Code to strip out <p> tags in empty placeholders

Once in a while the question how to strip <p> and <span> tags in empty placeholders comes up in the newsgroup.

A solution would be to implement a custom placeholder control that removes these tags or a workflow event.

The simplest solution is a workflow event to do this. This event would have to check if there is meaningful content in the control and if not ensure that an empty string is set a placeholder content.

Something like this:

public void CmsPosting_PlaceholderPropertyChanging( Object sender, PropertyChangingEventArgs e )
{
   if (e.Target is HtmlPlaceholder)
   {
      if (IsEmpty(e.PropertyValue))
          e.PropertyValue = "";
   }
}

private bool IsEmpty(string content)
{
    //visible tags
    string tagsToKeep = "img|hr";

    //This regular expression matches all tags listed above
    string regExpTagsToKeep =
        "<[\\s|/]*(" + tagsToKeep + ")\\b[^>]*>";
    Regex reTagsToKeep = new Regex(regExpTagsToKeep, RegexOptions.IgnoreCase | RegexOptions.Compiled);

    //Check if one of the tags to keep is included and exit.
    if (reTagsToKeep.IsMatch(content))
    {
        //Placeholder is not empty.
        return false;
    }

    //This regular expression gets all tags in the content
    string regExpForAllTags = "<[^>]*>";
    Regex reAllTags = new Regex(regExpForAllTags, RegexOptions.IgnoreCase | RegexOptions.Compiled);

    //Remove all Tags by replacing with an empty string
    content = reAllTags.Replace(content, "");

    //Remove all spaces and non-breaking spaces ( )
    content = content.Replace(" ","");
    content = content.Replace(" ","");

    if (content == "")
    {
        //All tags removed, we are left with an empty string
        //Placeholder is empty.
        return true;
    }
    else
    {
        //After removing all tags, we still have content.
        //Placeholder is not empty.
        return false;
    }
}