将图像从 url 加载到 PictureBox答案

【问题标题】：Load an image from a url into a PictureBox将图像从 url 加载到 PictureBox
【发布时间】：2011-05-03 12:43:55
【问题描述】：

我想将图像加载到PictureBox。这是我要加载的图片：http://www.gravatar.com/avatar/6810d91caff032b202c50701dd3af745?d=identicon&r=PG

我该怎么做？

【问题讨论】：

还有什么问题/疑问？

【解决方案1】：

试试这个：

var request = WebRequest.Create("http://www.gravatar.com/avatar/6810d91caff032b202c50701dd3af745?d=identicon&r=PG");

using (var response = request.GetResponse())
using (var stream = response.GetResponseStream())
{
    pictureBox1.Image = Bitmap.FromStream(stream);
}

【讨论】：

这是一个很有帮助的例子。
如果您想在后台线程中下载图像，这是一个更好的解决方案。谢谢！

【解决方案2】：

PictureBox.Load(string url) 方法“将 ImageLocation 设置为指定的 URL 并显示指定的图像。”

【讨论】：

不幸的是，如果需要凭据，人们必须坚持另一种方法。

【解决方案3】：

yourPictureBox.ImageLocation = "http://www.gravatar.com/avatar/6810d91caff032b202c50701dd3af745?d=identicon&r=PG"

【讨论】：

【解决方案4】：

这是我使用的解决方案。我不记得为什么我不能只使用 PictureBox.Load 方法。我很确定这是因为我想将下载的图像正确缩放并居中到 PictureBox 控件中。如果我记得，PictureBox 上的所有缩放选项要么拉伸图像，要么调整 PictureBox 的大小以适合图像。我想要一个按我为 PictureBox 设置的大小正确缩放和居中的图像。

现在，我只需要制作一个异步版本...

这是我的方法：

   #region Image Utilities

    /// <summary>
    /// Loads an image from a URL into a Bitmap object.
    /// Currently as written if there is an error during downloading of the image, no exception is thrown.
    /// </summary>
    /// <param name="url"></param>
    /// <returns></returns>
    public static Bitmap LoadPicture(string url)
    {
        System.Net.HttpWebRequest wreq;
        System.Net.HttpWebResponse wresp;
        Stream mystream;
        Bitmap bmp;

        bmp = null;
        mystream = null;
        wresp = null;
        try
        {
            wreq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url);
            wreq.AllowWriteStreamBuffering = true;

            wresp = (System.Net.HttpWebResponse)wreq.GetResponse();

            if ((mystream = wresp.GetResponseStream()) != null)
                bmp = new Bitmap(mystream);
        }
        catch
        {
            // Do nothing... 
        }
        finally
        {
            if (mystream != null)
                mystream.Close();

            if (wresp != null)
                wresp.Close();
        }

        return (bmp);
    }

    /// <summary>
    /// Takes in an image, scales it maintaining the proper aspect ratio of the image such it fits in the PictureBox's canvas size and loads the image into picture box.
    /// Has an optional param to center the image in the picture box if it's smaller then canvas size.
    /// </summary>
    /// <param name="image">The Image you want to load, see LoadPicture</param>
    /// <param name="canvas">The canvas you want the picture to load into</param>
    /// <param name="centerImage"></param>
    /// <returns></returns>

    public static Image ResizeImage(Image image, PictureBox canvas, bool centerImage ) 
    {
        if (image == null || canvas == null)
        {
            return null;
        }

        int canvasWidth = canvas.Size.Width;
        int canvasHeight = canvas.Size.Height;
        int originalWidth = image.Size.Width;
        int originalHeight = image.Size.Height;

        System.Drawing.Image thumbnail =
            new Bitmap(canvasWidth, canvasHeight); // changed parm names
        System.Drawing.Graphics graphic =
                     System.Drawing.Graphics.FromImage(thumbnail);

        graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
        graphic.SmoothingMode = SmoothingMode.HighQuality;
        graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;
        graphic.CompositingQuality = CompositingQuality.HighQuality;

        /* ------------------ new code --------------- */

        // Figure out the ratio
        double ratioX = (double)canvasWidth / (double)originalWidth;
        double ratioY = (double)canvasHeight / (double)originalHeight;
        double ratio = ratioX < ratioY ? ratioX : ratioY; // use whichever multiplier is smaller

        // now we can get the new height and width
        int newHeight = Convert.ToInt32(originalHeight * ratio);
        int newWidth = Convert.ToInt32(originalWidth * ratio);

        // Now calculate the X,Y position of the upper-left corner 
        // (one of these will always be zero)
        int posX = Convert.ToInt32((canvasWidth - (image.Width * ratio)) / 2);
        int posY = Convert.ToInt32((canvasHeight - (image.Height * ratio)) / 2);

        if (!centerImage)
        {
            posX = 0;
            posY = 0;
        }
        graphic.Clear(Color.White); // white padding
        graphic.DrawImage(image, posX, posY, newWidth, newHeight);

        /* ------------- end new code ---------------- */

        System.Drawing.Imaging.ImageCodecInfo[] info =
                         ImageCodecInfo.GetImageEncoders();
        EncoderParameters encoderParameters;
        encoderParameters = new EncoderParameters(1);
        encoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality,
                         100L);

        Stream s = new System.IO.MemoryStream();
        thumbnail.Save(s, info[1],
                          encoderParameters);

        return Image.FromStream(s);
    }

    #endregion

这里是必需的包含。（其他代码可能需要一些，但为了安全起见包括所有）

using System.Windows.Forms;
using System.Drawing.Drawing2D;
using System.IO;
using System.Drawing.Imaging;
using System.Text.RegularExpressions;
using System.Drawing;

我一般如何使用它：

 ImageUtil.ResizeImage(ImageUtil.LoadPicture( "http://someurl/img.jpg", pictureBox1, true);

【讨论】：

您这里有很多资源没有正确处理，这是一种实用方法，因此它可能经常被调用：您应该添加适当的 using (var … = 或 .Dispose() 调用 - System.Drawing.Image、System.Drawing.Graphics、Bitmap 和 Stream 都实现了 IDisposable，因为它们处理非托管资源，所以如果你不明确释放它们，它可能会在以后再次咬你。

【解决方案5】：

如果您尝试在 form_load 中加载图像，最好使用代码

pictureBox1.LoadAsync(@"http://google.com/test.png");

不仅从网络加载，而且在您的表单加载中也没有延迟。

【讨论】：