Question

我试图在这里爬出众所周知的Neophyte深渊。

我开始掌握@EnvironmentObject的用法，直到在文档中注意到.environmentObject（）视图运算符为止。

这是我的代码：

import SwiftUI

struct SecondarySwiftUI: View {
    @EnvironmentObject var settings: Settings

    var body: some View {
        ZStack {
            Color.red
            Text("Chosen One: \(settings.pickerSelection.name)")
        }.environmentObject(settings) //...doesn't appear to be of use.
    }

    func doSomething() {}
}

我试图在视图上用.environmentObject（）运算符替换@EnvironmentObject的使用。
我因缺少“设置”定义而遇到了编译错误。

但是，该代码可以在没有.environmentObject运算符的情况下正常运行。

所以我的问题是，为什么要有.environmentObject运算符？

.environmentObject（）实例化一个environmentObject，而@environmentObject访问该实例化的对象吗？

Answer 1

以下是演示代码，用于显示EnvironmentObject和.environmentObject用法的变体（带有内联注释）：

struct RootView_Previews: PreviewProvider {
    static var previews: some View {
        RootView().environmentObject(Settings()) // environment object injection
    }
}

class Settings: ObservableObject {
    @Published var foo = "Foo"
}

struct RootView: View {
    @EnvironmentObject var settings: Settings // declaration for request of environment object

    @State private var showingSheet = false
    var body: some View {
        VStack {
            View1() // environment object injected implicitly as it is subview
            .sheet(isPresented: $showingSheet) {
                View2() // sheet is different view hierarchy, so explicit injection below is a must
                    .environmentObject(self.settings) // !! comment this out and see run-time exception
            }
            Divider()
            Button("Show View2") {
                self.showingSheet.toggle()
            }
        }
    }
}

struct View1: View {
    @EnvironmentObject var settings: Settings // declaration for request of environment object
    var body: some View {
        Text("View1: \(settings.foo)")
    }
}

struct View2: View {
    @EnvironmentObject var settings: Settings // declaration for request of environment object
    var body: some View {
        Text("View2: \(settings.foo)")
    }
}

因此，在您的代码中ZStack并不声明需要环境对象，因此不使用.environmentObject修饰符。

.environmentObject（）视图运算符与@EnvironmentObject的作用是什么？

1 个答案: