SwiftUI：自定义含Text的视图如何支持全部Text修饰符？

问题原因 #

在iOS 15里，.font是所有View都支持的环境类修饰符，会自动传递给子视图，所以能生效；但.tracking、.fontWeight这类是Text专属的实例方法，你的ScrollText是自定义View，本身没有这些方法，iOS 15不会自动把这些修饰符转发给内部的Text组件，所以只有.font能用。

解决方案 #

方案一：通过自定义环境变量传递修饰符（支持扩展更多修饰符）

这种方式通过环境变量把修饰符参数传递给内部Text，扩展性更强，后续要加其他Text修饰符也可以用类似逻辑：

1. 定义对应环境键，用来传递修饰符参数：

// 传递tracking参数的环境键
struct TrackingEnvironmentKey: EnvironmentKey {
    static let defaultValue: CGFloat? = nil
}

extension EnvironmentValues {
    var textTracking: CGFloat? {
        get { self[TrackingEnvironmentKey.self] }
        set { self[TrackingEnvironmentKey.self] = newValue }
    }
}

// 传递fontWeight参数的环境键
struct FontWeightEnvironmentKey: EnvironmentKey {
    static let defaultValue: Font.Weight? = nil
}

extension EnvironmentValues {
    var textFontWeight: Font.Weight? {
        get { self[FontWeightEnvironmentKey.self] }
        set { self[FontWeightEnvironmentKey.self] = newValue }
    }
}

2. 给View添加扩展，实现对应的修饰符方法，把参数存入环境变量：

extension View {
    func tracking(_ amount: CGFloat) -> some View {
        self.environment(\.textTracking, amount)
    }
    
    func fontWeight(_ weight: Font.Weight?) -> some View {
        self.environment(\.textFontWeight, weight)
    }
}

3. 修改ScrollText，读取环境变量并应用到内部的Text上：

struct ScrollText: View {
    let text: String
    @Environment(\.font) private var font
    @Environment(\.textTracking) private var tracking
    @Environment(\.textFontWeight) private var fontWeight
    
    var body: some View {
        Text("\(text) the logic is like that")
            .font(font)
            .applyIf(tracking != nil) { $0.tracking(tracking!) }
            .fontWeight(fontWeight)
    }
}

// 辅助工具：根据条件决定是否应用修饰符
extension View {
    func applyIf<Content: View>(_ condition: Bool, transform: (Self) -> Content) -> some View {
        condition ? transform(self) : self
    }
}

方案二：让ScrollText自身实现Text的修饰符方法（调用方式和原生Text完全一致）

直接在ScrollText里添加对应属性和修饰符方法，把参数传递给内部Text，调用起来和原生Text一模一样：

struct ScrollText: View {
    let text: String
    private var font: Font? = nil
    private var tracking: CGFloat? = nil
    private var fontWeight: Font.Weight? = nil
    
    var body: some View {
        Text("\(text) the logic is like that")
            .font(font)
            .applyIf(tracking != nil) { $0.tracking(tracking!) }
            .fontWeight(fontWeight)
    }
    
    // 实现font修饰符
    func font(_ font: Font?) -> ScrollText {
        var copy = self
        copy.font = font
        return copy
    }
    
    // 实现tracking修饰符
    func tracking(_ amount: CGFloat) -> ScrollText {
        var copy = self
        copy.tracking = amount
        return copy
    }
    
    // 实现fontWeight修饰符
    func fontWeight(_ weight: Font.Weight?) -> ScrollText {
        var copy = self
        copy.fontWeight = weight
        return copy
    }
}

// 辅助工具：根据条件决定是否应用修饰符
extension View {
    func applyIf<Content: View>(_ condition: Bool, transform: (Self) -> Content) -> some View {
        condition ? transform(self) : self
    }
}

两种方案都能让你在iOS 15里像使用原生Text一样，给ScrollText链式调用所有需要的修饰符。

内容的提问来源于stack exchange，提问作者Perry Wang