C# 如何使用Silverlight 2计算加载图像的大小？

我正在将一个图像加载到背景中，我希望包含所有图像的silverlight画布能够调整到图像大小（或我确定的最大或最小值），无论图像大小如何。因此，我做了以下工作：

private int ImageMargin = 4;

    public Page()
    {
        InitializeComponent();

        BitmapImage bi = new BitmapImage(new Uri("1.jpg", UriKind.Relative));
        backgroundImage.Source = bi;
        bi.DownloadProgress += new EventHandler<DownloadProgressEventArgs>(bi_DownloadProgress);

        backgroundImage.SizeChanged += new SizeChangedEventHandler(backgroundImage_SizeChanged);

    }

    void bi_DownloadProgress(object sender, DownloadProgressEventArgs e)
    {
        if (e.Progress == 100)
        {
          LayoutRoot.Height = backgroundImage.Height + ImageMargin * 2;
          LayoutRoot.Width = backgroundImage.Width + ImageMargin * 2;
        }
    }

private int-ImageMargin=4；
公共网页（）
{
初始化组件（）；
BitmapImage bi=新的BitmapImage（新Uri（“1.jpg”，UriKind.Relative））；
backgroundImage.Source=bi；
bi.DownloadProgress+=新事件处理程序（bi_DownloadProgress）；
backgroundImage.SizeChanged+=新的SizeChangedEventHandler（backgroundImage\u SizeChanged）；
}
void bi_DownloadProgress（对象发送方，DownloadProgressEventArgs e）
{
如果（如进度==100）
{
LayoutRoot.Height=背景图像.Height+图像边距*2；
LayoutRoot.Width=背景图像.Width+图像边距*2；
}
}

图像加载正确，但无论我将backgroundImage.Height/Width（off.Loaded事件、.SizeChanged事件[1]，使用边框[2]等）放在何处，它总是返回0.0或NaN。我做错了什么

[1]

---

[2]

您可能需要等待一个UI循环周期，以确保Silverlight有机会更新布局。此外，您还必须确保图像实际上是可见的。我实际上写了一个小程序，从图像二进制文件中获取图像大小。缺点是您必须通过WebClient显式下载图像，但好处是您可以在不实际显示任何内容的情况下了解尺寸：

namespace StatMap.Silverlight.Services.UIHelpers
{
    public static class ImageSizeExtractor
    {
        public static bool TryGetImageSize(byte[] buf, out int width, out int height)
        {
            return TryGetPngSize(buf, out width, out height) || TryGetJpegSize(buf, out width, out height);
        }

        private static bool IsPng(byte[] buf)
        {
            return (buf.Length > 8)&&(buf[0] == 137) && (buf[1] == 80) && (buf[2] == 78) && (buf[3] == 71)
                   && (buf[4]==13)&&(buf[5]== 10)&&(buf[6]== 26)&&(buf[7]== 10);
        }

        private static bool TryGetPngSize(byte[] buf, out int width, out int height)
        {
            width = 0;
            height = 0;
            if (IsPng(buf))
            {
                int index = -1;
                for (int i = 8; i < buf.Length - 12;i++)
                {
                    if ((buf[i]==0x49)&&(buf[i+1]==0x48)&&(buf[i+2]==0x44)&&(buf[i+3]==0x52))
                    {
                        index = i + 4;
                        break;
                    }
                }

                if (index<0)
                {
                    return false;
                }
                width = buf[index + 3] + buf[index + 2]*256;
                height = buf[index + 7] + buf[index + 6]*256;
                return true;
            }
            return false;
        }

        private static bool TryGetJpegSize(byte[] buf, out int width, out int height)
        {
            //static char get_jpeg_size(unsigned char* data, unsigned int data_size, unsigned short *width, unsigned short *height) {
            //Check for valid JPEG image
            int i = 0; // Keeps track of the position within the file
            width = 0;
            height = 0;
            if (buf[i] == 0xFF && buf[i + 1] == 0xD8 && buf[i + 2] == 0xFF && buf[i + 3] == 0xE0)
            {
                i += 4;
                // Check for valid JPEG header (null terminated JFIF)
                if (buf[i + 2] == 'J' && buf[i + 3] == 'F' && buf[i + 4] == 'I' && buf[i + 5] == 'F' &&
                    buf[i + 6] == 0x00)
                {
                    //Retrieve the block length of the first block since the first block will not contain the size of file
                    int blockLength = buf[i]*256 + buf[i + 1];
                    while (i < buf.Length)
                    {
                        i += blockLength; //Increase the file index to get to the next block
                        if (i >= buf.Length) return false; //Check to protect against segmentation faults
                        if (buf[i] != 0xFF) return false; //Check that we are truly at the start of another block
                        if (buf[i + 1] == 0xC0)
                        {
                            //0xFFC0 is the "Start of frame" marker which contains the file size
                            //The structure of the 0xFFC0 block is quite simple [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
                            width = buf[i + 5]*256 + buf[i + 6];
                            height = buf[i + 7]*256 + buf[i + 8];
                            return true;
                        }
                        i += 2; //Skip the block marker
                        blockLength = buf[i]*256 + buf[i + 1]; //Go to the next block
                    }
                    return false; //If this point is reached then no size was found
                }
                return false;
            }
            return false;
        }
    }
}

namespace StatMap.Silverlight.Services.UIHelpers
{
公共静态类ImageSizeExtractor
{
公共静态bool TryGetImageSize（字节[]buf，out int width，out int height）
{
返回TryGetPngSize（buf，输出宽度，输出高度）| | TryGetPngSize（buf，输出宽度，输出高度）；
}
专用静态bool IsPng（字节[]buf）
{
返回值（buf.Length>8）&&（buf[0]==137）&&（buf[1]==80）&（buf[2]==78）&（buf[3]==71）
&&（buf[4]==13）&（buf[5]==10）&（buf[6]==26）&（buf[7]==10）；
}
专用静态bool TryGetPngSize（字节[]buf，out int width，out int height）
{
宽度=0；
高度=0；
如果（IsPng（buf））
{
int指数=-1；
对于（int i=8；i

---

希望这有帮助。

您可能需要等待一个UI循环周期，以确保Silverlight有机会更新布局。此外，您还必须确保图像实际上是可见的。我实际上写了一个小程序，从图像二进制文件中获取图像大小。缺点是您必须通过WebClient显式下载图像，但好处是您可以在不实际显示任何内容的情况下了解尺寸：

namespace StatMap.Silverlight.Services.UIHelpers
{
    public static class ImageSizeExtractor
    {
        public static bool TryGetImageSize(byte[] buf, out int width, out int height)
        {
            return TryGetPngSize(buf, out width, out height) || TryGetJpegSize(buf, out width, out height);
        }

        private static bool IsPng(byte[] buf)
        {
            return (buf.Length > 8)&&(buf[0] == 137) && (buf[1] == 80) && (buf[2] == 78) && (buf[3] == 71)
                   && (buf[4]==13)&&(buf[5]== 10)&&(buf[6]== 26)&&(buf[7]== 10);
        }

        private static bool TryGetPngSize(byte[] buf, out int width, out int height)
        {
            width = 0;
            height = 0;
            if (IsPng(buf))
            {
                int index = -1;
                for (int i = 8; i < buf.Length - 12;i++)
                {
                    if ((buf[i]==0x49)&&(buf[i+1]==0x48)&&(buf[i+2]==0x44)&&(buf[i+3]==0x52))
                    {
                        index = i + 4;
                        break;
                    }
                }

                if (index<0)
                {
                    return false;
                }
                width = buf[index + 3] + buf[index + 2]*256;
                height = buf[index + 7] + buf[index + 6]*256;
                return true;
            }
            return false;
        }

        private static bool TryGetJpegSize(byte[] buf, out int width, out int height)
        {
            //static char get_jpeg_size(unsigned char* data, unsigned int data_size, unsigned short *width, unsigned short *height) {
            //Check for valid JPEG image
            int i = 0; // Keeps track of the position within the file
            width = 0;
            height = 0;
            if (buf[i] == 0xFF && buf[i + 1] == 0xD8 && buf[i + 2] == 0xFF && buf[i + 3] == 0xE0)
            {
                i += 4;
                // Check for valid JPEG header (null terminated JFIF)
                if (buf[i + 2] == 'J' && buf[i + 3] == 'F' && buf[i + 4] == 'I' && buf[i + 5] == 'F' &&
                    buf[i + 6] == 0x00)
                {
                    //Retrieve the block length of the first block since the first block will not contain the size of file
                    int blockLength = buf[i]*256 + buf[i + 1];
                    while (i < buf.Length)
                    {
                        i += blockLength; //Increase the file index to get to the next block
                        if (i >= buf.Length) return false; //Check to protect against segmentation faults
                        if (buf[i] != 0xFF) return false; //Check that we are truly at the start of another block
                        if (buf[i + 1] == 0xC0)
                        {
                            //0xFFC0 is the "Start of frame" marker which contains the file size
                            //The structure of the 0xFFC0 block is quite simple [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
                            width = buf[i + 5]*256 + buf[i + 6];
                            height = buf[i + 7]*256 + buf[i + 8];
                            return true;
                        }
                        i += 2; //Skip the block marker
                        blockLength = buf[i]*256 + buf[i + 1]; //Go to the next block
                    }
                    return false; //If this point is reached then no size was found
                }
                return false;
            }
            return false;
        }
    }
}

namespace StatMap.Silverlight.Services.UIHelpers
{
公共静态类ImageSizeExtractor
{
公共静态bool TryGetImageSize（字节[]buf，out int width，out int height）
{
返回TryGetPngSize（buf，输出宽度，输出高度）| | TryGetPngSize（buf，输出宽度，输出高度）；
}
专用静态bool IsPng（字节[]buf）
{
返回值（buf.Length>8）&&（buf[0]==137）&&（buf[1]==80）&（buf[2]==78）&（buf[3]==71）
&&（buf[4]==13）&（buf[5]==10）&（buf[6]==26）&（buf[7]==10）；
}
专用静态bool TryGetPngSize（字节[]buf，out int width，out int height）
{
宽度=0；
高度=0；
如果（IsPng（buf））
{
int指数=-1；
对于（int i=8；i