asp.netvb.nethtmlgenericcontrol

HtmlGenericControl("br") rendering twice


I'm adding some content to a given web page from code behind. When I want to add a break after some text, I try to do that this way:

pDoc.Controls.Add(New Label With {.Text = "whatever"})
pDoc.Controls.Add(New HtmlGenericControl("br"))

,where pDoc is the Panel in which I'm adding the content. But it adds two br tags into the final HTML.

I've avoid this behaviour this way:

pDoc.Controls.Add(New Label With {.Text = "whatever" & "<br />"})

Anyway, I'm so curious and I want to know why

pDoc.Controls.Add(New HtmlGenericControl("br"))

is acting that way. I also think my approach is not too fancy.

Regards,


Solution

  • After some testing it looks like the reason is that HtmlGenericControl doesn't support self closing. On server side the HtmlGenericControl("br") is treated as:

    <br runat="server"></br>
    

    There is no </br> tag in HTML, so the browser shows it as there are two <br /> tags. Nice way out of this is to create HtmlGenericSelfCloseControl like this (sorry for C# code but you should have no issue with rewritting this in VB.NET):

    public class HtmlGenericSelfCloseControl : HtmlGenericControl
    {
        public HtmlGenericSelfCloseControl()
            : base()
        {
        }
    
        public HtmlGenericSelfCloseControl(string tag)
            : base(tag)
        {
        }
    
        protected override void Render(HtmlTextWriter writer)
        {
            writer.Write(HtmlTextWriter.TagLeftChar + this.TagName);
            Attributes.Render(writer);
            writer.Write(HtmlTextWriter.SelfClosingTagEnd);
        }
    
        public override ControlCollection Controls
        {
            get { throw new Exception("Self closing tag can't have child controls"); }
        }
    
        public override string InnerHtml
        {
            get { return String.Empty; }
            set { throw new Exception("Self closing tag can't have inner content"); }
        }
    
        public override string InnerText
        {
            get { return String.Empty; }
            set { throw new Exception("Self closing tag can't have inner text"); }
        }
    }
    

    And use it instead:

    pDoc.Controls.Add(New Label With {.Text = "whatever"})
    pDoc.Controls.Add(New HtmlGenericSelfCloseControl("br"))
    

    As a simpler alternative (if you have reference to the Page) you can try using Page.ParseControl:

    pDoc.Controls.Add(New Label With {.Text = "whatever"})
    pDoc.Controls.Add(Page.ParseControl("br"))