====== Eclipse e4 RCP Theming ======

Giving an Eclipse e4 application a new theme is rather easy with the e4 css theme support. There are many tutorials and articles about it.

And you can give your e4 RCP application a distinct theme. No problem there. But when you want to give your user the ability to switch themes that is a completely other story. Switching themes includes accessing the ''IThemeManager'' which is in the package ''org.eclipse.ui.themes''. Still sounds easy enough. Importing the package as a dependency and add the bundle ''org.eclipse.ui.themes'' to the application build and we are all done.

<note warning>Problem with this is that ''org.eclipse.ui.themes'' seems to depend on parts of the Eclipse IDE which you normally don't have in an Eclipse e4 RCP application. So this approach does not work.</note>

There is a bundle with the symbolic name ''org.eclipse.ui.themes'' but it doesn't export the java package ''org.eclipse.ui.themes''. The bundles contains the CSS and image files but no java package.

I found the package in the bundle ''org.eclipse.ui.workbench''. What the f...!!! That is an Eclipse 3.x bundle. 

So no ''IThemeManager'' for switching themes.

But if we can't switch themes dynamically perhaps we can load the correct theme on application start ... and yes, that is possible. Long live the ''PartRenderingEngine''.

<sxh java>
import org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine;
import org.eclipse.e4.core.contexts.IEclipseContext;
import org.eclipse.e4.ui.workbench.lifecycle.PostContextCreate;

public class LifeCycleManager {

	@PostContextCreate
	void postContextCreate(IEclipseContext context) {
		String cssURI = "platform:/plugin/miworkplace.ui.themes/css/dark.css";
		this.context.set(E4Workbench.CSS_URI_ARG, cssURI);
		PartRenderingEngine.initializeStyling(Display.getCurrent(), this.context);
	}
}
</sxh>

====== Update ======

This also works for setting/switching a theme.

The necessary classes can be found in the plugin ''org.eclipse.e4.ui.css.swt.theme''.

<sxh java>
@Inject
private IThemeManager themeManager;

IThemeEngine engine = themeManager.getEngineForDisplay(Display.getCurrent());
for (ITheme theme : engine.getThemes()) {
    if (theme.getId().equals(currentThemeId)) {
	engine.setTheme(theme, true);
	break;
    }
}
</sxh>

{{tag>devel java e4}}