It seems that you are using the custom form created from SharePoint list. If so, may I know why you want to have 3 screens just for different display mode of Form control? Because by default, the custom form should have one form, and it will change its mode to View/Edit/New according to what user select on SharePoint list interface.
Why I need 3 screens is I just want to open attached file in online. But I think onselect action can use in editable form and action:editform(formname) or viewer form and action viewform(formname). that's why I need 3 screens.
If it can open attached file in online on view mode, that's fine.