HtmlTextWriter - Adding multiple classes to a tag

Question

What is the best way to add multiple classes to a tag using HtmlTextWriter?

What I would like to do is something like...

 writer.AddAttribute(HtmlTextWriterAttribute.Class, "Class1");
 writer.AddAttribute(HtmlTextWriterAttribute.Class, "Class2");
 writer.RenderBeginTag(HtmlTextWriterTag.Table);

Resulting in...

<table class="Class1 Class2">

I appreciate I could do...

writer.AddAttribute(HtmlTextWriterAttribute.Class, "Class1 Class2");

However it isn't always this straightforward when building the control dynamically. Are there alternative ways to "append" classes to the tag?

Answer 1

why not extend the writer class and add a AddClass and RemoveClass methods on it which while rendering uses all added class names. Internally you could use a List _classNames to hold then and later just join them

writer.AddAttribute(HtmlTextWriterAttribute.Class,string.Join(_classNames.ToArray(), " ");

Hope that helps!

Answer 2

Just following the previous post idea....

public class NavHtmlTextWritter : HtmlTextWriter
{
    private Dictionary<HtmlTextWriterAttribute, List<string>> attrValues = new Dictionary<HtmlTextWriterAttribute, List<string>>();
    private HtmlTextWriterAttribute[] multiValueAttrs = new[] { HtmlTextWriterAttribute.Class };

    public NavHtmlTextWritter (TextWriter writer) : base(writer) { } 

    public override void AddAttribute(HtmlTextWriterAttribute key, string value)
    {
        if (multiValueAttrs.Contains(key))
        {
            if (!this.attrValues.ContainsKey(key))
                this.attrValues.Add(key, new List<string>());

            this.attrValues[key].Add(value);
        }
        else
        {
            base.AddAttribute(key, value);
        }
    }

    public override void RenderBeginTag(HtmlTextWriterTag tagKey)
    {
        this.addMultiValuesAttrs();
        base.RenderBeginTag(tagKey);
    }

    public override void RenderBeginTag(string tagName)
    {
        this.addMultiValuesAttrs();
        base.RenderBeginTag(tagName);
    }

    private void addMultiValuesAttrs()
    {
        foreach (var key in this.attrValues.Keys)
            this.AddAttribute(key.ToString(), string.Join(" ", this.attrValues[key].ToArray()));

        this.attrValues = new Dictionary<HtmlTextWriterAttribute, List<string>>();
    }
}