如何修复iOS 15+中UIImagePickerController导航栏透明问题

问题现象 #

在iOS 15设备上使用UIImagePickerController，以overCurrentContext样式模态弹出相册时，组件导航栏背景变为透明，异常效果如下：

预期效果为导航栏保持白色，与iOS 15以下版本表现一致。直接在初始化picker后设置导航栏appearance的写法无法生效，原有无效代码参考：

let picker = UIImagePickerController()
picker.sourceType = .photoLibrary
picker.delegate = self
picker.modalPresentationStyle = .overCurrentContext
        
if #available(iOS 13.0, *) {
    let appearance = UINavigationBarAppearance()
    appearance.configureWithOpaqueBackground()
    appearance.backgroundColor = .white
    appearance.shadowColor = .white
    appearance.shadowImage = UIImage()
            
    picker.navigationBar.standardAppearance = appearance
    picker.navigationBar.scrollEdgeAppearance = appearance
}

viewController.present(picker, animated: true, completion: nil)

失效原因 #

代码不生效的核心原因是设置时机错误：UIImagePickerController会在自身viewDidLoad生命周期执行时，重置导航栏的外观配置，初始化后、present前设置的样式会被系统覆盖。同时iOS 15新增了紧凑尺寸下的滚动边缘导航栏样式属性，且overCurrentContext模态模式下，系统对半透明导航栏的渲染逻辑有调整，缺省配置会触发透明效果。

可行修复方案 #

推荐使用子类化方案，不会影响全局其他导航栏样式，稳定性最高：

1. 创建UIImagePickerController的子类，在viewWillAppear生命周期内强制设置导航栏样式

class WhiteStyleImagePicker: UIImagePickerController {
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        guard #available(iOS 13.0, *) else { return }
        let navAppearance = UINavigationBarAppearance()
        navAppearance.configureWithOpaqueBackground()
        navAppearance.backgroundColor = .white
        // 不需要分割线可以保留下面两行，需要的话删除即可
        navAppearance.shadowColor = .white
        navAppearance.shadowImage = UIImage()
        
        navigationBar.standardAppearance = navAppearance
        navigationBar.scrollEdgeAppearance = navAppearance
        navigationBar.compactAppearance = navAppearance
        if #available(iOS 15.0, *) {
            navigationBar.compactScrollEdgeAppearance = navAppearance
        }
        // 关键：关闭导航栏半透明，否则iOS15 overCurrentContext模式下仍会透明
        navigationBar.isTranslucent = false
    }
}

2. 调用时替换原有UIImagePickerController即可

let picker = WhiteStyleImagePicker()
picker.sourceType = .photoLibrary
picker.delegate = self
picker.modalPresentationStyle = .overCurrentContext
viewController.present(picker, animated: true)

如果不想创建子类，也可以把样式设置逻辑放到present的完成回调里执行，但是稳定性略低于子类方案：

let picker = UIImagePickerController()
picker.sourceType = .photoLibrary
picker.delegate = self
picker.modalPresentationStyle = .overCurrentContext

viewController.present(picker, animated: true) {
    guard #available(iOS 13.0, *) else { return }
    let navAppearance = UINavigationBarAppearance()
    navAppearance.configureWithOpaqueBackground()
    navAppearance.backgroundColor = .white
    navAppearance.shadowColor = .white
    navAppearance.shadowImage = UIImage()
    
    picker.navigationBar.standardAppearance = navAppearance
    picker.navigationBar.scrollEdgeAppearance = navAppearance
    picker.navigationBar.compactAppearance = navAppearance
    if #available(iOS 15.0, *) {
        picker.navigationBar.compactScrollEdgeAppearance = navAppearance
    }
    picker.navigationBar.isTranslucent = false
}

注意事项 #

• 必须将navigationBar.isTranslucent设置为false，否则即使配置了不透明的appearance，iOS15下overCurrentContext模式依然可能出现透明问题
• iOS15新增了compactScrollEdgeAppearance属性，对应横屏等紧凑尺寸场景下的滚动边缘导航栏样式，不配置会导致横屏时复现透明问题
• 不要在present之前直接修改picker的navigationBar样式，会被系统内部生命周期方法覆盖

内容的提问来源于stack exchange，提问作者Fadielse