重绘方法不起作用

Question

I'm trying creating an AVL tree by inserting its elements from text field, and then draw the tree by pressing on button "draw". My problem is that when I store random elements in the tree in the main and run the program the paint method works fine and the tree painted on the frame, but when I use text field to insert the elements and call repaint method in the actionPerformed method for draw button it does not paint anything. Can someone help me to know what is wrong in the actionPerformed method for draw button and why repaint method does not respond.

This is my first panel which contains all components

public class PanelComponents extends JPanel {

private JButton insertB;
private JButton drawB;

private JTextField insertTF;
private AvlTree<Integer> avl = new AvlTree<Integer>();// use AVL tree class
private TreeCanvas treeCanvas;

public PanelComponents() {

    setPreferredSize(new Dimension(780, 500));

    insertB = new JButton("insert");
    drawB = new JButton("draw");
    insertTF = new JTextField(7);
    createTreeCanvas();

    insertB.addActionListener(new ActionListener() {

        // here is the event handler
        public void actionPerformed(ActionEvent e) {
                int number = Integer.parseInt(insertTF.getText());
                avl.insert(number);
        }
    });

    drawB.addActionListener(new ActionListener() {

        // here is the event handler
        public void actionPerformed(ActionEvent e) {
            if (avl.isEmpty()) return;
            treeCanvas.setRoot(avl.getRoot());
            treeCanvas.repaint();


        }
    });
    add(insertTF);
    add(insertB);
    add(drawB);
}

private TreeCanvas createTreeCanvas() {
    if (treeCanvas == null) {
        treeCanvas = new TreeCanvas();
        treeCanvas.setBounds(5,5,680,230);
        add(treeCanvas);
    }
    return treeCanvas;
}

}

This is the demo class

public class TreeDemo {
public TreeDemo(){
    /**
     * when I use this way of inserting the tree painted 
     */
    //      AvlTree<Integer> t = new AvlTree<Integer>();
   //       t.insert (new Integer(2));
   //       t.insert (new Integer(1));
   //       t.insert (new Integer(4));
   //       t.insert (new Integer(5));
   //       t.insert (new Integer(9));
   //       t.insert (new Integer(3));
   //       t.insert (new Integer(6));
   //       t.insert (new Integer(7));
   //       TreeCanvas b =new TreeCanvas();
   //       b.setRoot(t.getRoot());

            JFrame frame = new JFrame("AVL Tree");
            PanelComponents panel = new PanelComponents();
   //       frame.add(b);  
            frame.add(panel);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
            frame.setSize(1000, 700);

}

  public static void main (String[] args){

      new TreeDemo();
}}

This class is used to paint the tree on panel and it works fine. You do not need to go through it

public class TreeCanvas extends JPanel {

private static final int NODE_WIDTH = 30;
private static final int ROW_GAP = 10;
private AvlNode<Integer> root;

public TreeCanvas() {
    root = null;
}

interface RenderNode {
    public void draw(Graphics g, AvlNode<Integer> parent, Point parentLoc,
            AvlNode<Integer> child, Point childLoc);
}

public void paint(Graphics g) {
    super.paint(g);
    int startX = getWidth() / 2;
    int startY = ROW_GAP + (NODE_WIDTH / 2);
    render(g, null, null, root, new Point(startX, startY), getWidth() / 2,
        new RenderNode() {public void draw(Graphics g, AvlNode<Integer> 
                    parent, Point parentLoc, AvlNode<Integer> child, Point childLoc) {
        if (parent != null) {
        g.setColor(Color.black);
        g.drawLine(parentLoc.x, parentLoc.y, childLoc.x,childLoc.y);
                    }
                }
            });
    render(g, null, null, root, new Point(startX, startY), getWidth() / 2,
        new RenderNode() {
       public void draw(Graphics g, AvlNode<Integer>parent,
                    point parentLoc, AvlNode<Integer> child, Point childLoc) {
                    child.draw(g, childLoc);
                }
            });
}

private void render(Graphics g, AvlNode<Integer> parent, Point parentLoc,
        AvlNode<Integer> child, Point childLoc, int spacing, RenderNode    
         callback) {

    if (child == null)
        return;

    callback.draw(g, parent, parentLoc, child, childLoc);
    int nextY = childLoc.y + (ROW_GAP + NODE_WIDTH);

    render(g, child, childLoc, child.getLeft(), new Point(childLoc.x
            - (spacing / 2), nextY), spacing / 2, callback);
    render(g, child, childLoc, child.getRight(), new Point(childLoc.x
            + (spacing / 2), nextY), spacing / 2, callback);
}

        public void setRoot(AvlNode<Integer> root){
    this.root = root;
}
}

Answer 1

All JPanels require to be revalidated before being repainted, or else nothing would change.

Revalidating marks the panel as changed so it would be considered for repainting.

So here would be the code which does that:

treeCanvas.revalidate(); //revalidate first. 

treeCanvas.repaint(); //then repaint.

(they have to be revalidated because they are marked as valid right after being first painted, and revalidating it marks it as invalid so it can be repainted)

Answer 2

My problem is that when I store random elements in the tree in the main and run the program the paint method works fine and the tree painted on the frame

I don't know how the code works. All you do is:

TreeCanvas b =new TreeCanvas();
b.setRoot(t.getRoot());

So that creates a panel, but I don't see where you add the panel to the frame anywhere.

Anyway, I would say your problem is with layout managers. All the classes you create extend JPanel which by default use a FlowLayout . In some of the code you then just add components to the panel so the layout manager will then determine the size/location of the components based on the "preferred size" of the components.

The problem is that your TreePanel class has a preferred size of 0, to there is nothing to paint. You need to override the getPreferredSize() method of the class to return the size of the panel so the layout managers can work properly. Do not attempt to be using setBounds() in your code. The layout manager will ignore that code.

Once you fix the layout issue then all the other suggestions are still valid:

1. override paintComponent() not paint()
2. invoke revalidate() and repaint() after updating the tree