JPanel更改颜色以使用鼠标绘制

Question

I am trying to use JPanel to paint on the canvas using the mouse. So far everything works fine. I can draw. and I can set the color to be whatever I choose. However I am trying to make it so that when I click a button, it changes the color to whatever the button is attached to.

Like if I draw with black, then hit the "Blue" button, it changes to blue instead of black...I'm not sure on where I'm going wrong though. Heres my paintComponent part.

@Override
public void paintComponent(Graphics g)
{
    super.paintComponent(g);

    button1.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (e.getSource() == button1)
                g.setColor(Color.BLUE);
        }
    });

    for (Point point : points)
        g.fillOval(point.x, point.y, 4 , 4);
}

Answer 1

No, no, no. Why are you adding a ActionListener to a button inside a paint method? The paint method could be called a dozen times in quick succession by the repaint manager, now you have a dozen or more ActionListener s registered to the button .. which aren't going to do anything.

Start by creating a field which can store the desired paint color. Register a ActionListener to your buttons, probably via the classes constructor, which change the "paint color" and trigger a new paint cycle. When paintComponent called, apply the desired paint color

private Color paintColor = Color.BLACK;

protected void setupActionListener() {
    button1.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (e.getSource() == button1) {
                paintColor = Color.BLUE;
                repaint();
            }
        }
    });    
}

@Override
public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    g.setColor(paintColor);
    for (Point point : points)
        g.fillOval(point.x, point.y, 4 , 4);


}

Now, go and read Performing Custom Painting and Painting in AWT and Swing to gain a better understand into how painting actually works in Swing