SwiftUI中修改Binding属性导致页面自动返回的问题求助

将PctView推入NavigationView导航栈后，在PctView中修改Binding绑定的completionPct数值时，页面会自动关闭返回，相关代码如下：

import SwiftUI
struct Technology: Identifiable {
  var id: UUID = UUID()
  var techName: String
  var completionPct: Float = 0.0
}
struct parentView: View {
  @State var technology = Technology(techName: "Front End")
  @State var tempList = [1,2]
  var body: some View {
    NavigationView {
      VStack {
        NavigationLink {
          ChildView(technology: $technology)
        } label: {
          Text(technology.techName)
        }
      }.navigationTitle(technology.techName)
    }
  }
}
struct ChildView: View {
  @Binding var technology: Technology
  var body: some View {
    VStack {
      Text(technology.techName)
      NavigationLink {
        PctView(completionPct: $technology.completionPct)
      } label: {
        Text("Go To Pct Changing View")
      }.navigationTitle(technology.techName)
    }
  }
}
struct PctView: View {
  @Binding var completionPct: Float
  var body: some View {
    Button("Change Pct") {
      completionPct = completionPct + 0.1
    }.navigationTitle("Pct View")
  }
}
struct Test: PreviewProvider {
  static var previews: some View {
    parentView()
  }
}

原因分析 #

核心问题在于Technology是值类型（结构体）。值类型的特性是：修改其内部属性时，会生成一个全新的实例替换原实例。而parentView中的NavigationLink直接依赖这个technology实例，当实例被替换后，SwiftUI会判定导航链路的数据源发生了根本性变化，从而重新渲染整个导航结构，导致当前的PctView被弹出，自动返回上一级页面。

解决思路 #

方案1：将结构体改为引用类型（类） #

把Technology从结构体改成类，这样修改内部属性时不会生成新实例，只是修改现有实例的属性，SwiftUI不会触发导航链路的重建。

修改后的代码：

import SwiftUI

class Technology: Identifiable {
  var id: UUID = UUID()
  var techName: String
  var completionPct: Float = 0.0
  
  init(techName: String) {
    self.techName = techName
  }
}

struct parentView: View {
  @StateObject var technology = Technology(techName: "Front End")
  @State var tempList = [1,2]
  
  var body: some View {
    NavigationView {
      VStack {
        NavigationLink {
          ChildView(technology: technology)
        } label: {
          Text(technology.techName)
        }
      }.navigationTitle(technology.techName)
    }
  }
}

struct ChildView: View {
  @ObservedObject var technology: Technology
  
  var body: some View {
    VStack {
      Text(technology.techName)
      NavigationLink {
        PctView(completionPct: $technology.completionPct)
      } label: {
        Text("Go To Pct Changing View")
      }.navigationTitle(technology.techName)
    }
  }
}

struct PctView: View {
  @Binding var completionPct: Float
  
  var body: some View {
    Button("Change Pct") {
      completionPct = completionPct + 0.1
    }.navigationTitle("Pct View")
  }
}

struct Test: PreviewProvider {
  static var previews: some View {
    parentView()
  }
}

修改要点：

• 将Technology改为类并添加初始化方法
• parentView用@StateObject管理类实例，确保生命周期正确
• ChildView用@ObservedObject接收类实例，监听属性变化

方案2：单独抽离绑定属性（保留结构体） #

如果坚持使用结构体，可以把completionPct单独作为@State变量抽离出来，避免修改整个结构体实例，示例如下：

struct parentView: View {
  @State var techName = "Front End"
  @State var completionPct: Float = 0.0
  @State var tempList = [1,2]
  
  var body: some View {
    NavigationView {
      VStack {
        NavigationLink {
          ChildView(techName: techName, completionPct: $completionPct)
        } label: {
          Text(techName)
        }
      }.navigationTitle(techName)
    }
  }
}

struct ChildView: View {
  let techName: String
  @Binding var completionPct: Float
  
  var body: some View {
    VStack {
      Text(techName)
      NavigationLink {
        PctView(completionPct: $completionPct)
      } label: {
        Text("Go To Pct Changing View")
      }.navigationTitle(techName)
    }
  }
}

这样修改completionPct时，只会更新单个变量，不会触发整个结构体的替换，导航页面也就不会自动返回了。

内容的提问来源于stack exchange，提问作者Aaban Tariq Murtaza