如何在 SwiftUI 的列表中设置和使用参数“选择”

Question

我已经了解了 SwiftUI，但在理解 SwiftUI 中的 List 时遇到困难。

列表定义如下。

@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
public struct List<SelectionValue, Content> : View where SelectionValue : Hashable, Content : View {

    /// Creates a List that supports multiple selection.
    ///
    /// - Parameter selection: A binding to a set that identifies the selected
    ///   rows.
    ///
    /// - See Also: `View.selectionValue` which gives an identifier to the rows.
    ///
    /// - Note: On iOS and tvOS, you must explicitly put the `List` into Edit
    ///   Mode for the selection to apply.
    @available(watchOS, unavailable)
    public init(selection: Binding<Set<SelectionValue>>?, @ViewBuilder content: () -> Content)

    /// Creates a List that supports optional single selection.
    ///
    /// - Parameter selection: A binding to the optionally selected row.
    ///
    /// - See Also: `View.selectionValue` which gives an identifier to the rows.
    ///
    /// - Note: On iOS and tvOS, you must explicitly put the `List` into Edit
    ///   Mode for the selection to apply.
    @available(watchOS, unavailable)
    public init(selection: Binding<SelectionValue?>?, @ViewBuilder content: () -> Content)

    :
    :

}

那么我的问题是，如何才能拥有支持多选/单选的List？我会知道如何设置Binding<Set<SelectionValue>>?和的参数Binding<Set<SelectionValue>>?。

我已经阅读了如何在 SwiftUI 列表中启用选择，并且我已经得到了这段代码。该代码确实支持多项选择。

var demoData = ["Phil Swanson", "Karen Gibbons", "Grant Kilman", "Wanda Green"]

struct ContentView: View {
    @State var selectKeeper = Set<String>()

    var body: some View {
        NavigationView {
            List(demoData, id: \.self, selection: $selectKeeper){ name in
                Text(name)
            }
            .navigationBarItems(trailing: EditButton())
            .navigationBarTitle(Text("Selection Demo \(selectKeeper.count)"))
        }
    }
}

但仍然无法理解如何设置参数“选择”并设置类型。如何更改为单选列表？什么是Set<String>()...？

有谁解释得通俗易懂吗？我会有一个简单的例子...

非常感谢您，老师！感谢您阅读我的问题！！

Answer 1

如何更改为单选列表？

@State var selectKeeper: String? = nil // << default, no selection

什么是 Set()...？

所选项目的容器，在您的情况下为字符串demoData

我如何设置参数“选择”并设置类型

一种变体.onAppear如下

List(demoData, id: \.self, selection: $selectKeeper){ name in
    Text(name)
}
.onAppear {
   self.selectKeeper = [demoData[0]]
}

选择的类型是通过状态变量的类型来检测的，如果设置为多选，则为单选。