tvOS中UITabBarItem能否为聚焦和选中状态设置不同背景色？

系统原生的UITabBarAppearance的selectionIndicatorTintColor属性会同时作用于聚焦和选中两种状态，无法直接通过该属性单独配置两种状态的颜色，也没有公开的UITabBarItemAppearance属性可以像配置文字颜色一样直接分状态设置指示器背景色，但可以通过以下两种方案实现需求。

方案1：监听焦点变化动态切换颜色（轻量实现） #

通过重写聚焦更新回调，判断当前视图是否聚焦在TabBarItem上，动态修改选中指示器的颜色：

override func didUpdateFocus(in context: UIFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {
    super.didUpdateFocus(in: context, with: coordinator)
    
    let isFocusOnTabItem = { (view: UIView?) -> Bool in
        guard let view = view else { return false }
        return NSStringFromClass(type(of: view)).contains("UITabBarButton")
    }
    
    if isFocusOnTabItem(context.nextFocusedView) {
        // 聚焦状态设置半透明紫色，可自行调整参数
        tabBar.standardAppearance.selectionIndicatorTintColor = .purple.withAlphaComponent(0.7)
    } else if isFocusOnTabItem(context.previouslyFocusedView) {
        // 选中非聚焦状态设置实色紫色
        tabBar.standardAppearance.selectionIndicatorTintColor = .purple
    }
}

该方案实现成本低，无需修改现有TabBar结构，适合快速适配需求。

方案2：自定义选中指示器（稳定兼容） #

如果不想依赖系统私有类名判断，需要更高的兼容性和自定义空间，可以禁用系统原生指示器，自己添加自定义视图控制颜色和位置：

1. 先禁用系统原生选中指示器

tabBar.standardAppearance.selectionIndicatorTintColor = .clear

2. 添加自定义指示器视图并存储约束

private let customIndicator: UIView = {
    let view = UIView()
    view.layer.cornerRadius = 8 // 可按需调整圆角
    view.clipsToBounds = true
    view.translatesAutoresizingMaskIntoConstraints = false
    return view
}()
private var indicatorLeadingConst: NSLayoutConstraint?
private var indicatorWidthConst: NSLayoutConstraint?

// 在视图加载完成后添加指示器到TabBar
override func viewDidLoad() {
    super.viewDidLoad()
    tabBar.insertSubview(customIndicator, at: 0)
    indicatorLeadingConst = customIndicator.leadingAnchor.constraint(equalTo: tabBar.leadingAnchor)
    indicatorWidthConst = customIndicator.widthAnchor.constraint(equalToConstant: 0)
    NSLayoutConstraint.activate([
        indicatorLeadingConst!,
        indicatorWidthConst!,
        customIndicator.centerYAnchor.constraint(equalTo: tabBar.centerYAnchor),
        customIndicator.heightAnchor.constraint(equalToConstant: 50) // 按需调整高度
    ])
}

3. 封装指示器更新方法，在选中和聚焦回调中调用

private func updateIndicator(for item: UITabBarItem, isFocused: Bool) {
    guard let itemIndex = tabBar.items?.firstIndex(of: item),
          let tabButtons = tabBar.subviews.filter({ NSStringFromClass(type(of: $0)).contains("UITabBarButton") }),
          itemIndex < tabButtons.count else { return }
    
    let targetButton = tabButtons[itemIndex]
    indicatorLeadingConst?.constant = targetButton.frame.minX
    indicatorWidthConst?.constant = targetButton.frame.width
    customIndicator.backgroundColor = isFocused ? .purple.withAlphaComponent(0.7) : .purple
    
    UIView.animate(withDuration: 0.25) {
        self.tabBar.layoutIfNeeded()
    }
}

// 选中Tab时调用
func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
    updateIndicator(for: item, isFocused: false)
}

// 焦点变化时调用
override func didUpdateFocus(in context: UIFocusUpdateContext, with coordinator: UIFocusAnimationCoordinator) {
    super.didUpdateFocus(in: context, with: coordinator)
    guard let selectedItem = tabBar.selectedItem else { return }
    
    let isFocusOnTab = NSStringFromClass(type(of: context.nextFocusedView ?? UIView())).contains("UITabBarButton")
    updateIndicator(for: selectedItem, isFocused: isFocusOnTab)
}

该方案完全自主控制指示器的样式，除了颜色外还可以自定义圆角、阴影、动画效果等，适配性更强。

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