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ArthurHub/ClipboardHelper.cs

Last active June 21, 2023 07:50
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Helper class for setting HTML and plain text formatting to clipboard (http://theartofdev.com/2014/06/12/setting-htmltext-to-clipboard-revisited/)
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ClipboardHelper.cs
/// <summary>
/// Helper to encode and set HTML fragment to clipboard.<br/>
/// See http://theartofdev.com/2014/06/12/setting-htmltext-to-clipboard-revisited/.<br/>
/// <seealso cref="CreateDataObject"/>.
/// </summary>
/// <remarks>
/// The MIT License (MIT) Copyright (c) 2014 Arthur Teplitzki.
/// </remarks>
public static class ClipboardHelper
{
#region Fields and Consts
/// <summary>
/// The string contains index references to other spots in the string, so we need placeholders so we can compute the offsets. <br/>
/// The <![CDATA[<<<<<<<]]>_ strings are just placeholders. We'll back-patch them actual values afterwards. <br/>
/// The string layout (<![CDATA[<<<]]>) also ensures that it can't appear in the body of the html because the <![CDATA[<]]> <br/>
/// character must be escaped. <br/>
/// </summary>
private const string Header = @"Version:0.9
StartHTML:<<<<<<<<1
EndHTML:<<<<<<<<2
StartFragment:<<<<<<<<3
EndFragment:<<<<<<<<4
StartSelection:<<<<<<<<3
EndSelection:<<<<<<<<4";
/// <summary>
/// html comment to point the beginning of html fragment
/// </summary>
public const string StartFragment = "<!--StartFragment-->";
/// <summary>
/// html comment to point the end of html fragment
/// </summary>
public const string EndFragment = @"<!--EndFragment-->";
/// <summary>
/// Used to calculate characters byte count in UTF-8
/// </summary>
private static readonly char[] _byteCount = new char[1];
#endregion
/// <summary>
/// Create <see cref="DataObject"/> with given html and plain-text ready to be used for clipboard or drag and drop.<br/>
/// Handle missing <![CDATA[<html>]]> tags, specified start\end segments and Unicode characters.
/// </summary>
/// <remarks>
/// <para>
/// Windows Clipboard works with UTF-8 Unicode encoding while .NET strings use with UTF-16 so for clipboard to correctly
/// decode Unicode string added to it from .NET we needs to be re-encoded it using UTF-8 encoding.
/// </para>
/// <para>
/// Builds the CF_HTML header correctly for all possible HTMLs<br/>
/// If given html contains start/end fragments then it will use them in the header:
/// <code><![CDATA[<html><body><!--StartFragment-->hello <b>world</b><!--EndFragment--></body></html>]]></code>
/// If given html contains html/body tags then it will inject start/end fragments to exclude html/body tags:
/// <code><![CDATA[<html><body>hello <b>world</b></body></html>]]></code>
/// If given html doesn't contain html/body tags then it will inject the tags and start/end fragments properly:
/// <code><![CDATA[hello <b>world</b>]]></code>
/// In all cases creating a proper CF_HTML header:<br/>
/// <code>
/// <![CDATA[
/// Version:1.0
/// StartHTML:000000177
/// EndHTML:000000329
/// StartFragment:000000277
/// EndFragment:000000295
/// StartSelection:000000277
/// EndSelection:000000277
/// <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
/// <html><body><!--StartFragment-->hello <b>world</b><!--EndFragment--></body></html>
/// ]]>
/// </code>
/// See format specification here: http://msdn.microsoft.com/library/default.asp?url=/workshop/networking/clipboard/htmlclipboard.asp
/// </para>
/// </remarks>
/// <param name="html">a html fragment</param>
/// <param name="plainText">the plain text</param>
public static DataObject CreateDataObject(string html, string plainText)
{
html = html ?? String.Empty;
var htmlFragment = GetHtmlDataString(html);
// re-encode the string so it will work correctly (fixed in CLR 4.0)
if (Environment.Version.Major < 4 && html.Length != Encoding.UTF8.GetByteCount(html))
htmlFragment = Encoding.Default.GetString(Encoding.UTF8.GetBytes(htmlFragment));
var dataObject = new DataObject();
dataObject.SetData(DataFormats.Html, htmlFragment);
dataObject.SetData(DataFormats.Text, plainText);
dataObject.SetData(DataFormats.UnicodeText, plainText);
return dataObject;
}
/// <summary>
/// Clears clipboard and sets the given HTML and plain text fragment to the clipboard, providing additional meta-information for HTML.<br/>
/// See <see cref="CreateDataObject"/> for HTML fragment details.<br/>
/// </summary>
/// <example>
/// ClipboardHelper.CopyToClipboard("Hello <b>World</b>", "Hello World");
/// </example>
/// <param name="html">a html fragment</param>
/// <param name="plainText">the plain text</param>
public static void CopyToClipboard(string html, string plainText)
{
var dataObject = CreateDataObject(html, plainText);
Clipboard.SetDataObject(dataObject, true);
}
/// <summary>
/// Generate HTML fragment data string with header that is required for the clipboard.
/// </summary>
/// <param name="html">the html to generate for</param>
/// <returns>the resulted string</returns>
private static string GetHtmlDataString(string html)
{
var sb = new StringBuilder();
sb.AppendLine(Header);
sb.AppendLine(@"<!DOCTYPE HTML PUBLIC ""-//W3C//DTD HTML 4.0 Transitional//EN"">");
// if given html already provided the fragments we won't add them
int fragmentStart, fragmentEnd;
int fragmentStartIdx = html.IndexOf(StartFragment, StringComparison.OrdinalIgnoreCase);
int fragmentEndIdx = html.LastIndexOf(EndFragment, StringComparison.OrdinalIgnoreCase);
// if html tag is missing add it surrounding the given html (critical)
int htmlOpenIdx = html.IndexOf("<html", StringComparison.OrdinalIgnoreCase);
int htmlOpenEndIdx = htmlOpenIdx > -1 ? html.IndexOf('>', htmlOpenIdx) + 1 : -1;
int htmlCloseIdx = html.LastIndexOf("</html", StringComparison.OrdinalIgnoreCase);
if (fragmentStartIdx < 0 && fragmentEndIdx < 0)
{
int bodyOpenIdx = html.IndexOf("<body", StringComparison.OrdinalIgnoreCase);
int bodyOpenEndIdx = bodyOpenIdx > -1 ? html.IndexOf('>', bodyOpenIdx) + 1 : -1;
if (htmlOpenEndIdx < 0 && bodyOpenEndIdx < 0)
{
// the given html doesn't contain html or body tags so we need to add them and place start/end fragments around the given html only
sb.Append("<html><body>");
sb.Append(StartFragment);
fragmentStart = GetByteCount(sb);
sb.Append(html);
fragmentEnd = GetByteCount(sb);
sb.Append(EndFragment);
sb.Append("</body></html>");
}
else
{
// insert start/end fragments in the proper place (related to html/body tags if exists) so the paste will work correctly
int bodyCloseIdx = html.LastIndexOf("</body", StringComparison.OrdinalIgnoreCase);
if (htmlOpenEndIdx < 0)
sb.Append("<html>");
else
sb.Append(html, 0, htmlOpenEndIdx);
if (bodyOpenEndIdx > -1)
sb.Append(html, htmlOpenEndIdx > -1 ? htmlOpenEndIdx : 0, bodyOpenEndIdx - (htmlOpenEndIdx > -1 ? htmlOpenEndIdx : 0));
sb.Append(StartFragment);
fragmentStart = GetByteCount(sb);
var innerHtmlStart = bodyOpenEndIdx > -1 ? bodyOpenEndIdx : (htmlOpenEndIdx > -1 ? htmlOpenEndIdx : 0);
var innerHtmlEnd = bodyCloseIdx > -1 ? bodyCloseIdx : (htmlCloseIdx > -1 ? htmlCloseIdx : html.Length);
sb.Append(html, innerHtmlStart, innerHtmlEnd - innerHtmlStart);
fragmentEnd = GetByteCount(sb);
sb.Append(EndFragment);
if (innerHtmlEnd < html.Length)
sb.Append(html, innerHtmlEnd, html.Length - innerHtmlEnd);
if (htmlCloseIdx < 0)
sb.Append("</html>");
}
}
else
{
// handle html with existing start\end fragments just need to calculate the correct bytes offset (surround with html tag if missing)
if (htmlOpenEndIdx < 0)
sb.Append("<html>");
int start = GetByteCount(sb);
sb.Append(html);
fragmentStart = start + GetByteCount(sb, start, start + fragmentStartIdx) + StartFragment.Length;
fragmentEnd = start + GetByteCount(sb, start, start + fragmentEndIdx);
if (htmlCloseIdx < 0)
sb.Append("</html>");
}
// Back-patch offsets (scan only the header part for performance)
sb.Replace("<<<<<<<<1", Header.Length.ToString("D9"), 0, Header.Length);
sb.Replace("<<<<<<<<2", GetByteCount(sb).ToString("D9"), 0, Header.Length);
sb.Replace("<<<<<<<<3", fragmentStart.ToString("D9"), 0, Header.Length);
sb.Replace("<<<<<<<<4", fragmentEnd.ToString("D9"), 0, Header.Length);
return sb.ToString();
}
/// <summary>
/// Calculates the number of bytes produced by encoding the string in the string builder in UTF-8 and not .NET default string encoding.
/// </summary>
/// <param name="sb">the string builder to count its string</param>
/// <param name="start">optional: the start index to calculate from (default - start of string)</param>
/// <param name="end">optional: the end index to calculate to (default - end of string)</param>
/// <returns>the number of bytes required to encode the string in UTF-8</returns>
private static int GetByteCount(StringBuilder sb, int start = 0, int end = -1)
{
int count = 0;
end = end > -1 ? end : sb.Length;
for (int i = start; i < end; i++)
{
_byteCount[0] = sb[i];
count += Encoding.UTF8.GetByteCount(_byteCount);
}
return count;
}
}
@it3xl
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it3xl commented Apr 22, 2021 •
edited
Loading

The second trouble is that you .NET process may be more fast than the Windows Clipboard.
I can't realyze why but it constantly a promlbes on some machines.

So, we just need to add a check.

Clipboard.Clear();
ClipboardHelper.CopyToClipboard(myHtmlPart);

then use somethign from the following to check

contains = Clipboard.ContainsData(DataFormats.Html);
// contains = Clipboard.ContainsText(TetxtDataFormat.Html);

And to deley

Task.Delay(TimeSpan.FromMillisecons(1))
    .Wait();

For example, for VSTO projects you'll get the following error

System.Runtime.InteropServices.COMException (0x800A11FD): 
This method or property is not available because the Clipboard is empty or not valid.

at Microsoft.Office.Interop.Word.Range.PasteSpecial(Object& IconIndex, Object& Link, Object& Placement, Object& DisplayAsIcon, Object& DataType, Object& IconFileName, Object& IconLabel)

I'll try to provide my entire checking code later after some testing.
In my code I also check that a pasting text is exactly the same as in the Clipboard.

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