Xamarin.iOS中MediaPicker.CapturePhotoAsync拍照图片旋转问题求助

我正在使用Xamarin.Essentials框架调用相机拍照，使用了MediaPicker.CapturePhotoAsync()方法，代码如下：

async Task CatchPhoto()
{
    var photo = await MediaPicker.CapturePhotoAsync();
    if (photo == null)
    {
        return;
    }
    await LoadPhotoAsync(photo);
}

async Task LoadPhotoAsync(FileResult photo)
{
    if(photo == null)
    {
       PhotoPath = null;
       return;
    }

    var newFile = Path.Combine(FileSystem.CacheDirectory, photo.FileName);

    using (var stream = await photo.OpenReadAsync())
    using (var newStream = File.OpenWrite(newFile))
        await stream.CopyToAsync(newStream);

    PhotoPath = newFile;

    UIImage image =  UIImage.FromFile(PhotoPath);
    // 此图片为旋转后的图片
    if(image != null)
    {
        if(image.Orientation == UIImageOrientation.Up)
            image = new UIImage(image.CGImage, 1.0f, UIImageOrientation.Right);
    }
}

当前代码在竖屏模式下可正常处理图片方向，但横屏模式下拍照时，上述解决方案失效。请问有什么解决办法？或者有没有其他方法可避免图片旋转？

解决办法 #

方法1：统一消除图片方向标记依赖 #

硬编码判断UIImageOrientation.Up仅适配竖屏场景，横屏时可通过绘图上下文生成无方向信息的图片，彻底消除方向标记影响：

修改LoadPhotoAsync中的图片处理逻辑：

async Task LoadPhotoAsync(FileResult photo)
{
    if(photo == null)
    {
       PhotoPath = null;
       return;
    }

    var newFile = Path.Combine(FileSystem.CacheDirectory, photo.FileName);

    using (var stream = await photo.OpenReadAsync())
    using (var newStream = File.OpenWrite(newFile))
        await stream.CopyToAsync(newStream);

    PhotoPath = newFile;

    UIImage image = UIImage.FromFile(PhotoPath);
    if(image != null)
    {
        UIGraphics.BeginImageContextWithOptions(image.Size, false, image.CurrentScale);
        image.Draw(CGRect.Empty);
        var correctedImage = UIGraphics.GetImageFromCurrentImageContext();
        UIGraphics.EndImageContext();
        image = correctedImage;
    }
}

方法2：基于EXIF自动修正方向 #

使用第三方库SixLabors.ImageSharp读取图片EXIF方向标签并自动修正，无需手动判断设备状态：

1. 先安装NuGet包SixLabors.ImageSharp
2. 修改代码：

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Processing;

async Task LoadPhotoAsync(FileResult photo)
{
    if(photo == null)
    {
       PhotoPath = null;
       return;
    }

    var newFile = Path.Combine(FileSystem.CacheDirectory, "fixed_" + photo.FileName);

    using (var stream = await photo.OpenReadAsync())
    using (var image = Image.Load(stream))
    {
        image.Mutate(x => x.AutoOrient());
        await image.SaveAsync(newFile);
    }

    PhotoPath = newFile;
    UIImage image = UIImage.FromFile(PhotoPath);
}

方法3：完善方向判断逻辑 #

如果不想依赖第三方库，可针对UIImage.Orientation的所有可能值做完整判断，覆盖横屏及其他场景：

if(image != null)
{
    switch(image.Orientation)
    {
        case UIImageOrientation.Up:
            break;
        case UIImageOrientation.Right:
            image = new UIImage(image.CGImage, 1.0f, UIImageOrientation.Down);
            break;
        case UIImageOrientation.Left:
            image = new UIImage(image.CGImage, 1.0f, UIImageOrientation.Up);
            break;
        case UIImageOrientation.Down:
            image = new UIImage(image.CGImage, 1.0f, UIImageOrientation.Left);
            break;
        default:
            image = new UIImage(image.CGImage, 1.0f, UIImageOrientation.Up);
            break;
    }
}

内容的提问来源于stack exchange，提问作者Swati