如何使用C＃正确创建缩略图？

Question

我在Core .NET 2.2框架的顶部有一个使用C#编写的控制台应用程序。

我想创建异步任务，该任务会将完整大小的图像写入存储。 此外，该过程将需要创建缩略图并将其写入默认存储。

遵循的是处理逻辑的方法。 我记录了每一行以解释我相信正在发生

// This method accepts FileObject and returns a task
// The generated task will write the file as is to the default storage
// Then it'll create a thumbnail of that images and store it to the default storage
public async Task ProcessImage(FileObject file, int thumbnailWidth = 250)
{
    // The name of the full-size image
    string filename = string.Format("{0}{1}", file.ObjectId, file.Extension);

    // The name along with the exact path to the full-size image
    string path = Path.Combine(file.ContentId, filename);

    // Write the full-size image to the storage
    await Storage.CreateAsync(file.Content, path)
                 .ContinueWith(task =>
    {
        // Reset the stream to the beginning since this will be the second time the stream is read
        file.Content.Seek(0, SeekOrigin.Begin);

        // Create original Image
        Image image = Image.FromStream(file.Content);

        // Calulate the height of the new thumbnail
        int height = (thumbnailWidth * image.Height) / image.Width;

        // Create the new thumbnail
        Image thumb = image.GetThumbnailImage(thumbnailWidth, height, null, IntPtr.Zero);

        using (MemoryStream thumbnailStream = new MemoryStream())
        {
            // Save the thumbnail to the memory stream
            thumb.Save(thumbnailStream, image.RawFormat);

            // The name of the new thumbnail
            string thumbnailFilename = string.Format("thumbnail_{0}", filename);

            // The name along with the exact path to the thumbnail
            string thumbnailPath = Path.Combine(file.ContentId, thumbnailFilename);

            // Write the thumbnail to storage
            Storage.CreateAsync(thumbnailStream, thumbnailPath);
        }

        // Dispose the file object to ensure the Stream is disposed
        file.Dispose();
        image.Dispose();
        thumb.Dispose();
    });
}

如果需要，这是我的FileObject

public class FileObject : IDisposable
{
    public string ContentId { get; set; }
    public string ObjectId { get; set; }
    public ContentType ContentType { get; set; }
    public string Extension { get; set; }
    public Stream Content { get; set; }
    private bool IsDisposed;

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (IsDisposed)
            return;

        if (disposing && Content != null)
        {
            Content.Close();
            Content.Dispose();
        }

        IsDisposed = true;
    }
}

上面的代码将正确的全尺寸图像写入存储驱动器。 它还会将缩略图写入存储。 但是，缩略图始终会损坏。 换句话说，生成的缩略图文件始终以0字节写入。

将相同的流写入存储后，如何从file.Content流正确创建缩略图？

Answer 1

我找出问题的原因。 由于某种原因，行thumb.Save(thumbnailStream, image.RawFormat); 将thumbnailStream放置在末尾，并且在写入存储时不会写入任何内容

解决该问题的方法是在像这样写入流后重置搜索位置

    using (MemoryStream thumbnailStream = new MemoryStream())
    {
        // Save the thumbnail to the memory stream
        thumb.Save(thumbnailStream, image.RawFormat);

        // Reset the seek position to the begining
        thumbnailStream.Seek(0, SeekOrigin.Begin);

        // The name of the new thumbnail
        string thumbnailFilename = string.Format("thumbnail_{0}", filename);

        // The name along with the exact path to the thumbnail
        string thumbnailPath = Path.Combine(file.ContentId, thumbnailFilename);

        // Write the thumbnail to storage
        Storage.CreateAsync(thumbnailStream, thumbnailPath);
    }

我不确定在复制到新流中后thumb.Save(...)不会将位置重置为0会有什么好处！ 我只是觉得应该这样做，因为它将始终编写一个新的流，而不是将其追加到现有的流之后。