使用条件运算符搭配.labelStyle修饰符出现报错问题

需求：当isTextVisible为false时，Label显示标题和图标；当isTextVisible为true时，仅显示图标。但使用三元运算符给.labelStyle赋值时，出现编译错误："Trailing closure passed to parameter of type 'FormStyleConfiguration' that does not accept a closure"

原代码如下：

import SwiftUI

struct ContentView: View {

    @State private var text = ""
    @State private var isTextVisible: Bool = false

    var body: some View {

        HStack {
            Button {
                withAnimation {
                    isTextVisible.toggle()
                    text = ""
                }
            } label: {
                Label(isTextVisible ? "Delete" : "Add", systemImage: isTextVisible ? "minus.circle.fill" : "plus.circle.fill")
                    .labelStyle(isTextVisible ? .iconOnly : .titleAndIcon) // 触发错误的行
                    .symbolRenderingMode(.palette)
                    .foregroundStyle(.white, isTextVisible ? .red : .green)
            }
            if isTextVisible {
                TextField("", text: $text)
            }
        }
    }
}

问题根源：LabelStyle的.iconOnly和.titleAndIcon是不同的具体类型，Swift无法通过三元运算符推断出统一的LabelStyle类型，导致类型不匹配错误。

方法一：条件分支创建Label #

通过@ViewBuilder分别创建两种状态下的Label，各自应用对应的LabelStyle：

import SwiftUI

struct ContentView: View {

    @State private var text = ""
    @State private var isTextVisible: Bool = false

    var body: some View {

        HStack {
            Button {
                withAnimation {
                    isTextVisible.toggle()
                    text = ""
                }
            } label: {
                @ViewBuilder
                var dynamicLabel: some View {
                    if isTextVisible {
                        Label("Delete", systemImage: "minus.circle.fill")
                            .labelStyle(.iconOnly)
                    } else {
                        Label("Add", systemImage: "plus.circle.fill")
                            .labelStyle(.titleAndIcon)
                    }
                }
                dynamicLabel
                    .symbolRenderingMode(.palette)
                    .foregroundStyle(.white, isTextVisible ? .red : .green)
            }
            if isTextVisible {
                TextField("", text: $text)
            }
        }
    }
}

方法二：自定义动态LabelStyle #

创建一个自定义的DynamicLabelStyle，通过传入的布尔值控制显示方式：

import SwiftUI

struct DynamicLabelStyle: LabelStyle {
    let showText: Bool
    
    func makeBody(configuration: Configuration) -> some View {
        if showText {
            Label(configuration.title, icon: configuration.icon)
                .labelStyle(.titleAndIcon)
        } else {
            Label(configuration.title, icon: configuration.icon)
                .labelStyle(.iconOnly)
        }
    }
}

// 扩展LabelStyle方便调用
extension LabelStyle where Self == DynamicLabelStyle {
    static func dynamic(showText: Bool) -> DynamicLabelStyle {
        DynamicLabelStyle(showText: showText)
    }
}

struct ContentView: View {

    @State private var text = ""
    @State private var isTextVisible: Bool = false

    var body: some View {

        HStack {
            Button {
                withAnimation {
                    isTextVisible.toggle()
                    text = ""
                }
            } label: {
                Label(isTextVisible ? "Delete" : "Add", systemImage: isTextVisible ? "minus.circle.fill" : "plus.circle.fill")
                    .labelStyle(.dynamic(showText: !isTextVisible)) // isTextVisible为false时显示文本
                    .symbolRenderingMode(.palette)
                    .foregroundStyle(.white, isTextVisible ? .red : .green)
            }
            if isTextVisible {
                TextField("", text: $text)
            }
        }
    }
}

内容的提问来源于stack exchange，提问作者0x1801ce