UIDocumentPickerController分屏模式下取消按钮不显示问题求助

1. 强制设置文档选择器的全屏展示样式 #

默认情况下，UIDocumentPickerController会根据当前尺寸类自动调整展示逻辑，在50/50、70/30这类中等宽度分屏模式下，可能因导航栏布局挤压导致取消按钮被隐藏。直接强制设置其为全屏展示，可确保导航栏元素完整显示：

let documentPicker = UIDocumentPickerViewController(forOpeningContentTypes: [.pdf])
documentPicker.modalPresentationStyle = .fullScreen
documentPicker.delegate = self
present(documentPicker, animated: true)

2. 自定义子类修复导航栏布局约束 #

若需要保留弹窗样式而非强制全屏，可以通过自定义UIDocumentPickerController子类，给取消按钮添加最小宽度约束，避免被窄屏挤压：

class FixedDocumentPicker: UIDocumentPickerViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        navigationController?.navigationBar.prefersLargeTitles = false
        // 给取消按钮添加最小宽度约束
        if let cancelBtn = navigationItem.leftBarButtonItem {
            cancelBtn.widthAnchor.constraint(greaterThanOrEqualToConstant: 65).isActive = true
        }
    }
}

使用时直接初始化自定义类即可：

let picker = FixedDocumentPicker(forOpeningContentTypes: [.pdf])
picker.modalPresentationStyle = .popover
picker.popoverPresentationController?.sourceView = triggerButton
picker.popoverPresentationController?.sourceRect = triggerButton.bounds
present(picker, animated: true)

3. 监听尺寸类变化动态调整 #

通过监听界面尺寸类变化，在分屏模式切换时强制更新导航栏布局：

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    guard traitCollection.horizontalSizeClass != previousTraitCollection?.horizontalSizeClass else { return }
    // 强制导航栏重新布局，确保按钮显示
    navigationController?.navigationBar.setNeedsLayout()
    navigationController?.navigationBar.layoutIfNeeded()
}

4. 针对特定iOS版本适配 #

部分iOS版本（如iOS 15及更早）在分屏模式下对UIDocumentPicker的布局存在系统级bug，可针对版本做差异化处理：

let documentPicker = UIDocumentPickerViewController(forOpeningContentTypes: [.pdf])
if #available(iOS 16.0, *) {
    documentPicker.modalPresentationStyle = .pageSheet
} else {
    documentPicker.modalPresentationStyle = .fullScreen
}
documentPicker.delegate = self
present(documentPicker, animated: true)

内容的提问来源于stack exchange，提问作者Konstantin