XML Editor Control

• Download source on GitHub

If you have a Windows Forms application that involves XML editing or viewing, you can use this control to save yourself the effort of formatting the XML content. For now, only syntax highlighting is implemented. I expect to add more features in the future like spacing, grouping, intellisense, etc…

Usage

Simply add the files (XmlToken.cs, XmlTokenizer.cs, XmlEditor.cs, XmlEditor.designer.cs) to your project, then drag and drop the XmlEditor control from the Toolbox into your Windows Form.

The XmlEditor control currently has three public properties. Use AllowXmlFormatting to enable or disable formatting on the XML content in the editor. The ReadOnly property tells whether or not to allow the user to change the text. The Text property sets or gets the text of the XMLeditor.

Here is how the control looks like when AllowXmlFormatting = true and ReadOnly = false (default values):

Implementation

To color the XML string, we have to split it into multiple tokens, then color each token based on its type. I have identified the following token types (based on syntax highlighting behavior in Visual Studio 2008):

• A “Value” is anything between double quotes
• A “Comment” is anything that starts with <!– and ends with –> (or starts with <!– and is never closed with –>)
• An “Element” is any letter or digit that falls between < and a space or >
• An “Attribute” is any letter or digit that falls after a < followed by space and not closed by >
• An “Escape” is anything that starts with & and ends with ; (For example &quote;)
• A “SpecialChar” is any character that is not a letter or a digit
• A “None” is anything else

The Tokenize() public static method of the XmlTokenizer class does the job of splitting a string into XML tokens.

An XmlToken object is a representation of an XML token with details about the exact text of that token, its location in the string and its type.

Here is the code in the XmlEditor control that does the syntax highlighting:

List<XmlToken> tokens = XmlTokenizer.Tokenize(xmlEditor.Text);

foreach (XmlToken token in tokens)
{
    xmlEditor.Select(token.Index, token.Text.Length);

    switch (token.Type)
    {
        case XmlTokenType.Attribute:
            xmlEditor.SelectionColor = Color.Red;
            break;
        case XmlTokenType.Comment:
            xmlEditor.SelectionColor = Color.DarkGreen;
            break;

        //  and so on for the other token types
    }
}

You can look at the code on my GitHub page.

Filed under: csharp, WinForms, XML

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