SwiftUI：不同视图之间的数据共享

问题描述

在视图之间共享变量的最佳做法是什么？ 我的应用程序只有一个视图。但随着它变得越来越复杂，我想我应该将它分成几个视图。还要分开方法。 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
}

我尝试了@Published、@Observedobject 和@Binding。但不要明白。提前感谢您的指点。

解决方法

有很多方法可以解决这个问题。

我的选择可能是将绑定传递给您需要访问的变量。这可能看起来像这样：

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 中，有一个参数传递给每个子视图，其中包含对 $ GlobalVars 属性的绑定（使用 str 符号）。

此外，doSomething 被移入了 ControlView

---

您也可以使用 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。它还允许子视图访问整个 ObservableObject，这并不是真正必要的。但是，它向您显示了主要内容：

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 通过使用 .environmentObject 放置在视图层次结构中传递给子项。每个子视图都可以通过声明 @EnvironmentObject var globalvars : GlobalVars

的属性来访问它

---

你也可以做一种混合模型，你显式地将 ObservableObject 作为参数传递给子视图：

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)
    }
}