binding var project: Project
  @State var projectName: String = ""

  var body: some View {
    VStack {
      Text(project.title)
      TextField(
        $projectName,
        placeholder: Text("Change project name"),
        onCommit: {
          self.project.title = self.projectName
          self.projectName = ""
      })
      .padding()
    }
  }
}

但是，我宁愿在不使用索引的情况下遍历project数组(因为我想学习，并且更易于阅读)，但是不确定如何将绑定传递给单个项目.我这样尝试过，但是后来我无法访问project.title，因为它是绑定，而不是字符串.

However, I would rather iterate over the projects array without using indexes (beacuse I want to learn, and its easier to read), but not sure how I then can pass the binding to a single project. I tried it like this, but then I can't get access to project.title, since it's a binding, and not a String.

ForEach($state.projects) { project in
  NavigationLink(destination: ProjectView(project: project)) {
    Text(project.title)
  }
}

我该如何实现?

推荐答案

注意:我使用Xcode 11.2，@ ObjectBinding已被废弃(因此您需要更新以验证以下代码).

Note: I use Xcode 11.2, @ObjectBinding is obsoleted in it (so you need to update to verify below code).

我询问了模型，因为它对于方法可能很重要.对于类似的功能，我更喜欢Combine的ObservableObject，因此模型不是值类型的引用.

I asked about model, because it might matter for approach. For similar functionality I preferred Combine's ObservableObject, so model is reference not value types.

这是我针对您的情况进行调整的方法.它不完全符合您的要求，因为ForEach需要一些序列，但是您尝试使用不受支持的类型来填充它.

Here is the approach, which I tune for your scenario. It is not exactly as you requested, because ForEach requires some sequence, but you try to feed it with unsupported type.

无论如何，您可能会在下面将其视为替代项(它是无索引的).它是完整的模块，因此您可以将其粘贴到Xcode 11.2中并在预览中进行测试.希望这会有所帮助.

Anyway you may consider below just as alternate (and it is w/o indexes). It is complete module so you can paste it in Xcode 11.2 and test in preview. Hope it would be helpful somehow.

预览:

解决方案:

import SwiftUI
import Combine

class Project: ObservableObject, Identifiable {
    var id: String = UUID().uuidString
    @Published var title: String = ""

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

class AppState: ObservableObject {
    @Published var projects: [Project] = []
    init(_ projects: [Project]) {
        self.projects = projects
    }
}

struct ProjectView: View {
  @ObservedObject var project: Project
  @State var projectName: String = ""

  var body: some View {
    VStack {
      Text(project.title)
      TextField("Change project name",
        text: $projectName,
        onCommit: {
          self.project.title = self.projectName
          self.projectName = ""
      })
      .padding()
    }
  }
}

struct ContentView: View {
    @ObservedObject var state: AppState = AppState([Project(title: "1"), Project(title: "2")])
    @State private var refreshed = false

    var body: some View {
        NavigationView {
            List {
                ForEach(state.projects) { project in
                  NavigationLink(destination: ProjectView(project: project)) {
                    // !!!  existance of .refreshed state property somewhere in ViewBuilder
                    //      is important to inavidate view, so below is just a demo
                    Text("Named: \(self.refreshed ? project.title : project.title)")
                  }
                  .onReceive(project.$title) { _ in
                        self.refreshed.toggle()
                    }
                }
            }
            .navigationBarTitle("Projects")
            .navigationBarItems(trailing: Button(action: {
                self.state.projects.append(Project(title: "Unknown"))
            }) {
                Text("New")
            })
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

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