• 1、基本数据模型定义

//使用枚举的方式定义数据
enum TabBarItem: Hashable {
    case home, favorites, profile, messages
    //图标
    var iconName: String {
        switch self {
        case .home: return "house"
        case .favorites: return "heart"
        case .profile: return "person"
        case .messages: return "message"
        }
    }
    //标题
    var title: String {
        switch self {
        case .home: return "Home"
        case .favorites: return "Favorites"
        case .profile: return "Profile"
        case .messages: return "Messages"
        }
    }
    //颜色
    var color: Color {
        switch self {
        case .home: return Color.blue
        case .favorites: return Color.red
        case .profile: return Color.green
        case .messages: return Color.orange
        }
    }
}

• 2、抽象tabbar全屏内容容器（两种样式）

//自定义Tabbr全屏内容容器
struct CustomTabBarContainerView<Content:View>: View {
    //选中的tabbar模块
    @Binding var selection: TabBarItem
    //tabbar选项内容
    let content: Content
    //tabbar具体选项个数
    @State private var tabs: [TabBarItem] = []
    
    init(selection: Binding<TabBarItem>, @ViewBuilder content: () -> Content) {
        self._selection = selection
        self.content = content()
    }
    
    var body: some View {
        ZStack(alignment: .bottom) {
              //全屏内容
                content
                .ignoresSafeArea()
            //Tabbar选项容器
            CustomTabBarView(tabs: tabs, selection: $selection, localSelection: selection)
            } //: ZSTACK
        //通过preferenceKey和tabBarItem方法联动方式动态变化tabbar个数
        .onPreferenceChange(TabBarItemsPreferenceKey.self) { value in
            self.tabs = value
        }
    }
}

//预览代码
struct CustomTabBarContainerView_Previews: PreviewProvider {
    
    static let tabs: [TabBarItem] = [
        .home, .favorites, .profile, .messages
    ]
    
    static var previews: some View {
        CustomTabBarContainerView(selection: .constant(tabs.first!)) {
            Color.red
        }
    }
}

• 3、抽象tabbar选项内容容器

struct CustomTabBarView: View {
    // MARK: -  属性
    let tabs: [TabBarItem]
    @Binding  var selection: TabBarItem
    @Namespace private var namespace
    //用于动画
    @State var localSelection: TabBarItem
    
    // MARK: -  内容
    var body: some View {
        // tabBarVersionOne
        tabBarVersionTwo
            .onChange(of: selection) { newValue in
                withAnimation(.easeInOut) {
                    localSelection = newValue
                }
            }
    }
}

//预览代码
struct CustomTabBarView_Previews: PreviewProvider {
    static let tabs: [TabBarItem] = [
        .home, .favorites, .profile
    ]
    static var previews: some View {
        VStack {
            Spacer()
            CustomTabBarView(tabs: tabs, selection: .constant(tabs.first!), localSelection: tabs.first!)
        }
    }
}

// MARK: -  扩展
//样式1
extension CustomTabBarView {
    private func tabView(tab: TabBarItem) -> some View {
        VStack {
            Image(systemName: tab.iconName)
                .font(.subheadline)
            Text(tab.title)
                .font(.system(size: 10, weight: .semibold, design: .rounded))
        } //: VSTACK
        .foregroundColor(selection == tab ? tab.color : Color.gray)
        .padding(.vertical, 8)
        .frame(maxWidth: .infinity)
        .background(selection == tab ? tab.color.opacity(0.2) : Color.clear)
        .cornerRadius(10)
    }
    
    private var tabBarVersionOne: some View {
        HStack {
            ForEach(tabs, id: \.self) { tab in
                tabView(tab: tab)
                    .onTapGesture {
                        switchToTab(tab: tab)
                    }
            }
        } //: HSTACK
        .padding(6)
        .background(Color.white.ignoresSafeArea(edges: .bottom))
    }
    
    private func switchToTab(tab: TabBarItem) {
            selection = tab
    }
}

// 样式2
extension CustomTabBarView {
    private func tabView2(tab: TabBarItem) -> some View {
        VStack {
            Image(systemName: tab.iconName)
                .font(.subheadline)
            Text(tab.title)
                .font(.system(size: 10, weight: .semibold, design: .rounded))
        } //: VSTACK
        .foregroundColor(localSelection == tab ? tab.color : Color.gray)
        .padding(.vertical, 8)
        .frame(maxWidth: .infinity)
        .background(
            ZStack {
                if localSelection == tab {
                    RoundedRectangle(cornerRadius: 10)
                        .fill(tab.color.opacity(0.2))
                        .matchedGeometryEffect(id: "background_rectangle", in: namespace)
                }
            } //: ZSTACK
        )
    }
    
    private var tabBarVersionTwo: some View {
        HStack {
            ForEach(tabs, id: \.self) { tab in
                tabView2(tab: tab)
                    .onTapGesture {
                        switchToTab(tab: tab)
                    }
            }
        } //: HSTACK
        .padding(6)
        .background(Color.white.ignoresSafeArea(edges: .bottom))
        .cornerRadius(10)
        .shadow(color: Color.black.opacity(0.3), radius: 10, x: 0, y: 5)
        .padding(.horizontal)
    }
    
}

• 4、使用preferenceKey累计记录tabberItem

// MARK: -  创建 PreferenceKey
struct TabBarItemsPreferenceKey: PreferenceKey {
    
    static var defaultValue: [TabBarItem] = []
    
    static func reduce(value: inout [TabBarItem], nextValue: () -> [TabBarItem]) {
        value += nextValue()
    }
}

// MARK: -  创建Modifier
struct TabBarItemViewModifier: ViewModifier {
    let tab: TabBarItem
    @Binding var selection: TabBarItem
    
    func body(content: Content) -> some View {
        content
            .opacity(selection == tab ? 1.0 : 0.0)
            .preference(key: TabBarItemsPreferenceKey.self, value: [tab])
    }
}

// MARK: -  扩展添加tabbar选项的方式
extension View {
    func tabBarItem(tab: TabBarItem, selection: Binding<TabBarItem>) -> some View {
        self
            .modifier(TabBarItemViewModifier(tab: tab, selection: selection))
    }
}

• 5、使用例子

struct AppTabBarView: View {
    // MARK: -  属性
    @State private var selection: String = "home"
    @State private var tabSelection: TabBarItem = .home
    // MARK: -  内容
    var body: some View {
        CustomTabBarContainerView(selection: $tabSelection) {
            Color.blue
                .tabBarItem(tab: .home, selection: $tabSelection)
            
            Color.red
                .tabBarItem(tab: .favorites, selection: $tabSelection)
            
            Color.green
                .tabBarItem(tab: .profile, selection: $tabSelection)
            
            Color.orange
                .tabBarItem(tab: .messages, selection: $tabSelection)
        }
    }
}

• 6、效果图
  样式1
  

  ![
  tabbarTwo.gif
  ]
  样式2
  
  tabbar.gif

github例子：https://github.com/dennie-lee/SwiftUICustomTabBar
说明：未经许可不可转载