Window's content disappears when minimized
awt, graphics, java, paint, swing
Solution
You are not storing the state of the points you are drawing. When the panel is repainted, it only has information for the last point it drew.
Response to comment:
You would need to have a collection of Points, for instance `ArrayList<Point> location = new ArrayList<Point>();`
Then, in your listeners: `location.add(new Point(me.getX(), me.getY()));`
Finally, in paintLine():
for (Point location : locations) {
repaint(location.x,location.y,1,1);
}
The collection `locations` is usually referred to as a Display List. Most graphics programs use them.
Response to comment:
Yes, I expect so. I just tossed off an idea based on your code to give you a starting point. It is almost certainly a bad idea to do exactly as I have described.
Problem
I have a simple class that draws a line when mouse dragging or a dot when mouse pressing(releasing). When I minimize the application and then restore it, the content of the window disappears except the last dot (pixel). I understand that the method `super.paint(g)` repaints the background every time the window changes, but the result seems to be the same whether I use it or not. The difference between the two of them is that when I don't use it there's more than a pixel painted on the window, but not all my painting. How can I fix this? Here is the class. ``` package painting; import java.awt.*; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.event.MouseMotionAdapter; import javax.swing.JFrame; import javax.swing.JPanel; class CustomCanvas extends Canvas{ Point oldLocation= new Point(10, 10); Point location= new Point(10, 10); Dimension dimension = new Dimension(2, 2); CustomCanvas(Dimension dimension){ this.dimension = dimension; this.init(); addListeners(); } private void init(){ oldLocation= new Point(0, 0); location= new Point(0, 0); } public void paintLine(){ if ((location.x!=oldLocation.x) || (location.y!=oldLocation.y)) { repaint(location.x,location.y,1,1); } } private void addListeners(){ addMouseListener(new MouseAdapter(){ @Override public void mousePressed(MouseEvent me){ oldLocation = location; location = new Point(me.getX(), me.getY()); paintLine(); } @Override public void mouseReleased(MouseEvent me){ oldLocation = location; location = new Point(me.getX(), me.getY()); paintLine(); } }); addMouseMotionListener(new MouseMotionAdapter() { @Override public void mouseDragged(MouseEvent me){ oldLocation = location; location = new Point(me.getX(), me.getY()); paintLine(); } }); } @Override public void paint(Graphics g){ super.paint(g); g.setColor(Color.red); g.drawLine(location.x, location.y, oldLocation.x, oldLocation.y); } @Override public Dimension getMinimumSize() { return dimension; } @Override public Dimension getPreferredSize() { return dimension; } } class CustomFrame extends JPanel { JPanel displayPanel = new JPanel(new BorderLayout()); CustomCanvas canvas = new CustomCanvas(new Dimension(200, 200)); public CustomFrame(String titlu) { canvas.setBackground(Color.white); displayPanel.add(canvas, BorderLayout.CENTER); this.add(displayPanel); } } public class CustomCanvasFrame { public static void main(String args[]) { CustomFrame panel = new CustomFrame("Test Paint"); JFrame f = new JFrame(); f.add(panel); f.pack(); SwingConsole.run(f, 700, 700); } } ```