SwiftUI:不同 View 之间的数据共享

Question

在 View 之间共享变量的最佳实践是什么？ 我的应用程序只有一个 View 。但随着它变得越来越复杂，我想我应该把它分成几个 View 。还要分离方法。 我从这样的事情开始:

struct ContentView: View {
    @State var str: String = "String"
    var body: some View {
        VStack(alignment: .leading) {
            Text(str)
            TextField("Input", text: $str)
            Button("button", action: { doSomething() })
        }.padding()
    }
    func doSomething() {
        str = str + " " + str
    }
}

想去那里:

class GlobalVars: ObservableObject {
    @Published var str: String = "Initial String"
}
struct ContentView: View {
    @ObservedObject var globalvars = GlobalVars()
    var body: some View {
        VStack(alignment: .leading) {
            DisplayView()
            EditView()
            ControlView()
        }.padding()
    }
}
struct DisplayView: View {
    @Binding var str:  String
    var body: some View {
        Text(self.globalvars.str)
    }
}
struct EditView: View {
    @Binding var str:  String
    var body: some View {
        TextField("Input", text: self.$str)
    }
}
struct ControlView: View {
    @Binding var str:  String
    var body: some View {
        Button("button", action: { doSomething() })
    }
}
func doSomething() {
    @Binding var str:  String
    self.str = self.str + " " + self.str
}

我尝试使用@Published、@ObservedObject 和@Binding。但别明白。感谢您提前提供任何指示。

Answer 1

有多种方法可以解决这个问题。

我的选择可能是将绑定(bind)传递给您需要访问的变量。可能看起来像这样:

class GlobalVars: ObservableObject {
    @Published var str: String = "Initial String"
}
struct ContentView: View {
    @ObservedObject var globalvars = GlobalVars()
    var body: some View {
        VStack(alignment: .leading) {
            DisplayView(str: globalvars.str) //don't need a binding here since it doesn't get modified
            EditView(str: $globalvars.str)
            ControlView(str: $globalvars.str)
        }.padding()
    }
}
struct DisplayView: View {
    var str:  String //don't need a binding here since it doesn't get modified
    var body: some View {
        Text(str)
    }
}
struct EditView: View {
    @Binding var str:  String
    var body: some View {
        TextField("Input", text: $str)
    }
}
struct ControlView: View {
    @Binding var str:  String
    var body: some View {
        Button("button", action: { doSomething() })
    }
    
    func doSomething() {
        str = str + " " + str
    }
}

请注意，现在在 ContentView ，有一个参数传递给每个 subview ，其中包含到 $ 的绑定(bind)(使用 GlobalVars 符号) str属性。

此外，doSomething被移入ControlView的 body

---

您还可以使用EnvironmentObject 来处理此问题。我个人不太喜欢这种方法，因为我宁愿明确地看到我的参数的去向。它还允许 subview 访问整个 ObservableObject，但这并不是真正必要的。但是，它向您展示了原理:

class GlobalVars: ObservableObject {
    @Published var str: String = "Initial String"
}
struct ContentView: View {
    @ObservedObject var globalvars = GlobalVars()
    var body: some View {
        VStack(alignment: .leading) {
            DisplayView()
            EditView()
            ControlView()
        }.padding()
        .environmentObject(globalvars)
    }
}
struct DisplayView: View {
    @EnvironmentObject var globalvars : GlobalVars
    var body: some View {
        Text(globalvars.str)
    }
}
struct EditView: View {
    @EnvironmentObject var globalvars : GlobalVars
    var body: some View {
        TextField("Input", text: $globalvars.str)
    }
}
struct ControlView: View {
    @EnvironmentObject var globalvars : GlobalVars
    var body: some View {
        Button("button", action: { doSomething() })
    }
    
    func doSomething() {
        globalvars.str = globalvars.str + " " + globalvars.str
    }
}

请注意，现在，globalvars通过将 .environmentObject 放置在 View 层次结构中来传递给子级。每个 subview 都可以通过声明 @EnvironmentObject var globalvars : GlobalVars 属性来访问它。

---

您还可以采用一种混合模型，将 ObservableObject 作为参数显式传递给 subview :

struct ContentView: View {
    @ObservedObject var globalvars = GlobalVars()
    var body: some View {
        VStack(alignment: .leading) {
            DisplayView(globalvars: globalvars)
        }.padding()
        .environmentObject(globalvars)
    }
}

struct DisplayView: View {
    @ObservedObject var globalvars : GlobalVars
    var body: some View {
        Text(globalvars.str)
    }
}