swiftui简单的实现选项卡效果,同时初次加载

pageView code

struct PageView<SelectionValue, Content>: View where SelectionValue: Hashable, Content: View {
    @Binding private var selection: SelectionValue
    private let indexDisplayMode: PageTabViewStyle.IndexDisplayMode
    private let indexBackgroundDisplayMode: PageIndexViewStyle.BackgroundDisplayMode
    private let content: () -> Content

    init(
        selection: Binding<SelectionValue>,
        indexDisplayMode: PageTabViewStyle.IndexDisplayMode = .automatic,
        indexBackgroundDisplayMode: PageIndexViewStyle.BackgroundDisplayMode = .automatic,
        @ViewBuilder content: @escaping () -> Content
    ) {
        self._selection = selection
        self.indexDisplayMode = indexDisplayMode
        self.indexBackgroundDisplayMode = indexBackgroundDisplayMode
        self.content = content
        print(selection)
        print(indexDisplayMode)
        print(indexBackgroundDisplayMode)
    }

    var body: some View {
        TabView(selection: $selection) {
            content()
        }
        .tabViewStyle(PageTabViewStyle(indexDisplayMode: indexDisplayMode))
        .indexViewStyle(PageIndexViewStyle(backgroundDisplayMode: indexBackgroundDisplayMode))
    }
}

extension PageView where SelectionValue == Int {
    init(
        indexDisplayMode: PageTabViewStyle.IndexDisplayMode = .automatic,
        indexBackgroundDisplayMode: PageIndexViewStyle.BackgroundDisplayMode = .automatic,
        @ViewBuilder content: @escaping () -> Content
    ) {
        self._selection = .constant(0)
        self.indexDisplayMode = indexDisplayMode
        self.indexBackgroundDisplayMode = indexBackgroundDisplayMode
        self.content = content
    }
}

struct TestPageView1:View {
    var body: some View{
        Text("1")
            .onLoad {
                print("初次加载1")
            }
    }
}
struct TestPageView2:View {
    var body: some View{
        Text("2")
            .onLoad {
                print("初次加载2")
            }
    }
}
struct TestPageView3:View {
    var body: some View{
        Text("3")
            .onLoad {
                print("初次加载3")
            }
    }
}

struct Test_PageView:View {
    @State var selection = 1
    var body: some View {
        VStack {
            Text("Selection: \(selection)")
            PageView(selection: $selection, indexBackgroundDisplayMode: .never) {
                TestPageView1()
                TestPageView2()
                TestPageView3()
            }
        }
    }
}

onLoad code

struct ViewDidLoadModifier: ViewModifier {

    @State private var didLoad = false
    private let action: (() -> Void)?

    init(perform action: (() -> Void)? = nil) {
        self.action = action
    }

    func body(content: Content) -> some View {
        content.onAppear {
            if didLoad == false {
                didLoad = true
                action?()
            }
        }
    }

}

extension View {

    func onLoad(perform action: (() -> Void)? = nil) -> some View {
        modifier(ViewDidLoadModifier(perform: action))
    }

}