GDI读取后上载文件锁

Question

我有以下ImageObject类:

public class ImageObject
{
    public static Image CropImage(Image img, Rectangle cropArea)
    {
        Bitmap bmpImage = new Bitmap(img);
        Bitmap target = new Bitmap(cropArea.Width, cropArea.Height);
        using(Graphics g = Graphics.FromImage(target))
        {
            g.DrawImage(bmpImage, new Rectangle(0, 0, target.Width, target.Height), cropArea, GraphicsUnit.Pixel);
            g.Dispose();
        }
        return (Image)target;
    }

    public static Image ResizeImage(Image imgToResize, Size size)
    {
        int sourceWidth = imgToResize.Width;
        int sourceHeight = imgToResize.Height;

        float nPercent = 0;
        float nPercentW = 0;
        float nPercentH = 0;

        nPercentW = ((float)size.Width / (float)sourceWidth);
        nPercentH = ((float)size.Height / (float)sourceHeight);

        if (nPercentH < nPercentW)
            nPercent = nPercentH;
        else
            nPercent = nPercentW;

        int destWidth = (int)(sourceWidth * nPercent);
        int destHeight = (int)(sourceHeight * nPercent);

        Bitmap b = new Bitmap(destWidth, destHeight);
        //Graphics g = Graphics.FromImage((Image)b);
        using(Graphics g = Graphics.FromImage((Image)b))
        {
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
            g.Dispose();    
        }
        return (Image)b;
    }

    public static void SaveJpeg(string path, System.Drawing.Image source, long quality)
    {
        EncoderParameter qualityParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        ImageCodecInfo jpegCodec = GetEncoderInfo("image/jpeg");
        if (jpegCodec == null)
            return;
        EncoderParameters encoderParams = new EncoderParameters(1);
        encoderParams.Param[0] = qualityParam;
        source.Save(path, jpegCodec, encoderParams);
    }

    private static ImageCodecInfo GetEncoderInfo(string mimeType)
    {
        // Get image codecs for all image formats
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();

        // Find the correct image codec
        for (int i = 0; i < codecs.Length; i++)
            if (codecs[i].MimeType == mimeType)
                return codecs[i];
        return null;
    }
}

我从另一个类的函数中引用此代码:

public static void CreateAvatar(string filepath, int x, int y, int w, int h)
{
    var big = filepath + "100x100.jpg";
    var medium = filepath + "40x40.jpg";
    var small = filepath + "25x25.jpg";
    var full_path = filepath + "avatar.jpg";
    var temp_path = filepath + "avatar_t.jpg";

    if (File.Exists(big))
    {
        File.Delete(big);
    }
    if (File.Exists(medium))
    {
        File.Delete(medium);
    }
    if (File.Exists(small))
    {
        File.Delete(small);
    }
    if (File.Exists(temp_path))
    {
        File.Delete(temp_path);
    }

    System.Drawing.Image img = System.Drawing.Image.FromFile(full_path);
    System.Drawing.Rectangle rect = new Rectangle(x, y, w, h);
    System.Drawing.Size hundred = new Size(100, 100);
    System.Drawing.Size forty = new Size(40, 40);
    System.Drawing.Size twentyfive = new Size(25, 25);

    //we crop, then we resize...
    var cropped = ImageObject.CropImage(img, rect);
    ImageObject.SaveJpeg(temp_path, cropped, 100L);

    //problems usually from here. can't save big, because it can't read temp_path - it's locked...
    var resize_big = ImageObject.ResizeImage(System.Drawing.Image.FromFile(temp_path), hundred);
    ImageObject.SaveJpeg(big, resize_big, 100L);

    var resize_forty = ImageObject.ResizeImage(System.Drawing.Image.FromFile(temp_path), forty);
    ImageObject.SaveJpeg(medium, resize_forty, 100L);

    var resize_twentyfive = ImageObject.ResizeImage(System.Drawing.Image.FromFile(temp_path), twentyfive);
    ImageObject.SaveJpeg(small, resize_twentyfive, 100L);
}

此方法由Web服务调用.在第一次执行此代码时(在IIS重新启动之后),一切都很好,但如果再次使用它会挂起.我知道它与我创建的两个图像有关:avatar.jpg和avatar_t.jpg.我知道这是因为我无法在资源管理器中删除或重命名图像:

我已经确保我已经按照许多人的建议使用了Dispose这些Graphics物品,但是我无法弄清楚为什么锁不会释放？有谁能看到这个问题？

理想情况下,我想在底部执行此操作:

var resize_twentyfive = ImageObject.ResizeImage(System.Drawing.Image.FromFile(temp_path), twentyfive);
            ImageObject.SaveJpeg(small, resize_twentyfive, 100L);

//clean up, delete avatar.jpg and avatar_t.jpg
File.Delete(temp_path);
File.Delete(full_path);

并删除我以前读取的图像 - 不再需要它们.我不介意他们留在那里,只要我可以随意从上传者覆盖他们......

Answer 1

System.Drawing.Image.FromFile() 在图像上调用Dispose之前不会关闭文件.

位图和图像构造函数依赖项:

当从文件构造Bitmap对象或Image对象时,该文件在对象的生命周期内保持锁定状态.因此,您无法更改图像并将其保存回原始位置的同一文件中.

此外,如果在Bitmap对象的生命周期中销毁了流,则无法成功访问基于流的图像.例如,在销毁流后,Graphics.DrawImage()函数可能不会成功

Image.FromFile()是一种非常糟糕的API方法(从某种意义上说它会让开发人员失败!).问题是由以下原因引起的:

GDI +以及System.Drawing命名空间可以推迟原始图像位的解码,直到图像需要这些位.另外,即使在图像被解码之后,GDI +也可以确定丢弃用于大位图的存储器并且稍后重新解码更有效.因此,GDI +必须能够在Bitmap或Image对象的生命周期内访问图像的源位.

为了保持对源位的访问,GDI +锁定任何源文件,并强制应用程序在Bitmap或Image对象的生命周期内维持任何源流​​的生命周期.

再次引用支持文章:

若要解决此问题,请使用以下方法之一创建新的位图图像(如本节后面所述):

• 创建非索引图像.
• 创建索引图像.

在这两种情况下,在原始位图上调用Bitmap.Dispose()方法会删除文件上的锁定,或者删除流或内存保持活动的要求.