不使用垫片定位视图底部

问题描述

如何在不使用间隔器的情况下将视图定位在底部.我知道我可以实现它在 VStack 中放置一个垫片和我的视图，但我不想使用垫片，因为我不希望我的视图占据所有垂直空间.使用 UIKit，我会将其放置在安全区域底部指南中.

How can I position a View at the bottom without using a spacer. I know I can achieve it placing a spacer and my view in inside a VStack but I don't want to use a spacer because I don't want my view to take up all the vertical space. With UIKit I would position it at safe area bottom guide.

推荐答案

尝试不同的方法我最终创建了自己的自定义容器，它有一些已知的限制，完全满足我的需求.希望对其他人有所帮助.

Experimenting with different approaches I finally end up with creating own custom container, which, having some known limitation, fulfils my needs completely. Hope it would be helpful for someone else.

演示:

优点:ContentView &PinnedView在布局上绝对独立，自动处理设备方向，内部内容实际上是无限的

Pros: ContentView & PinnedView are absolutely independent in layout on each other, automatically handle device orientation, and actually limitless in internal content

缺点:由于使用 GeometryReader 在顶级内容或固定视图中使用 .infinity 导致鸡-蛋"问题导致崩溃.

Cons: Due to used GeometryReader using .infinity at top-level content or pinned view result in crash due to "chicken-egg" problem.

容器代码:

struct ContainerWithPinnedBottomView<Content, Pinned>: View
                                     where Content: View, Pinned: View {

    private var content: () -> Content
    private var bottomView: () -> Pinned

    @inlinable public init(@ViewBuilder pinnedView: @escaping () -> Pinned,
                            @ViewBuilder content: @escaping () -> Content) {
        self.content = content
        self.bottomView = pinnedView
    }

    var body: some View {
        ZStack(alignment: .bottom) {
            Rectangle().fill(Color.clear) // !! Extends ZStack to full screen
            GeometryReader { _ in
                ZStack {
                    self.content()
                }
            }
            self.bottomView()
                .alignmentGuide(.bottom) { $0[.bottom] }
        }
    }

}

使用示例(演示截图)

struct TestBottomView: View {
    var body: some View {
        ContainerWithPinnedBottomView(pinnedView: {
            HStack {
                Spacer()
                Text("Always Pinned to Bottom")
                    .padding()
    //                .frame(width: .infinity) // !! LIMITATION - don't use, cycling crash
                Spacer()
            }
            .background(Color.blue)
        }) {
            NavigationView {
                List (0 ..< 100, id: .self) { i in
                    NavigationLink(destination: Text("Other")) {
                        Text("Row (i)")
                    }
                }
                .navigationBarTitle("TitleBar")
            }
        }
    }
}

struct TestBottomView_Previews: PreviewProvider {
    static var previews: some View {
        TestBottomView()
    }
}

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