RecyclingImageView

/**
 * Sub-class of ImageView which automatically notifies the drawable when it is
 * being displayed.
 */
public class RecyclingImageView extends ImageView {

	public RecyclingImageView(Context context) {
		super(context);
	}

	public RecyclingImageView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	public RecyclingImageView(Context context, AttributeSet attrs,
			int defStyleAttr) {
		super(context, attrs, defStyleAttr);
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see android.widget.ImageView#onDetachedFromWindow()
	 */
	@Override
	protected void onDetachedFromWindow() {
		// This has been detached from Window, so clear the drawable
		setImageDrawable(null);

		super.onDetachedFromWindow();
	}

	/**
	 * @see android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)
	 */
	@Override
	public void setImageDrawable(Drawable drawable) {
		// Keep hold of previous Drawable
		final Drawable previousDrawable = getDrawable();

		// Call super to set new Drawable
		super.setImageDrawable(drawable);

		// Notify new Drawable that it is being displayed
		notifyDrawable(drawable, true);

		// Notify old Drawable so it is no longer being displayed
		notifyDrawable(previousDrawable, false);
	}

	/**
	 * Notifies the drawable that it's displayed state has changed.
	 *
	 * @param drawable
	 * @param isDisplayed
	 */
	private static void notifyDrawable(Drawable drawable,
			final boolean isDisplayed) {
		if (drawable instanceof RecyclingBitmapDrawable) {
			// The drawable is a CountingBitmapDrawable, so notify it
			((RecyclingBitmapDrawable) drawable).setIsDisplayed(isDisplayed);
		} else if (drawable instanceof LayerDrawable) {
			// The drawable is a LayerDrawable, so recurse on each layer
			LayerDrawable layerDrawable = (LayerDrawable) drawable;
			for (int i = 0, z = layerDrawable.getNumberOfLayers(); i < z; i++) {
				notifyDrawable(layerDrawable.getDrawable(i), isDisplayed);
			}
		}
	}

}