GwtPreloaderInterface.java

package com.example.preloader.client;

import com.badlogic.gdx.backends.gwt.GwtApplication;
import com.badlogic.gdx.backends.gwt.preloader.Preloader.PreloaderCallback;
import com.badlogic.gdx.backends.gwt.preloader.Preloader.PreloaderState;
import com.example.preloader.PreloaderInterface;

/**An implementatation of PreloaderInterface which forwards the request to
 * the GwtApplication's preloader. */
public class GwtPreloaderInterface implements PreloaderInterface {

  GwtApplication application;
  
	public GwtPreloaderInterface(GwtApplication application) {
		this.application = application;
	}
	
	@Override
	public void preloadBundle (final String bundle, final Callback callback) {
		application.getPreloader().preload(bundle + ".txt", new PreloaderCallback() {
			@Override
			public void update (PreloaderState state) {
				if (state.hasEnded()) {
					callback.onBundlePreloaded(bundle);
				}
			}
			@Override
			public void error (String file) {
			}
		});
	}

}

NullPreloaderInterface.java

package com.example.preloader;

/**An implementatation of PreloaderInterface which returns immediately. This
 * implementation should be used where a Preloader is not required. */
public class NullPreloaderInterface implements PreloaderInterface {
  
	@Override
	public void preloadBundle (final String bundle, final Callback callback) {
		callback.onBundlePreloaded(bundle);
	}

}

PreloaderInterface.java

package com.example.preloader;

/** Provides a way to interact with the preloader, if one exists. */
public interface PreloaderInterface {

  /**Request that the named bundle be preloaded.
	 * 
	 * @param bundle the name of the bundle
	 * @param callback to be called upon preload completion
	 */
	public void preloadBundle(String bundle, Callback callback);

	/** Allows the PreloaderInterface to communicate back to the caller. */
	public interface Callback {

		/**Called when the named bundle has been preloaded.
		 * 
		 * @param bundle the name of the bundle
		 */
		void onBundlePreloaded(String bundle);

	}
}