How do I make my custom bitmap button field use a transparent background?

Question

I have a custom bitmap buttonfield that completely works, however, the background behind the image is showing a white rectangle. I've found where it makes the color white, but I cannot figure out how to make it completely transparent. Any ideas? I'm programming in blackberry java JDE 5.0

FYI The button image is a rounded corner png file that uses transparency on the corners

Code:

public class BitmapButtonField extends Field 
{

    Bitmap _currentPicture;
    private Bitmap _onPicture;
    Bitmap _offPicture;
    private int id;


    public BitmapButtonField (Bitmap  onImage, Bitmap offImage)
    {
       super(Field.FOCUSABLE|Field.FIELD_HCENTER);
       _offPicture = offImage;
       _onPicture = onImage;
       _currentPicture = _onPicture;
    }

    public void setButtonImage (Bitmap onImage, Bitmap offImage)
    {
        _offPicture = offImage;
        _onPicture = onImage;
        _currentPicture = _onPicture;
     }

    public void setButtonId(int id)
    {
        this.id = id;
    }
    public int getButtonId()
    {
        return this.id;
    }    

    public int getPreferredHeight()
    {
        return _onPicture.getHeight();
    }


    public int getPreferredWidth()
    {
        return _onPicture.getWidth();
    }

    protected void onFocus(int direction)
    {
        _currentPicture = _offPicture;
       invalidate();
    }

    protected void onUnfocus()
    {
        _currentPicture = _onPicture;
       invalidate();
    }

    protected void drawFocus(Graphics g, boolean on)
    {        
        g.setBackgroundColor(Color.BLACK);
    }

    protected void layout(int width, int height) 
    {
        setExtent(Math.min( width, getPreferredWidth()), Math.min( 
                            height, getPreferredHeight()));
    }

    protected void paintBackground(Graphics g) {
          int prevColor = g.getColor();
          int prevAlpha = g.getGlobalAlpha();
          g.setColor(Color.YELLOW);
          g.setGlobalAlpha(0);
          g.fillRect(0, 0, getWidth(), getHeight()); // or g.getClippingRect()
          g.setColor(prevColor);
          g.setGlobalAlpha(prevAlpha);
        }

        protected void paint (Graphics graph){

        graph.setColor(Color.WHITE);
        //super.paint(graph);

        graph.fillRect(0, 0, getWidth(), getHeight());
        graph.drawBitmap(0, 0, getWidth(), getHeight(), 
                             _currentPicture, 0, 0);    
        }


    protected boolean navigationClick(int status, int time)
    {
        fieldChangeNotify(0);
        return true;
    }

    public boolean keyChar(char key, int status, int time)
    {
        if (key == Characters.ENTER)
        {
            fieldChangeNotify(0);
            return true;
        }
        return false;
    }
}

Answer 1

You have implemented

protected void drawFocus(Graphics g, boolean on)

and

protected void paintBackground(Graphics g)

And you have also specified the background image for focused state. You can remove the implementation of paintBackground() and drawFocus(). Also the line which set the graphics color to white and fills a rectangle can be deleted from the method paint. That is you need to only paint the bitmap image on the paint method. I have modified your code here, You can check that (I didn't test it).