Image is not being painted upon dragging mouse

Question

I am making some project which requires dragging objects on the screen. In my main class I have such listener

addMouseMotionListener(new MouseMotionAdapter(){
            public void mouseDragged(MouseEvent e){
                currentX = e.getX() - 10 ;
                currentY = e.getY() - 5;

                if(currentNote != null)
                {

                    if(!editingMode)
                    {
                        graphics2D.setPaint(Color.BLACK);
                        currentNote.setParameters(currentX, currentY, NoteDrawing.SKIP_CHECK);
                        currentNote.paintComponent(graphics2D);

                    }
                    else
                    {
                        graphics2D.setPaint(Color.BLACK);
                        currentNote.setParameters(currentNote.getBallFromX(), currentY, NoteDrawing.SKIP_CHECK);
                        currentNote.paintComponent(graphics2D);
                    }

                }
                repaint();
            }
        })

Now in the object (extending JComponent) which should be painted I have the following paintComponent method:

public void paintComponent(Graphics g) {
        g.drawImage(bmoll,fromX, fromY,null);
        g.drawLine(fromX, fromY, fromX + 30, fromY);
        repaint();

    }

and the setting parameters method:

public void setParameters(int x, int y) {
        this.fromX = x;
        this.fromY = y;

    }

When I press the button over the object and then drag the mouse, the line drawn in paintComponent method is dragged properly, the image however is not. The image is not null - it appears on the screen in its original position. If I duplicate the line g.drawImage(bmoll,fromX, fromY,null); with different coordinates it is being drawn in two places as it should. But when I drag the mouse - nothing happens with it. If anyone has some suggestions about what is causing the problem, I shall be grateful.

1) For better help sooner, post an [MCVE](http://stackoverflow.com/help/mcve) (Minimal Complete and Verifiable Example). 2) One way to get image(s) for an example is to hot-link to the images seen in [this answer](http://stackoverflow.com/a/19209651/418556). 3) You forgot to ask a question. What is your question? — Andrew Thompson, May 14 '14 at 10:23
My question... I meant to ask what causes my problem. Now it is not relevant anymore, cause thanks to your suggestion about MCVE I found what the bug was while I was preparing the example to post. The problem was in one of the objects constructor. Thank you for your help!! — user3107531, May 14 '14 at 12:05
I choose to write an answer just in case anyone got similar problem - I'll be able to accept it in two days though. — user3107531, May 14 '14 at 12:20
*"I choose to write an answer just in case anyone got similar problem"* I was hoping you'd choose that option. ;) — Andrew Thompson, May 14 '14 at 13:21

score 1 · Accepted Answer · answered May 14 '14 at 12:18

Apparently the problem was in the object's constructor. In the original object's creation the program calls for:

public Bmoll(int startX, int startY)
    {
        this.fromX = startX;
        this.fromY = startY;
        this.inverted = false;
        this.staff = Staff.getActiveStaff();
        this.bmoll = GuiHelper.getImage(B_MOLL_FILE);
    }

while, when creating the object for dragging, the empty constructor was called and thus the image object bmoll was null - there was nothing to be drawn.

score 0 · Answer 2 · answered May 14 '14 at 10:28

Make sure you call super.paintComponent
Painting is done within the context of the paint methods, you should never need to call paint or paintComponent yourself
Use paintComponent to paint the current state
When clicked, prepare the state and call repaint
When dragged, update the state and call repaint

Image is not being painted upon dragging mouse

2 Answers2