FakeFile.cs

public partial class MyWebPage {
  public void SomeMethod() {
    var imaginaryValues = /* Some long string array of values */
    Page.GetWebValueControls().ForEach(c => {
      c._getOrSetControlValue(true, imaginaryValues[THE_CORRECT_INDEX]);
    });
  }
}

public static class Extensions {
  public static IEnumerable<Control> GetWebValueControls(this Control control) {
      return (from n in control.Controls.Cast<Control>().Descendants(c => c.Controls.Cast<Control>())
              where (n as TextBox != null
              || n as HtmlInputText != null
              || n as HtmlInputHidden != null
              || n as HtmlInputCheckBox != null
              || n as HtmlInputRadioButton != null
              || n as CheckBox != null
              || n as CheckBoxList != null
              || n as RadioButton != null
              || n as RadioButtonList != null
              || n as DropDownList != null
              || n as HtmlSelect != null
              || n as HtmlTextArea != null
              || n as Calendar != null)
              select n);
  }
  
  public static IEnumerable<T> Descendants<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> DescendBy) {
      foreach (T value in source) {
          yield return value;
  
          foreach (T child in DescendBy(value).Descendants<T>(DescendBy)) {
              yield return child;
          }
      }
  }
          
  private static string _getOrSetControlValue(this Control control, bool set = false, string val = "") {
      var ctrltype = control
          .GetType()
          .ToString()
          .ToLower()
          .Replace("system.web.ui.", "")
          .Replace("htmlcontrols.", "")
          .Replace("webcontrols.", "");
      var value = "";
      switch (ctrltype) {
          case "textbox":
              if (set) ((TextBox)control).Text = val;
              value = ((TextBox)control).Text;
              break;
          case "htmlinputtext":
              if (set) ((HtmlInputText)control).Value = val;
              value = ((HtmlInputText)control).Value;
              break;
          case "htmlinputhidden":
              if (set) ((HtmlInputHidden)control).Value = val;
              value = ((HtmlInputHidden)control).Value;
              break;
          case "htmltextarea":
              if (set) ((HtmlTextArea)control).Value = val;
              value = ((HtmlTextArea)control).Value;
              break;
          case "htmlinputcheckbox":
              if (set) ((HtmlInputCheckBox)control).Checked = bool.Parse(val);
              value = ((HtmlInputCheckBox)control).Checked.ToString();
              break;
          case "htmlinputradiobutton":
              if (set) ((HtmlInputRadioButton)control).Checked = bool.Parse(val);
              value = ((HtmlInputRadioButton)control).Checked.ToString();
              break;
          case "checkbox":
              if (set) ((CheckBox)control).Checked = bool.Parse(val);
              value = ((CheckBox)control).Checked.ToString();
              break;
          case "radiobutton":
              if (set) ((RadioButton)control).Checked = bool.Parse(val);
              value = ((RadioButton)control).Checked.ToString();
              break;
          case "checkboxlist":
              if (set) ((CheckBoxList)control).SelectedValue = val;
              value = ((CheckBoxList)control).SelectedValue;
              break;
          case "radiobuttonlist":
              if (set) ((RadioButtonList)control).SelectedValue = val;
              value = ((RadioButtonList)control).SelectedValue;
              break;
          case "dropdownlist":
              if (set) ((DropDownList)control).SelectedValue = val;
              value = ((DropDownList)control).SelectedValue;
              break;
          case "htmlselect":
              if (set) ((HtmlSelect)control).Value = val;
              value = ((HtmlSelect)control).Value;
              break;
          case "calendar":
              if (set && val._decodeString() != "1/1/0001") ((Calendar)control).SelectedDate = DateTime.Parse(val);
              value = ((Calendar)control).SelectedDate.ToShortDateString();
              break;
          default:
              value = "";
              break;
      }
  
      return value;
  }
}