android gallery view “stutters” with deferred image loading adapter

Question

I would like to create an deferred loading adapter for use with a Gallery widget.

That is to say getView() returns an ImageView

Answer 1

I have an answer for you!

When any of the setImage... methods are called on ImageView in internally a layout pass is requested, for example, setImageBitmap() as above is defined as such

public void setImageBitmap(Bitmap bm) {
    setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}

which calls

public void setImageDrawable(Drawable drawable) {
    if (mDrawable != drawable) {
        mResource = 0;
        mUri = null;
        updateDrawable(drawable);
        requestLayout(); //layout requested here!
        invalidate();
    }
}

which has the effect of the gallery 'snapping' to the center of the image thats currently closest to the center of the gallery.

What I have done to prevent this is have the View thats loading into the Gallery have a explicit height and width (in dips) and using an ImageView subclass that ignores layout requests. This works as the gallery still has a layout pass initially but does not bother doing this every time an image in the gallery changes, which I imagine would only need to happen if the gallery views had their width and height set to WRAP_CONTENT, which we dont. Note that as invalidate() is still called in setImageDrawable() the image will still be drawn when set.

My very simple ImageView subclass below!

/**
 * This class is useful when loading images (say via a url or file cache) into
 * ImageView that are contained in dynamic views (Gallerys and ListViews for
 * example) The width and height should be set explicitly instead of using
 * wrap_content as any wrapping of content will not be triggered by the image
 * drawable or bitmap being set (which is normal behaviour for an ImageView)
 * 
 */
public class ImageViewNoLayoutRefresh extends ImageView
{
    public ImageViewNoLayoutRefresh(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
    }

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

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

    @Override
    public void requestLayout()
    {
        // do nothing - for this to work well this image view should have its dims
        // set explicitly
    }
}

edit: i should mention that the onItemSelected approaches can also work, but as I needed to hook into that while flinging was taking place I came up with the above, which I think is more flexible approach