e(fx)clipse 1.2.0 is trying to get a better OSGi citizen and so we try to remove more and more Equinox/Eclipse specific stuff which means that we want to get rid of the Extension Registry in our/your code.

In 1.1.0 themes have been defined using the theme extension point org.eclipse.fx.ui.theme where you’ve been able to:

• Define a theme
• Contribute Stylesheets to themes

In 1.2.0 we deprecated the extension point in favor of making Themes and Stylesheets OSGi-Services you e.g. contribute through declarative services.

There are 2 main advantages:

• We get dynamics for free so themes and stylesheets can be installed/updated/uninstalled in a running application
• You have much more control over contributing a Stylesheet e.g. whether it applies to a given theme

A disadvantage if you want to find one is that it is a bit more work to define the theme and looks like this

<?xml version="1.0" encoding"UTF-8"?>
<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" name="org.eclipse.fx.code.compensator.app.default-theme">
  <implementation 
    class="org.eclipse.fx.code.compensator.app.DefaultTheme"/>
   <service>
      <provide 
       interface="org.eclipse.fx.ui.services.theme.Theme"/>
   </service>
   <reference 
     bind="registerStylesheet" 
     cardinality="0..n" 
     interface="org.eclipse.fx.ui.services.theme.Stylesheet" 
     name="Stylesheet" 
     policy="dynamic" unbind="unregisterStylesheet"/>
</scr:component>

package org.eclipse.fx.code.compensator.app;

import org.eclipse.fx.ui.services.theme.Theme;
import org.eclipse.fx.ui.theme.AbstractTheme;
import org.osgi.service.component.annotations.Component;

public class DefaultTheme extends AbstractTheme {
  public DefaultTheme() {
    super("default", "Default Theme", 
      DefaultTheme.class.getClassLoader().getResource("css/default.css"));
  }
}