A runable that handles only transitioning and crossfading when the bitmaps are different.

TransitionDrawableRunnable.java

import android.content.SharedPreferences;
import android.graphics.Bitmap;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.TransitionDrawable;
import android.preference.PreferenceManager;
import android.view.View;

/**
 * A runnable that transitions between a drawable and a bitmap.
 * 
 * It supports not doing transitions when the bitmaps are the same.
 * 
 * It currently depends on setting transitions at all if there is a 
 * fade in transition preference enabled in the app.   Remove that
 * section of code if you don't need this support.
 * 
 * If transition support isn't enabled then it doesn't do transitions
 * and just sets the bitmap as the background to the view passed in
 * the constructor.
 * 
 * Code licensed under an MIT license so do what you want just give
 * attribution where it was obtained.
 * 
 * 
 * @author davidcarver
 *
 */

public class BackgroundBitmapDisplayer implements Runnable {

	protected Bitmap bitmap;
	protected int defaultImageId;
	protected View backgroundView;

	public BackgroundBitmapDisplayer(Bitmap bitmap, int defaultImage, View view) {
		this.bitmap = bitmap;
		this.defaultImageId = defaultImage;
		this.backgroundView = view;
	}

	@Override
	public void run() {
		if (bitmap == null) {
			backgroundView.setBackgroundResource(defaultImageId);
			return;
		}

		SharedPreferences preferences = PreferenceManager
				.getDefaultSharedPreferences(backgroundView.getContext());
		boolean shouldFadeIn = preferences.getBoolean(
				"animation_background_fadein", false);

		BitmapDrawable bitmapdrawable = new BitmapDrawable(backgroundView
				.getContext().getResources(), bitmap);

		if (!shouldFadeIn) {
			backgroundView.setBackgroundDrawable(bitmapdrawable);
			return;
		}

		crossfadeImages(bitmapdrawable);
	}

	private void crossfadeImages(BitmapDrawable newBitmapDrawable) {
		Drawable currentDrawable = backgroundView.getBackground();
		if (currentDrawable instanceof TransitionDrawable) {
			currentDrawable = ((TransitionDrawable) currentDrawable)
					.getDrawable(1);
		}

		if (currentDrawable == null) {
			currentDrawable = backgroundView.getContext().getResources()
					.getDrawable(defaultImageId);
		}

		Drawable[] drawables = { currentDrawable, newBitmapDrawable };
		TransitionDrawable transitionDrawable = new TransitionDrawable(
				drawables);
		backgroundView.setBackgroundDrawable(transitionDrawable);
		transitionDrawable.setCrossFadeEnabled(true);
		int crossfadeduration = 200;
		if (currentDrawable instanceof BitmapDrawable) {
			BitmapDrawable currentBitmapDrawable = (BitmapDrawable) currentDrawable;
			if (currentBitmapDrawable.getBitmap().sameAs(
					newBitmapDrawable.getBitmap())) {
				transitionDrawable.setCrossFadeEnabled(false);
				crossfadeduration = 0;
			}
		}
		transitionDrawable.startTransition(crossfadeduration);
	}
}