如何在UISheetPresentationController中移除背景暗化并保留点击关闭功能？

我使用UISheetPresentationController展示视图，代码如下：

@IBAction func click(_ sender: Any) {
    let whiteViewController = WhiteViewController.instanceFromMainStoryBoard()
    
    if let sheet = whiteViewController.sheetPresentationController {
        sheet.detents = [.medium()]
        
        sheet.prefersScrollingExpandsWhenScrolledToEdge = false
        
        sheet.prefersGrabberVisible = false
        
        // Remove dim effect.
        ////sheet.largestUndimmedDetentIdentifier = .medium
    }
    
    self.present(whiteViewController, animated: true)
}

当前实现的特性：

• 背景暗化
• 点击任意位置可关闭视图
  

但我需要移除背景暗化，同时保留点击关闭功能。当添加sheet.largestUndimmedDetentIdentifier = .medium后，背景暗化消失，但点击关闭功能也失效了：

请问有没有办法同时实现这两个需求？

解决方案 #

方法1：自定义透明背景+点击手势 #

通过给Sheet添加全屏透明背景视图，手动实现点击关闭逻辑，同时用largestUndimmedDetentIdentifier移除系统暗化：

@IBAction func click(_ sender: Any) {
    let whiteViewController = WhiteViewController.instanceFromMainStoryBoard()
    
    if let sheet = whiteViewController.sheetPresentationController {
        sheet.detents = [.medium()]
        sheet.prefersScrollingExpandsWhenScrolledToEdge = false
        sheet.prefersGrabberVisible = false
        // 移除系统背景暗化
        sheet.largestUndimmedDetentIdentifier = .medium
        
        // 添加全屏透明点击背景
        let tapBackground = UIView(frame: UIScreen.main.bounds)
        tapBackground.backgroundColor = .clear
        // 把背景放在Sheet内容下方
        whiteViewController.view.insertSubview(tapBackground, at: 0)
        
        // 添加点击手势关闭Sheet
        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(dismissPresentedSheet))
        tapBackground.addGestureRecognizer(tapGesture)
    }
    
    self.present(whiteViewController, animated: true)
}

@objc private func dismissPresentedSheet() {
    dismiss(animated: true)
}

方法2：修改系统暗化视图透明度 #

保留系统默认的点击关闭逻辑，在Sheet展示后找到系统的暗化背景视图，将其设为透明：

@IBAction func click(_ sender: Any) {
    let whiteViewController = WhiteViewController.instanceFromMainStoryBoard()
    
    if let sheet = whiteViewController.sheetPresentationController {
        sheet.detents = [.medium()]
        sheet.prefersScrollingExpandsWhenScrolledToEdge = false
        sheet.prefersGrabberVisible = false
        
        self.present(whiteViewController, animated: true) { [weak self] in
            // 递归查找系统暗化背景视图
            func findDimView(in view: UIView) -> UIView? {
                let alpha = view.backgroundColor?.cgColor.alpha ?? 0
                if alpha > 0 && alpha < 1 {
                    return view
                }
                for subview in view.subviews {
                    if let dimView = findDimView(in: subview) {
                        return dimView
                    }
                }
                return nil
            }
            
            guard let window = self?.view.window, let dimView = findDimView(in: window) else { return }
            dimView.backgroundColor = .clear
        }
    }
}

注意点 #

• 方法2依赖系统视图层级，苹果后续更新可能导致失效，稳定性不如方法1
• 方法1需确保透明背景视图覆盖全屏，避免出现点击无响应的区域

内容的提问来源于stack exchange，提问作者Cheok Yan Cheng