2

The two examples shown below are same. Both are supposed to produce same result e.g. generate the coordinates of images displayed on JPanel. Example 1, works perfectly (print the coordinates of images), however example 2 returning 0 for the coordinate.

I was wondering why because, I have put the setvisible (true) after adding the panel, in both examples. The only difference is that example 1 used extends JPanel and example 2 extends JFrame

EXAMPLE 1:

    public class Grid extends JPanel{
       public static void main(String[] args){
          JFrame jf=new JFrame();
          jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);      
          final Grid grid = new Grid();
          jf.add(grid);
          jf.pack();

          Component[] components = grid.getComponents();        
          for (Component component : components) {
           System.out.println("Coordinate: "+ component.getBounds());       
          }   

          jf.setVisible(true);        
        }
    }

EXAMPLE 2:

public class Grid extends JFrame {

  public Grid () {
    setLayout(new GridBagLayout());
    GridBagLayout m = new GridBagLayout();
    Container c = getContentPane();
    c.setLayout (m);
    GridBagConstraints con = new GridBagConstraints();

    //construct the JPanel
    pDraw = new JPanel();
    ...
    m.setConstraints(pDraw, con);
    pDraw.add (new GetCoordinate ()); // call new class to generate the coordinate
    c.add(pDraw);

    pack();
    setVisible(true);
    }

    public static void main(String[] args) {
       new Grid();
    }
   }
4

3 回答 3

2

The problem is that in the second example, you are trying to print out the bounds of a component before the component has been added to its container (by calling add()) and before the frame's contents have been laid out (by calling pack()).

Here is my attempt to reproduce Example 1. ...

Here is my attempt to reproduce Example 2. I added the SwingUtilities call to put things in the right thread, and I filled in the contents of the GetCoordiates constructor with help from your comments:

class GetCoordinate extends JLabel {
    public GetCoordinate() {
        setText("Foo!");
        System.out.println("Coordinate: " + this.getBounds());
    }
}

public class Grid extends JFrame {
    public Grid() {
        setLayout(new GridBagLayout());
        GridBagLayout m = new GridBagLayout();
        Container c = getContentPane();
        c.setLayout(m);
        GridBagConstraints con = new GridBagConstraints();

        // construct the JPanel
        final JPanel pDraw = new JPanel();
        m.setConstraints(pDraw, con);
        pDraw.add(new GetCoordinate()); // call new class to generate the
                                        // coordinate
        c.add(pDraw);

        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Grid();
            }
        });
    }
}

Just as you described, it prints out a size of zero:

Coordinate: java.awt.Rectangle[x=0,y=0,width=0,height=0]

However, if you print out the size after the component has been added and the frame has been packed, it should work. Here is a modified version of my Example 2, where I added a method GetCoordinate.printBounds() and call that method everything has been added and laid out:

class GetCoordinate extends JLabel {
    public GetCoordinate() {
        setText("Foo!");
        // Let's not try to do this here anymore...
//        System.out.println("Coordinate: " + this.getBounds());
    }

    public void printBounds() // <-- Added this method
    {
        System.out.println("Coordinate: " + this.getBounds());
    }
}

public class Grid extends JFrame {
    public Grid() {
        setLayout(new GridBagLayout());
        GridBagLayout m = new GridBagLayout();
        Container c = getContentPane();
        c.setLayout(m);
        GridBagConstraints con = new GridBagConstraints();

        // construct the JPanel
        final JPanel pDraw = new JPanel();
        m.setConstraints(pDraw, con);
        final GetCoordinate content = new GetCoordinate();
        pDraw.add(content);
        c.add(pDraw);

        pack();
        setVisible(true);
        content.printBounds();  // <-- Added this
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Grid();
            }
        });
    }
}

With these changes, I get the following console output, including a nonzero size for my content:

Coordinate: java.awt.Rectangle[x=5,y=5,width=23,height=16]

于 2010-03-09T02:14:24.910 回答
0

此类异常的一个常见原因是未能在EDT上启动。在这种情况下，我无法从您的代码中看出有什么不同：特别是，不清楚第二个示例的打印位置。

于 2010-03-09T02:07:12.453 回答
0

康托

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author LENOVO G40
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new FrmMenuUTama().setVisible(true);
    }
}
于 2017-07-14T16:31:31.037 回答