c# - error using FindControl on div id

Question

I have an ASP.NET site that I am trying to access div elements by their ID from the C# code behind file. Essentially I want to see if a div element exists, and if so, alter its

Answer 1

If your page is using a MasterPage, the div control will not be in the main collection of controls. That collection only contains the Content controls pointing to the ContentPlaceholder of your MasterPage.

There are three options:

1. Use FindControl on the Content control: contentControl.FindControl("button1");
2. Do a recursive FindControl until you find the control you need
3. Normally, a declaration of your div control is added to your designer.cs codebehind, so you can directly access the control by its name: button1.Attributes["class"] = "classNameHere";

Update

I have created a MasterPage, added a Content Page to it, and added

Some text

to the Content Page.

In the codebehind of my Content Page, I added this code:

protected void Page_Load(object sender, EventArgs e)
{
    var control = FindHtmlControlByIdInControl(this, "button1");

    if (control != null)
    {
        control.Attributes["class"] = "someCssClass";
    }
}

private HtmlControl FindHtmlControlByIdInControl(Control control, string id)
{
    foreach (Control childControl in control.Controls)
    {
        if (childControl.ID != null && childControl.ID.Equals(id, StringComparison.OrdinalIgnoreCase) && childControl is HtmlControl)
        {
            return (HtmlControl)childControl;
        }

        if (childControl.HasControls())
        {
            HtmlControl result = FindHtmlControlByIdInControl(childControl, id);
            if (result != null) return result;
        }
    }

    return null;
}

This works for me.