iOS中NSAttributedString添加竖图保存后水平翻转的问题

在iOS开发中，使用NSTextAttachment调整NSAttributedString内的图片大小时，遇到竖版图片保存后变为横版的问题——图片缩放功能正常，但添加到NSAttributedString后出现莫名水平翻转。

问题根源 #

1. 原图片缩放方法使用UIGraphicsBeginImageContext，未处理图片的imageOrientation属性，导致图片方向信息丢失，绘制后方向异常。
2. NSTextAttachment未设置正确的bounds，仅设置image无法保证图片的显示和存储尺寸与方向匹配。

修改后的代码实现 #

1. 修复UIImage缩放扩展（处理方向）

extension UIImage {
    func resizeImage(scale: CGFloat) -> UIImage {
        let newSize = CGSize(width: size.width * scale, height: size.height * scale)
        
        UIGraphicsBeginImageContextWithOptions(newSize, false, UIScreen.main.scale)
        defer { UIGraphicsEndImageContext() }
        
        let transform = transformForOrientation(newSize)
        draw(in: CGRect(origin: .zero, size: newSize).applying(transform))
        
        return UIGraphicsGetImageFromCurrentImageContext()!
    }
    
    private func transformForOrientation(_ newSize: CGSize) -> CGAffineTransform {
        var transform = CGAffineTransform.identity
        
        switch imageOrientation {
        case .down, .downMirrored:
            transform = transform.translatedBy(x: newSize.width, y: newSize.height)
            transform = transform.rotated(by: .pi)
        case .left, .leftMirrored:
            transform = transform.translatedBy(x: newSize.width, y: 0)
            transform = transform.rotated(by: .pi / 2)
        case .right, .rightMirrored:
            transform = transform.translatedBy(x: 0, y: newSize.height)
            transform = transform.rotated(by: -.pi / 2)
        case .up, .upMirrored:
            break
        @unknown default:
            break
        }
        
        switch imageOrientation {
        case .upMirrored, .downMirrored:
            transform = transform.translatedBy(x: newSize.width, y: 0)
            transform = transform.scaledBy(x: -1, y: 1)
        case .leftMirrored, .rightMirrored:
            transform = transform.translatedBy(x: newSize.height, y: 0)
            transform = transform.scaledBy(x: -1, y: 1)
        case .up, .down, .left, .right:
            break
        @unknown default:
            break
        }
        
        return transform
    }
}

2. 优化NSAttributedString扩展（设置Attachment Bounds）

extension NSAttributedString {
    func attributedStringWithResizedImages(with maxWidth: CGFloat) -> NSAttributedString {
        let text = NSMutableAttributedString(attributedString: self)
        text.enumerateAttribute(.attachment, in: NSRange(location: 0, length: text.length), options: []) { value, range, stop in
            guard let attachment = value as? NSTextAttachment else { return }
            
            guard let image = attachment.image(forBounds: attachment.bounds, textContainer: NSTextContainer(), characterIndex: range.location) else { return }
            
            guard image.size.width > maxWidth else { return }
            
            let scale = maxWidth / image.size.width
            let newImage = image.resizeImage(scale: scale)
            
            let newAttachment = NSTextAttachment()
            newAttachment.image = newImage
            // 设置正确的bounds，确保图片显示尺寸匹配
            newAttachment.bounds = CGRect(origin: .zero, size: newImage.size)
            
            text.addAttribute(.attachment, value: newAttachment, range: range)
        }
        return text
    }
}

3. 保存与读取逻辑（无需修改）

原保存和读取代码可继续使用，RTFD格式会正确存储设置好的attachment信息：

func saveAttributedTextToUserDefault(attributedText: NSAttributedString, key: String) {
    do {
        let data = try attributedText.data(from: NSRange(location: 0, length: attributedText.length), documentAttributes: [.documentType: NSAttributedString.DocumentType.rtfd])
        userDefault.set(data, forKeyPath: myNotes)
    } catch {
        print(error)
    }
}

func getAttributedTextFromUserDefault(key: String) -> NSAttributedString {
    if let dataValue = userDefault.data(forKey: myNotes) as? Data {
        do {
            let attributeText = try NSAttributedString(data: dataValue, documentAttributes: nil)
            return attributeText
        } catch {
            print("error: ", error)
        }
    }
    return NSAttributedString()
}

关键修复说明 #

• 新增transformForOrientation方法，根据图片的原始方向计算绘制变换，确保缩放后图片方向与原图一致。
• 使用UIGraphicsBeginImageContextWithOptions替代UIGraphicsBeginImageContext，支持Retina屏幕，避免图片模糊。
• 为新创建的NSTextAttachment设置bounds，确保图片在AttributedString中的显示尺寸和存储信息准确。

内容的提问来源于stack exchange，提问作者Dian