带有选项的SwiftUI选择器在iOS16中没有选择

Question

我使用Picker选项进行无选择，在iOS15中它工作得很好，但是在iOS16中它有一个默认值，如何删除这个默认值，当选择为零时，我不需要将文本显示在Picker行的右边。

struct ContentView: View {
    
    @State private var selection: String?
    let strengths = ["Mild", "Medium", "Mature"]
    
    var body: some View {
        NavigationView {
            List {
                Section {
                    Picker("Strength", selection: $selection) {
                        ForEach(strengths, id: \.self) {
                            Text($0).tag(Optional($0))
                        }
                    }
                }
            }
        }
    }
}

在iOS15中，当选择为零时，不会在选择器行的右侧显示文本。

​

但是在iOS 16中，相同的代码导致不同的结果，当选择为零时，它有一个默认值。

​

Answer 1

Xcode 14.1 Beta 3日志："Picker:选择“"nil”无效，并且没有关联的标记，这将提供未定义的结果。

要解决这个日志，您需要添加一个使用nil标记的选项。

struct ContentView: View {

    @State private var selection: String?
    let strengths = ["Mild", "Medium", "Mature"]

    var body: some View {
        NavigationView {
            List {
                Section {
                    Picker("Strength", selection: $selection) {
                        Text("No Option").tag(Optional<String>(nil))
                        ForEach(strengths, id: \.self) {
                            Text($0).tag(Optional($0))
                        }
                    }
                    Text("current selection: \(selection ?? "none")")
                }
            }
        }
    }
}

Answer 2

这就是我在iOS 14.0.1中为XCode 16.0所做的事情(为了避免用户对iOS 16.0设备感到烦躁)：

let promptText: String = "select" // just a default String
    
//short one for your example
Section {
    Picker("Strength", selection: $selection) {
        if selection == nil { // this will work, since there is no initialization to the optional value in your example
            Text(promptText).tag(Optional<String>(nil)) // is only shown until a selection is made
        }
        ForEach(strengths, id: \.self) {
            Text($0).tag(Optional($0))
        }
    }
}
    
// more universal example
Section {
    Picker("Strength", selection: $selection) {
        if let safeSelection = selection{
            if !strengths.contains(safeSelection){ // does not care about a initialization value as long as it is not part of the collection 'strengths'
                Text(promptText).tag(Optional<String>(nil)) // is only shown until a selection is made
            }
        }else{
            Text(promptText).tag(Optional<String>(nil))
        }
        ForEach(strengths, id: \.self) {
            Text($0).tag(Optional($0))
        }
    }
}
    
// Don't want to see anything if nothing is selected? empty String "" leads to an warning. Go with non visual character like " " or 'Horizontal Tab'. But then you will get an empty row...
Section {
    let charHorizontalTab: String = String(Character(UnicodeScalar(9)))
    Picker("Strength", selection: $selection) {
        if let safeSelection = selection{
            if !strengths.contains(safeSelection){ // does not care about a initialization value as long as it is not part of the collection 'strengths'
                Text(charHorizontalTab).tag(Optional<String>(nil)) // is only shown until a selection is made
            }
        }else{
            Text(charHorizontalTab).tag(Optional<String>(nil))
        }
        ForEach(strengths, id: \.self) {
            Text($0).tag(Optional($0))
        }
    }
}

祝你好运，找到适合你的解决方案。