@samuelagus What happens if you set the default to one of the existing options, e.g. “1”?

@richard67 if I set the default to "1", it will automatically choose In Process, it's normal as expected

@samuelagus Well, I would assume that the default should be one of the available options.

oh... I see...
My questions are:

1. My old custom component still work normally in J3.9.23. Why in J3! it could use default="" or default="0" even though there is no "0" in the options value?
2. I design the radio options as a three big button: In Process Return Sent. So the user can choose the radio option by only (once) click the button easily. Would you give me the tips/tricks how to force the user to choose an (radio) option before the form can be saved or submitted?
   Thank you :)

1. You should not the setting a default in the xml - just delete that line (tested and works)
2. Be careful with the field name/id of status to ensure that it is unique on the form

@brianteeman Now I remove the default line from XML, then try to save the form without select the radio button. The form save successfully then automatically go to list page, then showing the error notification in top of list page: Field required: Status. All fields values saved successfully in DB except the radio field value because there is no radio value selected before.

In my expectation, the error notification should be shown above the radio field (like the list field I describe before), then prevent to save the form.

Then you have a problem elsewhere.

Screenshot of my test

I design the radio options as a three big button: In Process Return Sent. So the user can choose the radio option by only (once) click the button easily. Would you give me the tips/tricks how to force the user to choose an (radio) option before the form can be saved or submitted?

Not tested, but that should be possible by adding

layout="joomla.form.field.radio.buttons"

to your field and remove your own design.

A radio field is defined that it must have one of several alternatives. Otherwise it is a checkbox or checkboxes.
You cold add an option 0 = "waiting" to your list of options, and set "0" as default.

I thought that as well but I was wrong see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio

and anyway I have shown above that the users code does work correctly as they intend when used with a core component

Yes, this is possible - but from UX it looks like a bug (maybe only for me). I expect always an option like "none".

In the following link we see some examples with big buttons - they use checkboxes which seems a better solution and radio also with buttons. Both examples look good for me.
https://ux.stackexchange.com/questions/76181/radio-buttons-with-none-selected

the reason to use radio groups is so that you can only check 1/3 options. checkboxes dont restrict you in that way

@samuelagus Well, I would assume that the default should be one of the available options.

A radio field is defined that it must have one of several alternatives. Otherwise it is a checkbox or checkboxes. You cold add an option 0 = "waiting" to your list of options, and set "0" as default.

@richard67 @chmst If I add an option "0" then set "0" as default, when the user forget to choose the "status" field ( "1" | "2" | "3"), then the status field will be save as "0". It's not what I want :)
I just want to force the user to choose one of the radio options, otherwise the form won't be saved.

How to force a "required" field or have a validation, so the status field cannot be "0" or "" (blank)?

I design the radio options as a three big button: In Process Return Sent. So the user can choose the radio option by only (once) click the button easily. Would you give me the tips/tricks how to force the user to choose an (radio) option before the form can be saved or submitted?

Not tested, but that should be possible by adding

layout="joomla.form.field.radio.buttons"

to your field and remove your own design.

@ReLater I've remove the css so now it looks like plain radio options, then add layout="joomla.form.field.radio.buttons" still get the same result: the form saved without "status" radio field chosen, even though I have add required="true" in the XML form

I thought that as well but I was wrong see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio

and anyway I have shown above that the users code does work correctly as they intend when used with a core component

@brianteeman I'm confused, what's wrong with my codes. It worked normally in J3! until now I'm still using it in J3!

@samuelagus

@ReLater I've remove the css so now it looks like plain radio options, then add layout="joomla.form.field.radio.buttons" still get the same result: the form saved without "status" radio field chosen, even though I have add required="true" in the XML form

Yes, you're right. I relied on the PHP code of that JLayout. Later I tried a lot of variations with 3 buttons and never had a CLIENT-SIDE(!!!) validation that told me that the field is required. Only after save & page reload a message like in your opening comment (SERVER-SIDE validation). But I was very tired and didn't check if something was saved in DB.

PR #39578 should address this issue. Please help testing. Thanks !

PR #39578 should address this issue. Please help testing. Thanks !

I have tested #39578

The result as expected, there is an error message above the radio field: One of the options must be selected when no radio option selected :)

@samuelagus That mean the PR solves your issue? If so, please go to https://issues.joomla.org/tracker/joomla-cms/39578 , click on Test this to report your test result as Success so that the PR could be merged.