Drop images from IE

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Introduction

In a recent project I found the need to be able to drop an image from Internet Explorer onto my form and capture the URL of the image. If you have tried using any of the text formats to get the drop data then you know this does not work. At best you will get the locally cached path of the image file. There is little or no documentation on the subject, and attempting to search for information only yields others seeking the same answers. This is why I decided to make this an article. Note that this code makes use of regular expressions. As this is not an article about regex's, which is a huge topic in itself, I provide no explanation of the expressions used. You can easily find numerous tutorials on Regular Expressions.

Background

The key to reading the source URL of the image is in the data type. Through much trial and error, I found that the magic words are "HTML Format", as you will see below.

Using the code

Simply place the appropriate code below into your DragEnter and DragDrop events, add the required functions and that's all.

The DragEnter event would look as such:

private void myControl_DragEnter(object sender, DragEventArgs e)
{
  if (e.Data.GetDataPresent("HTML Format"))
    e.Effect = DragDropEffects.Copy;
}

To actually capture the URL, place the following in the DragDrop event:

private void myControl_DragDrop(object sender, DragEventArgs e)
{
  string clipboardHtml = (string)e.Data.GetData("HTML Format");
  string htmlFragment = getHtmlFragment(clipboardHtml);
  string imageSrc = parseImageSrc(htmlFragment);
  string baseURL = parseBaseURL(clipboardHtml);

  if (imageSrc.ToUpper().IndexOf("HTTP://") == 0)
    MessageBox.Show(imageSrc);
  else
    MessageBox.Show(baseURL + imageSrc.Substring(1));
}

We need the if statement in the above because the base URL may or may not be included in the image tag.

There are three supporting functions:

• getHtmlFragment: Retrieves the complete image tag, including width, alt text, etc.
• parseImageSrc: Retrieves the path of the image itself. The path is only relative so the next function is needed still.
• parseBaseURL: Retrieves the base URL as the name implies.

string getHtmlFragment(string clipboardHtml)
{
  int fragStartPos = int.Parse(Regex.Match(clipboardHtml, 
    @"^StartFragment:(\d+)", RegexOptions.Multiline).Groups[1].Value);
  int fragEndPos = int.Parse(Regex.Match(clipboardHtml, 
    @"^EndFragment:(\d+)", RegexOptions.Multiline).Groups[1].Value);
  return clipboardHtml.Substring(fragStartPos, fragEndPos - fragStartPos);
}

string parseImageSrc(string html)
{
  return Regex.Match(html, @"<img.*?src=[""'](.*?)[""'].*>", 
    RegexOptions.IgnoreCase | RegexOptions.Singleline).Groups[1].Value;
}

string parseBaseURL(string html)
{
  return Regex.Match(html, @http://.*?/, 
        RegexOptions.IgnoreCase).Groups[0].Value;
}

Points of Interest

Check out the demo project to see it in action.

History

• Original posting - June 10, 2007