SwiftUI/UIKit实现底部Sheet非Large档位回落效果的方法

SwiftUI 实现方案 #

原生SwiftUI的Sheet默认仅.large档位支持拖拽回落，要在其他档位实现该效果，需借助UIKit的UISheetPresentationController代理自定义 dismissal 逻辑：

1. 创建代理类处理回落逻辑

class SheetDelegate: NSObject, UISheetPresentationControllerDelegate {
    func presentationControllerDidAttemptToDismiss(_ presentationController: UIPresentationController) {
        guard let sheetController = presentationController as? UISheetPresentationController else { return }
        guard let currentDetent = sheetController.selectedDetentIdentifier else { return }
        
        // 非large档位时触发回落，这里以回落至medium为例
        if currentDetent != .large {
            sheetController.animateChanges {
                sheetController.selectedDetentIdentifier = .medium
            }
        } else {
            // large档位正常关闭Sheet
            presentationController.presentingViewController.dismiss(animated: true)
        }
    }
}

2. 在SwiftUI视图中注入代理

struct SheetProxy: UIViewControllerRepresentable {
    let delegate: SheetDelegate
    
    func makeUIViewController(context: Context) -> UIViewController {
        let vc = UIViewController()
        vc.modalPresentationStyle = .pageSheet
        vc.sheetPresentationController?.delegate = delegate
        return vc
    }
    
    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {}
}

struct ContentView: View {
    @State private var showing = false
    private let sheetDelegate = SheetDelegate()
    
    var body: some View {
        Button("Toggle") {
            showing.toggle()
        }
        .sheet(isPresented: $showing) {
            Text("Test sheet")
                .presentationDetents([.medium, .large])
                .background(SheetProxy(delegate: sheetDelegate))
        }
    }
}

UIKit 实现方案 #

直接基于UISheetPresentationController配置档位并实现代理：

class ViewController: UIViewController {
    private let sheetDelegate = SheetDelegate()
    
    @IBAction func toggleSheet(_ sender: UIButton) {
        let sheetVC = UIViewController()
        sheetVC.view.backgroundColor = .systemBackground
        sheetVC.modalPresentationStyle = .pageSheet
        
        if let sheetController = sheetVC.sheetPresentationController {
            sheetController.detents = [.medium(), .large()]
            sheetController.delegate = sheetDelegate
        }
        
        present(sheetVC, animated: true)
    }
}

// 复用之前的SheetDelegate类
class SheetDelegate: NSObject, UISheetPresentationControllerDelegate {
    func presentationControllerDidAttemptToDismiss(_ presentationController: UIPresentationController) {
        guard let sheetController = presentationController as? UISheetPresentationController else { return }
        guard let currentDetent = sheetController.selectedDetentIdentifier else { return }
        
        if currentDetent != .large {
            sheetController.animateChanges {
                sheetController.selectedDetentIdentifier = .medium
            }
        } else {
            presentationController.presentingViewController.dismiss(animated: true)
        }
    }
}

补充说明 #

• 若需自定义档位（如固定高度的Sheet），可使用UISheetPresentationController.Detent.custom()创建，在代理中匹配对应identifier即可调整回落目标。
• 回落动画通过系统animateChanges方法触发，与原生Sheet动画保持一致。

内容的提问来源于stack exchange，提问作者Gamekohl