Rendering a server-side control using HTMLTextWriter makes control lose standard functionality (i.e. Click eventhandler)

Question

I want to add Server-Side controls (CheckBoxLists & Button):

ChkBoxLst1 & ChkBoxLst2 & Button1 through Code-behind and then use an HTMLTextWriter to render the control.

I can't seem to be able to do this.

All of the above in a Visual WebPart.

What I have tried:
Global:

CheckBoxList ChkBoxLst2 = new CheckBoxList();
Button Bttn2 = new Button();
Label lbl2 = new Label(); 

StringWriter stringWriter = new StringWriter();

Page Load:

using (HtmlTextWriter writer = new HtmlTextWriter(stringWriter))
        {
            ChkBoxLst2.Items.Add(new ListItem("Three", "3"));
            ChkBoxLst2.Items.Add(new ListItem("Four", "4"));

            ChkBoxLst2.RenderControl(writer);
            lbl2.RenderControl(writer);
            Bttn2.Click += new EventHandler(this.Bttn2_Click);
            Bttn2.Text = "Click this HTMLText WriteButton!";
            Bttn2.RenderControl(writer); 

        }

        spn.InnerHtml = stringWriter.ToString();

Event Handler:

 void Bttn2_Click(Object sender, EventArgs e)
    {
        foreach (ListItem item in ChkBoxLst2.Items)
        {
            if (item.Selected == true)
            {
                if (IsPostBack)
                {
                    lbl.Text += item.Text + ", ";
                }
            }
        }
    }

The EventHandler does not get triggered and the selected values do not get saved the way I have done it above. Any ideas as to why not? I've tried a comparison of two checkbox lists, but the HTMLTextWriter implementation did not work whereas the simple .NET did of the same thing
all in all I think its my implementation of an HTMLTextWriter/how I add the server control.

Note that the spn is a literal span control in the markup.

Can you show us what you tried, and what problem you had? – John Saunders Mar 02 '12 at 16:01 — John Saunders, Mar 02 '12 at 16:01
@JohnSaunders ok I'll edit the question – anpatel Mar 02 '12 at 18:38 — anpatel, Mar 02 '12 at 18:38

score 4 · Answer 1 · answered Mar 02 '12 at 15:49

4

try this method to render controls into an html string:

    public static string ControlRenderToString(Control tmpControl)
    {
        string Content;

        System.IO.StringWriter sWriter = new System.IO.StringWriter();
        HtmlTextWriter htwObject = new HtmlTextWriter(sWriter);
        tmpControl.RenderControl(htwObject);

        Content = sWriter.ToString();
        sWriter.Close();

        return Content;
    }

answered Mar 02 '12 at 15:49

Shlomi Komemi

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I think that is what I have, but I'm not sure maybe I'm overlooking something. I've edited the question with some code and detail. – anpatel Mar 02 '12 at 18:52
@MyName, i don't think you can use you're click handler after rendering the control, try using javascript / ajax instead. – Shlomi Komemi Mar 02 '12 at 19:34
I'm calling the Click handler before rendering the control though, or does it get executed in a different sequence? – anpatel Mar 02 '12 at 19:57

score 2 · Accepted Answer · answered Mar 02 '12 at 19:04

Although you have rendered these controls to the browser, the controls are not part of the control tree of the page, and will not even exist on postback. Any dynamically-added controls need to be added on every request.

Why play with HtmlTextWriter at all? Simply add the controls to the page during Page_Load, and they'll be rendered for you. Do so outside of the "if (!Page.IsPostBack)" and they'll be there every time the page loads, which is what you want.

thank you so much!! The behavior makes much much more sense now. — anpatel, Mar 02 '12 at 19:45

Rendering a server-side control using HTMLTextWriter makes control lose standard functionality (i.e. Click eventhandler)

2 Answers2