从另一个JPanel内部重新绘制一个JPanel

Question

So, I am making a painting program and I have a main Paint class which detects mouse input and paints and a Tools class which is a toolbar on the left which holds a bunch of tools, like brush size change and shape change. So, I want to add a clear button to the Tools class which clears the whole screen. My problem is that the Paint class is holding the ArrayList of points which it paints and I can't repaint Paint from within Tools .

Paint class

//imports    
public class Paint extends JPanel{
    private ArrayList<Brush> points;
    ...

    public Paint() {
        ...
    }

    public void paintComponent(Graphics page) {
        ...

        //draws all points in the arraylist
        for (Brush b : points) {
            //paint points
        }
    }
}

Tools class

//imports
public class Tools extends JPanel
{
    private JButton clear;

    public Tools() {
        clear = new JButton("Clear");
        clear.addActionListener(new BrushInput());
    }

    public void paintComponent(Graphics page) {
        ...
    }
    private class BrushInput implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            if (e.getSource() == clear) {
                //clear points arraylist and repaint
            }
        }
    }

}

The issue I'm having is that repaint() is an instance method and so I can't access Paint 's repaint from within Tools .

Answer 1

Just pass a reference to the Paint instance to Tools 's constructor. Or, call repaint on the container ( JFrame , etc.) that contains both of them, which should cause all its children to be repainted.

For example:

public class Paint extends JPanel {
    private ArrayList<Brush> points;

    // . . .

    public void clear() {
        points.clear();
        repaint();
    }
}

public class Tools extends JPanel {
    private JButton clear;
    private Paint paint;

    public Tools(Paint paint) {
        this.paint = paint;
        // . . .
    }

    // . . .

    private class BrushInput implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            if (e.getSource() == clear) {
                paint.clear();
            }
        }
    }
}

Code that creates these components:

Paint paint = new Paint();
Tools tools = new Tools(paint);