当前，SwiftUI没有徽章功能，因此我们必须自定义。

参考文献HERE我创建了带有徽章的工作服

struct ContentView: View {
    private var badgePosition: CGFloat = 2
    private var tabsCount: CGFloat = 2
    @State var selectedView = 0
    var body: some View {
        GeometryReader { geometry in
            ZStack(alignment: .bottomLeading) {
                TabView {
                    Text("First View")
                        .tabItem {
                            Image(systemName: "list.dash")
                            Text("First")
                        }.tag(0)
                    Text("Second View")
                        .tabItem {
                            Image(systemName: "star")
                            Text("Second")
                        }.tag(1)
                }

                ZStack {
                  Circle()
                    .foregroundColor(.red)

                    Text("3")
                    .foregroundColor(.white)
                    .font(Font.system(size: 12))
                }
                .frame(width: 15,height: 15)
                .offset(x: ( ( 2 * self.badgePosition) - 0.95 ) * ( geometry.size.width / ( 2 * self.tabsCount ) ) + 2,y: -30)
                .opacity(1.0)
            }
        }
    }
}

 func calculateBadgeXPos(width: CGFloat) -> CGFloat {
        let t = (2*CGFloat(self.selectedTab))+1
        return CGFloat(t * width/(2*CGFloat(TABS_COUNT)))
    }

然后在这里使用它：

GeometryReader { geometry in
            ZStack(alignment: .bottomLeading) {
                // make sure to update TABS_COUNT
                TabView(selection: self.$selectedTab) {
                   ...
                }
                
                NotificationBadge(...)
                .offset(x: self.calculateBadgeXPos(width: geometry.size.width),y: -28)
            }
        }

在Preview上看起来像这样

现在在 SwiftUI 3 中，他们添加了 .badge() 修饰符

来源：HackingWithSwift

TabView {
    Text("Your home screen here")
        .tabItem {
            Label("Home",systemImage: "house")
        }
        .badge(5)
}

struct ContentView: View {
var body: some View {
    TabView {
        Text("Home")
            .tabItem {
                Text("Home")
            }
        
        Text("Home")
            .tabItem {
                Text("Home")
            }
        
        Text("Home")
            .tabItem {
                Text("Home")
            }
    }
    .introspectTabBarController { (tabbarController) in
        if let items = tabbarController.tabBar.items {
            let tabItem = items[2]
            tabItem.badgeValue = "1"
        }
    }
}

}