C# - object-oriented way of writing HTML as a string?

Question

Hi,

I'm trying to programmatically send an email of all of the dll files and their versions in a directory, recursively. I'd like to send the email as HTML output, using a table. Is there a good object-oriented way of doing this? I'd hate to write all of the tags by hand.

Something like:

private string getHTMLString()
{
    DirectoryInfo di = new DirectoryInfo("some directory");
    FileInfo[] files = di.GetFiles("*.dll", SearchOption.AllDirectories);
    foreach (FileInfo file in files)
    {
        Assembly assembly = Assembly.LoadFile(file.FullName);
        string version = assembly.GetName().Version.ToString();
    }
 }

Answer 1

Tags are tags. You'll have to write them.

You can use an HtmlTextWriter to do the actual writing, but there's no magical way to avoid that.

Answer 2

Something like this?

private string getHTMLString()
{
    DirectoryInfo di = new DirectoryInfo("some directory");
    FileInfo[] files = di.GetFiles("*.dll", SearchOption.AllDirectories);
    StringBuilder sb = new StringBuilder();
    sb.Append("<table>");
    foreach (FileInfo file in files)
    {
        Assembly assembly = Assembly.LoadFile(file.FullName);
        string version = assembly.GetName().Version.ToString();
        sb.AppendFormat("<tr><td>{0}</td><td>{1}</td></tr>", file.FullName, version);
    }
    sb.Append("</table>");
    return sb.ToString();

 }

Not really "object oriented" but I would argue the most logical.

DISCLAIMER: Compiled by hand

Answer 3

What you are doing seems simple enough to simply do it by hand with a string buffer. If this were more complicated I'd suggest you use a template engine such as StringTemplate.

Answer 4

You can use the XmlWriter to do this in a more OO-fashion:

StringBuilder sb = new StringBuilder();
XmlWriter xmlWri = XmlWriter.Create(sb);
xmlWri.WriteStartElement("html");
{
    xmlWri.WriteStartElement("body");
    {
        xmlWri.WriteAttributeString("bgcolor", "black");

        // More html stuff
    }
    xmlWri.WriteEndElement(); // body
}
xmlWri.WriteEndElement(); // html
xmlWri.Flush();
xmlWri.Close();
string html = sb.ToString();

Edit: It does get rather cumbersome to do this, and in the future if you want to change the HTML content you'll have to do it by code. A better way is to read in a pre-formatted HTML document with place-holders that map to the columns in the table, so all you'd need is a way to loop through all the columns and do a find/replace against the place-holders in the HTML document.

Answer 5

You can actually use the HtmlTextWriter and use the HtmlTextWriterTag enum to create the tags, without actually having to hand write the "<" and ">".

Example:

StringBuilder sb = new StringBuilder();

using (HtmlTextWriter w = new HtmlTextWriter(new StringWriter(sb)))
{
      w.RenderBeginTag(HtmlTextWriterTag.P);

      w.AddStyleAttribute(HtmlTextWriterStyle.Color, "red");

      w.RenderBeginTag(HtmlTextWriterTag.Span);

      w.Write("This is some text");

      w.RenderEndTag();

      w.RenderEndTag();
 }

 string html = sb.ToString();

It doesn't automatically create the HTML for you, but it does help you write HTML in a "more OO" way and it will help you (not ensure) write valid HTML (all tags have closing tags, etc).

Answer 6

I am not certain that you need an OO approach. Is your intent to create a table with a column that contains the directory of the dll, or will you add a column for each level of sub directory that you traverse?

bdowden has a nice solution that you could use with mletterle approach - you could always wrap this is a class, but I think that's overkill.

Answer 7

It might be overkill, but you can use LINQ to XML to generate your HTML string... Here's your code, using LINQ and XElement to generate a simple table.

The only thing you need to be careful of is empty tags that are not valid as self-closing tags in HTML. For example, an empty TD: new XElement("td") will render as <td/> which is not valid HTML. You can fix this by inserting an empty string as content: new XElement("td", String.Empty) - this will output <td></td>.

private string GetHtmlString()
{
    DirectoryInfo di = new DirectoryInfo("some directory");
    FileInfo[] files = di.GetFiles("*.dll", SearchOption.AllDirectories);

    var container = new XElement("table",
        from file in files
        let assembly = Assembly.LoadFile(file.FullName)
        select new XElement("tr", 
            new XElement("td", file.FullName),
            new XElement("td", assembly.GetName().Version.ToString())
        )
    );

    return container.ToString();
 }

Answer 8

You can do it OO by instantiating a System.Web.UI.WebControls.Table, adding TableRows and TableCells and then calling Table.RenderControl into an HtmlTextWriter, but to be fair: That would suck :)

        var tbl = new System.Web.UI.WebControls.Table();

        DirectoryInfo di = new DirectoryInfo("some directory");
        FileInfo[] files = di.GetFiles("*.dll", SearchOption.AllDirectories);
        foreach (FileInfo file in files)
        {
            Assembly assembly = Assembly.LoadFile(file.FullName);
            string version = assembly.GetName().Version.ToString();

            var tr = new System.Web.UI.WebControls.TableRow();
            var tc = new System.Web.UI.WebControls.TableCell();
            tc.Text = HttpUtility.HtmlEncode(version);
            tr.Cells.Add(tc);
            tbl.Rows.Add(tr);
        }

        using (var ts = new StringWriter())
        using (var html = new System.Web.UI.HtmlTextWriter(ts))
        {
            // Not entirely sure about this part
            tbl.RenderControl(html);
            html.Flush();
            string htmlString = ts.ToString();
        }