在macOS上用Swift获取字体样式及解决视图渲染与更新问题

我正在制作一个展示特定字体样式的菜单，目前遇到两个核心问题：

• 注释的ForEach代码无法正常渲染列表：当前按钮代码能正确打印字体样式，但没法通过ForEach遍历渲染样式选项。getFontStyles()返回数组的数组，内部数组包含字体名称、样式、ID编号等字段，可通过member[1]获取样式内容。
• .onChange完全不触发：补充代码和参考代码结构相近，仅变量名不同，我添加了多个.onChange调用，试图在切换字体时更新字体样式列表，但所有.onChange均未生效。

初始代码 #

struct AddFontStyleItems: View {
    var dm: DrawModel
    init(_ dm: DrawModel ) { self.dm = dm }
    
    var body: some View {
    var fontStyles = getFontStyles(for: dm.curFont )
//      ForEach(fontStyles, id: \.self) { curStyle in
//          Button( "xxx" ) {
//              print( "Style: \(curStyle)")
//      //      print("Type of Member: \(type(of: member)) - \(member[1])")
//          }
//      }
        Button( "xxx" ) {
            let fontStyles = NSFontManager.shared.availableMembers(ofFontFamily: dm.curFont)
            print("-\nFont: \(dm.curFont)")
            
            if let members = fontStyles {
                for member in members {
                    print("Style for: \(dm.curFont) - \(member[1])")
                }
            }
        }
    }
}

func getFontStyles(for fontFamily: String) -> [String] {
     let fontManager = NSFontManager.shared

     guard let availableMembers = fontManager.availableMembers(ofFontFamily: fontFamily) else {
          return []
     }

     return availableMembers.compactMap { member in
         return member as? String
     }
}

Edit 1 #

补充代码中，我尝试在不同位置添加.onChange调用，但均未触发，代码如下：

struct AddFontItems: View {
var dm: DrawModel

init(_ dm: DrawModel ) { self.dm = dm }

var uniqueFontFamilies = NSFontManager.shared.availableFontFamilies.unique()

var body: some View {
    VStack {
        ForEach(uniqueFontFamilies, id: \.self) { curFont in
            Button( curFont) {
                dm.curFont = curFont
                print( "Set font to: " + dm.curFont )
            }
            .onChange( of: dm.curFont ) { // <--- here
                //          fontStyles = getFontStyles(for: dm.curFont)
                print( "In onChange1.1" )
            }
        }
        .onChange( of: dm.curFont ) { // <--- here
            //          fontStyles = getFontStyles(for: dm.curFont)
            print( "In onChange1.2" )
        }
        .onChange( of: dm.curFont ) { // <--- here
            //          fontStyles = getFontStyles(for: dm.curFont)
            print( "In onChange1.3" )
        }
    }
}
}

struct AddFontStyleItems: View {
    var dm: DrawModel
    init(_ dm: DrawModel ) { self.dm = dm }

    @State private var fontStyles: [String] = []        // reusable for .onAppear

    var body: some View {
        VStack {
            ForEach(fontStyles, id: \.self) { curStyle in
                Button(curStyle) {
                    dm.curFontStyle = curStyle
                    print("Set Style:\t \(dm.curFontStyle)")
                }
                .onChange( of: dm.curFont ) { // <--- here
                    fontStyles = getFontStyles(for: dm.curFont)
                    print( "In onChange2.1" )
                }
            }
            .onAppear { // TODO:  Called once on app launch.  Call on Font change
                fontStyles = getFontStyles(for: dm.curFont)
                print( "In onAppear" )
            }
            .onChange( of: dm.curFont ) { // <--- here
                fontStyles = getFontStyles(for: dm.curFont)
                print( "In onChange2.2" )
            }
        }
        .onChange( of: dm.curFont ) { // <--- here
            //          fontStyles = getFontStyles(for: dm.curFont)
            print( "In onChange2.3" )
        }
    }
}

func getFontStyles(for font: String) -> [String] {
    var justStyles: [String] = []
    if let fontInfo = NSFontManager.shared.availableMembers(ofFontFamily: font ) {
         for curFontInfo in fontInfo {
              if curFontInfo.count > 1 {
                  justStyles.append(curFontInfo[1] as? String ?? "")
              }
         }
    }
    return justStyles
}

内容的提问来源于stack exchange，提问作者Keith