I'm trying to set a textfield readonly.

I see in the documentation that I can set a TextField to readonly, however how is this implemented?

I have a custom form, but where do I put the readonly part for the field I want to make readonly?

function Form() {
      return new Form($this, "Form", new FieldSet(

         // List your fields here
         new EmailField("Email", "Email address"),
         new PasswordField("Password", "Password"),
         new TextField("FirstName", "First name"),
         new TextField("LastName", "Last name"),
         new TextField("Phone", "Phone"),
         new TextField("Company", "Company/Hospital"),
         new TextField("Address1", "Address 1"),
         new TextField("Address2", "Address 2"),
         new TextField("City", "City"),
         new TextField("State", "State"),
         new TextField("Zip", "Zip"),
         new TextField("Country", "Country"),
         new TextField("IPAdress","IPAddress",$_SERVER['REMOTE_ADDR'])
         

      ), new FieldSet(

         // List the action buttons here
         new FormAction("SignupAction", "Register")

      ), new RequiredFields(

         // List the required fields here: "Email", "FirstName"
         "Email", "Password", "FirstName", "LastName", "Phone", "Company", "Address1", "City", "State", "Zip", "Country"

      ));
   }

Meh,

ReadonlyField

Did you try making it a readOnlyField rather than use my code above?