iOS 15中如何为sheetPresentationController设置自定义Detents？有无替代方案？

iOS 15本身没有官方API支持自定义Sheet的detent高度，只能通过一些变通方式实现类似效果，给你几个靠谱的替代思路：

1. 自己封装带拖拽的自定义Sheet容器 #

放弃系统的sheetPresentationController，自己写一个模态弹窗容器，完全控制高度和交互逻辑：

• 先搞一个半透明背景的ViewController当容器，添加全屏的拖拽手势识别器
• 把你要展示的objVC作为子控制器加到容器里，初始把它的view高度设成550，贴底部布局
• 处理拖拽手势：根据手指偏移实时调整子view的高度，限制最小（比如550）和最大（屏幕高度）值
• 拖拽结束时做吸附逻辑，比如松手后回到550或者全屏，同时处理背景点击关闭的逻辑

简化代码示例：

// 自定义容器控制器
class CustomSheetContainerVC: UIViewController {
    private let contentVC: UIViewController
    private var contentViewHeightConstraint: NSLayoutConstraint!
    
    init(contentVC: UIViewController) {
        self.contentVC = contentVC
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .overFullScreen
        modalTransitionStyle = .crossDissolve
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupBackground()
        setupContentView()
        setupPanGesture()
    }
    
    private func setupBackground() {
        view.backgroundColor = UIColor.black.withAlphaComponent(0.5)
        let tap = UITapGestureRecognizer(target: self, action: #selector(dismissSheet))
        view.addGestureRecognizer(tap)
    }
    
    private func setupContentView() {
        addChild(contentVC)
        view.addSubview(contentVC.view)
        contentVC.didMove(toParent: self)
        
        contentVC.view.translatesAutoresizingMaskIntoConstraints = false
        contentViewHeightConstraint = contentVC.view.heightAnchor.constraint(equalToConstant: 550)
        NSLayoutConstraint.activate([
            contentVC.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            contentVC.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            contentVC.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            contentViewHeightConstraint
        ])
        contentVC.view.layer.cornerRadius = 22
        contentVC.view.clipsToBounds = true
    }
    
    private func setupPanGesture() {
        let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
        contentVC.view.addGestureRecognizer(pan)
    }
    
    @objc private func handlePan(_ gesture: UIPanGestureRecognizer) {
        let translation = gesture.translation(in: view)
        let newHeight = max(550, view.bounds.height + translation.y)
        
        switch gesture.state {
        case .changed:
            contentViewHeightConstraint.constant = newHeight
        case .ended:
            // 吸附逻辑：拖拽超过屏幕70%高度就全屏，否则回到550
            let shouldExpand = newHeight > view.bounds.height * 0.7
            contentViewHeightConstraint.constant = shouldExpand ? view.bounds.height : 550
            UIView.animate(withDuration: 0.3) {
                self.view.layoutIfNeeded()
            }
        default: break
        }
        gesture.setTranslation(.zero, in: view)
    }
    
    @objc private func dismissSheet() {
        dismiss(animated: true)
    }
}

// 使用方式：替换原来的sheet展示逻辑
// present(CustomSheetContainerVC(contentVC: objVC), animated: true)

2. 利用系统medium detent调整内容布局 #

如果不想自己写容器，可以利用iOS 15的.medium() detent，通过调整内容的内边距让视觉上达到自定义高度：

• 给objVC的view套一个scrollView或者contentView，把实际内容放在里面
• 设置contentView的高度为550，然后调整布局让contentView在medium sheet里居中显示
• 关闭sheet的滚动扩展，避免滚动触发sheet变大

修改你现有代码的else分支：

if let sheet = objVC?.sheetPresentationController {
    if #available(iOS 16.0, *) {
        sheet.detents = [
            .custom { _ in
                return 550
            }
        ]
    } else {
        sheet.detents = [.medium(), .large()]
        // 给objVC的内容做适配调整
        let contentView = UIView()
        contentView.backgroundColor = .white
        contentView.translatesAutoresizingMaskIntoConstraints = false
        objVC.view.addSubview(contentView)
        
        NSLayoutConstraint.activate([
            contentView.heightAnchor.constraint(equalToConstant: 550),
            contentView.leadingAnchor.constraint(equalTo: objVC.view.leadingAnchor),
            contentView.trailingAnchor.constraint(equalTo: objVC.view.trailingAnchor),
            contentView.centerYAnchor.constraint(equalTo: objVC.view.centerYAnchor)
        ])
        objVC.view.backgroundColor = .clear
    }
    sheet.largestUndimmedDetentIdentifier = .medium
    sheet.prefersGrabberVisible = true
    sheet.preferredCornerRadius = 22
    sheet.prefersScrollingExpandsWhenScrolledToEdge = false // iOS15下关闭滚动扩展
    sheet.prefersEdgeAttachedInCompactHeight = true
    sheet.widthFollowsPreferredContentSizeWhenEdgeAttached = true
    sheet.selectedDetentIdentifier = .medium        
}

3. 慎用私有API（不推荐） #

iOS 15的sheetPresentationController有私有方法可以设置自定义高度，但这种方法过审风险极高，而且系统版本更新可能直接崩溃，正式项目别碰，仅作技术参考。

内容的提问来源于stack exchange，提问作者tushar_b