C# - Reference An ASP Control Inside A Function Or Class Method?

How do you reference an asp.net control on your page inside a function or a class.
private void PageLoad(object sender, EventArgs e)
{
//An example control from my page is txtUserName
ChangeText(ref txtUserName, "Hello World");
}
private void ChangeText(ref HtmlGenericControl control, string text)
{
control.InnerText = text;
}
Will this actually change the text of the txtUserName control?
I tried this and is working
private void PageLoad(object sender, EventArgs e)
{
ChangeText(txtUserName, "Hello World");
}
private void ChangeText(TextBox control, string text)
{
control.Text = text;
}