Question

I have a problem making an inner class that extends from JPanel to draw anything on it. I overrided the paintComponent method, and whatever I set to draw from here works fine, but using another method to draw does not work.

Here is my inner class code:

private class Plot extends JPanel {

    public Plot() {
        this.setBackground(Color.WHITE);
    }

    @Override
    public void paintComponent(Graphics graphic) {
        super.paintComponent(graphic);
        Graphics2D graphic2d = (Graphics2D) graphic;

        graphic2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);

        graphic2d.drawOval(0, 0, this.getWidth() - 1, this.getHeight() - 1);
    }

    public void drawTitle(final String title) {
        Graphics2D graphic2d = (Graphics2D) this.getGraphics();
        graphic2d.setColor(Color.red);
        graphic2d.drawString(title, 1, 10);
    }
}

Notice the drawTitle method. I just want a custom text to be shown. In my outer class which extends from a JFrame I create an instance of this inner class like this:

private Plot plot;

/** Creates new form GraphicsView */
public GraphicsView() {
    initComponents();
    plot = new Plot();
    this.add(plot, BorderLayout.CENTER);
}

public void drawTitle(final String title) {
    this.plot.drawTitle(title);
}

I even create a convenient method to call the inner class drawTitle method (with the same name). I do this because I want this JFrame outer class to be visible on button click, once it is visible (which ensures the init of the graphics) I call the outer class drawTitle which in turn calls the inner class method with the same name and where the string show be drawn… but this does not work, I can’t see it on the panel. Here is my button click event:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    GraphicsView view = new GraphicsView();
    view.setVisible(true);
    view.drawTitle("Hello");
}

Thanks in advance, I will appreciate any help. 🙂

Answer 1

I overrided the paintComponent method, and whatever I set to draw from here works fine

Well, there is the answer to the question. Do all your drawing from the paintComponent() method.

but using another method to draw does not work.

Don’t use the getGraphics() method. You should only ever use the Graphics objects passed to the paintComponent() method.

You can’t control when Swing repaints() a component. Therefore every time the component is repainted the paintComponent() method is invoked and your other custom painting code will be lost.