$User.UITheme not working on viualforce page

Question

I'm trying to detect on a visualforce page that is the page opened in a classic or Lightning view in Salesforce. For this I'm using "$User.UITheme" and "$User.UIThemeDisplayed" on the visualforce page and it is always return "Theme3". Also, when I use the UserInfo.getUiThemeDisplayed() method in the controller and display on the page it shows "Theme3" instead of "Theme4d" even if I'm in the lightning experience.

Here is the controller code:-

public with sharing class CheckUITheme {

    public String themeViewed{get;set;}

    public CheckUITheme(){
        themeViewed = UserInfo.getUiThemeDisplayed();
        System.debug('>>>>>'+UserInfo.getUiThemeDisplayed());
    }
}

Here is the Visualforce page code:-

 <apex:page controller="CheckUITheme"> 
  <h1>Congratulations</h1> This is your new Page
>>>>>>>>{!themeDisplayed}>>>>>>>>>
>>>>>>>>{!themeViewed}>>>>>>>>> {!$User.UITheme} {!$User.UIThemeDisplayed}  
</apex:page>

and the output which I get is :-

Congratulations This is your new Page >>>>>>>Theme3>>>>>>>>> >>>>>>>Theme3>>>>>>>>> Theme3 Theme3

What wrong m I doing here or is there a bug in the Salesforce method?

Answer 1

"{!$User.UITheme} {!$User.UIThemeDisplayed}", worked for me on the visualforce page when I used it in a inline visualforce page with the Standard controller and when I previwed the page as a visualforce page only it does not work. Strange but, the theme detection works for standard controllers on a inline VF page.