ios - 如何创建一个带有可选辅助 View 参数的 SwiftUI View ？

Question

我正在尝试创建一个自定义 SwiftUI View ，它的行为类似于默认 View ，我可以在其中使用方法或可选的初始化参数向 View 添加额外内容。

SomeCustomView(title: "string argument") {
    // some view
}

SomeCustomView(title: "hello") {
    // some view
}.sideContent {
    // another view
}

// This style is acceptable too
SomeCustomView(title: "hello", sideContent: { /* another view */ }) {
    // some view
}

我如何修改这个 View 结构使其表现得像上面的例子一样？

struct SomeCustomView<Content>: View where Content: View {
    let title: String
    let content: Content

    init(title: String, @ViewBuilder content: () -> Content) {
        self.title = title
        self.content = content()
    }

    var body: some View {
        VStack {
            Text(title)
            content
        }
    }
}

理想情况下，我有两个不同的主体"template"，我可以根据是否调用了 sideContent 方法或设置了 sideContent 参数在它们之间切换。例如，

var body: some View {
    VStack {
        Text(title)
        content
    }
}

// or

var otherBody: some View {
    HStack {
        VStack {
            Text(title)
            content
        }
        sideContent
    }
}

Answer 1

2021 年 11 月更新(适用于 Xcode 11.x、12.x 和 13.x)

经过一番思考和反复试验，我想通了。事后看来，这似乎有点明显。

struct SomeCustomView<Content>: View where Content: View {
    let title: String
    let content: Content

    init(title: String, @ViewBuilder content: @escaping () -> Content) {
        self.title = title
        self.content = content()
    }

    // returns a new View that includes the View defined in 'body'
    func sideContent<SideContent: View>(@ViewBuilder side: @escaping () -> SideContent) -> some View {
        HStack {
            self     // self is SomeCustomView
            side() 
        }
    }

    var body: some View {
        VStack {
            Text(title)
            content
        }
    }
}

无论有没有方法调用，它都可以工作。

SomeCustomView(title: "string argument") {
    // some view
}

SomeCustomView(title: "hello") {
    // some view
}.sideContent {
    // another view
}

以前的代码有细微的错误:body 应该是 self

    func sideContent<SideContent: View>(@ViewBuilder side: @escaping () -> SideContent) -> some View {
        HStack {
            body // <--- subtle bug, updates to the main View are not propagated 
            side() 
        }
    }

感谢 Jordan Smith 很久以前就指出了这一点。