SwiftUI中无需DatePickerStyle修改DatePicker字体与字重的方法

不存在无需借助DatePickerStyle的直接方法来修改SwiftUI DatePicker的字体和字重。默认情况下，SwiftUI的DatePicker（尤其是紧凑样式）的内部文本元素是系统封装的，.font()修饰符只能作用于DatePicker的外部容器，无法穿透到内部的日期显示文本上，这就是你代码里该修饰符无效的原因。

下面提供两种可行的解决思路：

1. 自定义DatePickerStyle #

通过实现自定义DatePickerStyle，可以完全控制DatePicker的显示内容，包括字体设置：

struct CustomDatePickerStyle: DatePickerStyle {
    func makeBody(configuration: Configuration) -> some View {
        Button(action: {
            configuration.presentationMode.wrappedValue.toggle()
        }) {
            Text(configuration.date.formatted(date: .abbreviated, time: .omitted))
                .font(.custom("HelveticaNeue-Thin", size: 10, relativeTo: .caption))
                .foregroundColor(.primary)
        }
        .popover(isPresented: configuration.presentationMode) {
            DatePicker("", selection: configuration.$selection, displayedComponents: .date)
                .datePickerStyle(.graphical)
                .padding()
        }
    }
}

// 使用方式
DatePicker("Start date",
           selection: Binding(get:{goal.startDate!},set:{goal.startDate = $0}),
           displayedComponents: .date
)
.datePickerStyle(CustomDatePickerStyle())
.labelsHidden()

2. 用UIViewRepresentable包装UIDatePicker #

借助UIKit的UIDatePicker可以直接设置字体，再包装成SwiftUI组件使用：

struct UIKitDatePicker: UIViewRepresentable {
    @Binding var date: Date
    let displayedComponents: UIDatePicker.Component

    func makeUIView(context: Context) -> UIDatePicker {
        let picker = UIDatePicker()
        picker.datePickerMode = .date
        picker.addTarget(context.coordinator, action: #selector(Coordinator.dateChanged), for: .valueChanged)
        // 直接设置字体
        picker.font = UIFont(name: "HelveticaNeue-Thin", size: UIFont.captionSize)
        picker.preferredDatePickerStyle = .compact
        return picker
    }

    func updateUIView(_ uiView: UIDatePicker, context: Context) {
        uiView.date = date
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    class Coordinator: NSObject {
        let parent: UIKitDatePicker

        init(_ parent: UIKitDatePicker) {
            self.parent = parent
        }

        @objc func dateChanged(_ sender: UIDatePicker) {
            parent.date = sender.date
        }
    }
}

// 使用方式
UIKitDatePicker(date: Binding(get:{goal.startDate!},set:{goal.startDate = $0}), displayedComponents: .date)

内容的提问来源于stack exchange，提问作者quaternionboy