adding method to class file

1. Make sure the class is public

2. Make sure both class and ASP.Net page belong to same namespace otherwise you need to inherit namespace

If the above is correct paste your class file code using "Add Code" button

 public void disableFormcontrols(Control parent)// 
        {
            foreach (Control c in parent.Controls)
            {
                if (c.Controls.Count > 0)
                {
                    disableFormcontrols(c);
                }
                else
                {
                    switch (c.GetType().ToString())
                    {
                        case "System.Web.UI.WebControls.Text.Trim()Box":
                            ((TextBox)c).ReadOnly = true;
                            break;
                        case "System.Web.UI.WebControls.CheckBox":
                            ((CheckBox)c).Enabled = false;
                            break;
                        case "System.Web.UI.WebControls.RadioButton":
                            ((RadioButton)c).Enabled = false;
                            break;
                        case "System.Web.UI.WebControls.DropDownList":
                            ((DropDownList)c).Enabled = false;
                            break;

                        case "System.Web.UI.WebControls.Button":
                            cmdsave.Enabled  = false;
                            break;


                    }
                }
            }
        }

i tried using the same in my .aspx file using private instead of public

but there is no change in text controls

except the button control which gets disabled

i have the namespace

Your question is not clear.

1. You said you cannot call the method from class

Now you say that you are not able to enable/disable control.

Please clarify your exact problem

1) currently i have the above  code  in my .aspx file as i was not able to get it from class file

when used from aspx file as per the logic i need all the stated controls in the code to be readonly or disabled

i have call this method in page load

but still all the text controls are not readonly

2) as i need to use in in many places want to use it from class file

but i am bale to do it

hope its clear

Since you asked for the Class question here I'll answer to that here for for Enable/Disable logic you ask new question

As said before have you created an object of that class because first you need to create object and then you can call it