iPad端FormSheet样式Sheet不遵循preferedContentSize问题咨询

核心实现思路 #

按设备尺寸类分支处理：

• 紧凑尺寸类（iPhone）：用UISheetPresentationController配置自定义detents实现底部Sheet
• 常规尺寸类（iPad）：强制使用FormSheet悬浮样式，通过修改布局约束实现近乎全屏效果，忽略preferredContentSize

代码实现 #

1. 通用Sheet展示工具方法 #

func presentCustomSheet(_ targetVC: UIViewController, from presenter: UIViewController) {
    switch presenter.traitCollection.horizontalSizeClass {
    case .compact:
        targetVC.modalPresentationStyle = .pageSheet
        guard let sheet = targetVC.sheetPresentationController else {
            presenter.present(targetVC, animated: true)
            return
        }
        // 自定义detents：半屏+全屏，可按需调整
        sheet.detents = [
            .custom(resolver: { $0.maximumDetentValue * 0.5 }),
            .large()
        ]
        sheet.prefersGrabberVisible = true
    default:
        targetVC.modalPresentationStyle = .formSheet
        targetVC.modalTransitionStyle = .coverVertical
        targetVC.presentationController?.delegate = presenter
    }
    
    presenter.present(targetVC, animated: true)
}

2. 实现代理调整iPad布局 #

在负责展示的ViewController中添加代理扩展：

extension YourPresenterVC: UIAdaptivePresentationControllerDelegate {
    func adaptivePresentationStyle(for controller: UIPresentationController, traitCollection: UITraitCollection) -> UIModalPresentationStyle {
        return .none // 保留FormSheet样式，禁止系统自动适配
    }
    
    func presentationControllerDidPresent(_ presentationController: UIPresentationController) {
        guard let presentedView = presentationController.presentedViewController.view,
              let container = presentationController.containerView else { return }
        
        // 清除原有尺寸约束
        presentedView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.deactivate(presentedView.constraints)
        
        // 设置新约束，仅留边距（此处设为20pt，可修改）
        let edgeMargin: CGFloat = 20
        NSLayoutConstraint.activate([
            presentedView.leadingAnchor.constraint(equalTo: container.leadingAnchor, constant: edgeMargin),
            presentedView.trailingAnchor.constraint(equalTo: container.trailingAnchor, constant: -edgeMargin),
            presentedView.topAnchor.constraint(equalTo: container.topAnchor, constant: edgeMargin),
            presentedView.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: -edgeMargin)
        ])
    }
}

3. 注意事项 #

• iPad端必须设置modalPresentationStyle = .formSheet，才能保证弹窗悬浮显示
• 通过presentationControllerDidPresent修改约束，直接覆盖系统基于preferredContentSize生成的布局
• 紧凑尺寸类的detents可根据需求增减档位或调整比例

内容的提问来源于stack exchange，提问作者Warpling